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Introduction In the computer field, a buffer refers to a buffer register, which is divided into two types: input buffer and output buffer. The function of the former is to temporarily store the data sent by the peripheral so that the processor can take it away; the latter is to temporarily store the data sent by the processor to the peripheral. With the numerical control buffer, the high-speed CPU and the slow-speed peripherals can coordinate and buffer to realize the synchronization of data transmission. Since the buffer is connected to the data bus, it must have a three-state output function. Catalog Introduction Ⅰ Three-State Buffer Meaning Ⅱ Buffers in the Java Language 2.1 Buffer 2.2 Data Transmission 2.3 Mark and Reset 2.4 Invariants 2.5 Clear Reverse Rewind 2.6 Read-Only Buffer 2.7 Thread Safety 2.8 Call Chain Ⅲ EDA Code Ⅳ Verilog HDL Model and Simulation of Tri-state Buffer 4.1 Tri-state Buffer IC 4.2 Application Example of 74LS541 as Input Port 4.3 Multiplexer (MUX) Ⅴ FAQ Ⅰ Three-State Buffer Meaning Three-state buffer (tri-state buffer), also known as three-state driver, its three-state output is controlled by the enable output terminal. When the enable output is valid, the device realizes normal logic state output (logic 0, logic 1); when the enable input is invalid, the output is in a high-impedance state, which is equivalent to disconnecting from the connected circuit. Figure 1. Tristate Buffers A buffer is one of the digital components, it does not perform any operation on the input value, and its output value is the same as the input value. It plays an important role in the design of the computer. There are two types of buffers. In addition to tri-state buffers, there are also conventional buffers (regular buffers).Conventional buffers always output the value directly, which is used to output current to higher-level circuitry. The tri-state buffer has an optional card input, denoted by E, in addition to the functions of a conventional buffer. E=0 and E=1 have different output values. Figure 2. Tristate Buffer Symbols When E=1, it is gated, and its input is directly sent to the output.If E=0, the buffer is blocked. No matter what value is input, the output is always high impedance. The high-impedance state can drop the current low enough that the buffer-like output is not connected to anything.In the design of the CPU, the DC load capacity of the general output line can drive a TTL load, and in the connection, an address line or data line of the CPU may be connected to multiple memory chips, but the memory chips are all MOS circuits. It is a capacitive load, and the DC load is much smaller than the TTL load. Therefore, in a small system, the CPU can be directly connected to the memory, but a buffer needs to be added in a large system.In order to reduce the number of information transmission lines, the information transmission lines in most computers are in the form of buses, that is, all the same type of information to be transmitted goes through the same group of transmission lines, and the information is transmitted in time-sharing. There are generally three groups of buses in the computer, namely the data bus, the address bus and the control bus. In order to prevent information from interfering with each other, it is required that any register or memory hung on the bus, etc., its transmission end can not only show two information states of 0 and 1, but also should be able to show a third state-high impedance state. That is, it seems that their outputs are disconnected at this time, which has no effect on the bus state, and the bus can be occupied by other devices at this time. The above functions can be realized. In addition to the input and output terminals, it also has a control terminal, please see the figure below. Figure 3. Three-state Output Buffer Register When E=1, the output=input, the bus is driven by the device at this time, and the data on the bus is determined by the input data.When E=0, the output terminal is in a high-impedance state, and the device has no effect on the bus. When the output terminal of the register is connected to the three-state gate, and then the output terminal of the three-state gate is connected with the bus, the stage-rush register of the three-state output is formed. Since the one-way tri-state gate is used here, the data can only be output from the register to the data bus. If you want to achieve bidirectional transmission, you will use a bidirectional tri-state gate. Figure 4. Three-state Gate Ⅱ Buffers in the Java Language 2.1 Buffer Directly known subclasses of java.nio.Buffer: ByteBuffer, CharBuffer, DoubleBuffer, FloatBuffer, IntBuffer, LongBuffer, ShortBuffer public abstract classBufferextendsObject. A container for data of a specific basic type.A buffer is a linear finite sequence of elements of a particular primitive type. In addition to content, the basic properties of a buffer include capacity, limitation, and location.1) The capacity of a buffer is the number of elements it contains. The capacity of the buffer cannot be negative and cannot be changed.2) The limit of the buffer is the index of the first element that should not be read or written. A buffer's limit cannot be negative and cannot be larger than its capacity.3) The position of the buffer is the index of the next element to be read or written. The buffer's position cannot be negative and cannot be larger than its limit. This class has a subclass for each non-boolean primitive type. 2.2 Data Transmission Each subclass of this class defines two get and put operations:A relative operation reads or writes one or more elements, starting at the current position and incrementing the position by the number of elements transferred. If the requested transfer exceeds the limit, a relative get operation will throw a BufferUnderflowException, and a relative put operation will throw a BufferOverflowException. In both cases, no data is transferred.Absolute operations take explicit element indices, which do not affect position. Absolute get and put operations will throw IndexOutOfBoundsException if the index parameter exceeds the limit. Of course, I/O operations through the appropriate channel (usually related to the current position) can also transfer data to and from the buffer. 2.3 Mark and Reset The mark is an index to which the buffer's position is reset when the reset method is called. It is not always necessary to define a marker, but when defining a marker, you cannot define it as a negative number, and you cannot make it larger than the position. If a marker is defined, it will be discarded when the position or limit is adjusted to a value less than the marker. Calling the reset method will cause an InvalidMarkException to be thrown if the mark is not defined. 2.4 Invariants Mark, position, limit, and capacity values obey the following invariants:0<=mark<=position<=limit<=capacity, newly created buffers always have a 0 position and an undefined mark. The initial limit can be 0 or some other value, depending on the buffer type and how it is built. In general, the initial contents of the buffer are undefined. 2.5 Clear Reverse Rewind In addition to methods for accessing position, limitation, capacity values, and methods for marking and resetting, this class defines the following operations that can be performed on buffers.clear() prepares the buffer for a series of new channel reads or relative put operations. It sets the limit to the capacity size and the position to 0.flip() prepares the buffer for a series of new channel write or relative get operations. It sets the limit to the current position, then the position to 0.rewind() prepares the buffer for rereading already contained data. It leaves the limit unchanged, setting the position to 0. 2.6 Read-Only Buffer Every buffer is readable, but not every buffer is writable. The mutate method of each buffer class is designated as an optional operation and will throw a ReadOnlyBufferException when called on a read-only buffer. A read-only buffer does not allow changes to its contents, but its tag, position, and limit values are mutable. Its isReadOnly method can be called to determine whether the buffer is read-only. 2.7 Thread Safety It is not safe for multiple current threads to use the buffer. If it is used by more than one thread, access to that buffer should be controlled through appropriate synchronization. 2.8 Call Chain Specifies that methods in this class return the buffer on which they were called (otherwise they would return no value). This operation allows method calls to be formed into a chain, like a sequence of statementsb.flip(); b.position(23); b.limit(42); can be replaced by the following short statement b.flip().position(23).limit(42);   Ⅲ EDA Code library ieee;use IEEE.STD_LOGIC_1164.all;ENTITY BUF3S ISPORT (INPUT:IN STD_LOGIC;ENABLE:IN STD_LOGIC;OUTPUT:OUT STD_LOGIC);END BUF3S;ARCHITECTURE BHV OF BUF3S ISBEGINPROCESS(ENABLE,INPUT)BEGINIF ENABLE='1'THEN OUTPUT<=INPUT;ELSE OUTPUT<='Z';END IF;END PROCESS;END BHV;   Ⅳ Verilog HDL Model and Simulation of Tri-state Buffer Figure 5. Verilog HDL Model and Simulation of Tristate Buffer 4.1 Tri-state Buffer IC Tristate buffers are often used for multiple data sources to share a (group) common line (bus). Figure 6. For Multiple Data Sources When all enable terminals of the decoder are valid, the combination of SS2~SS0 makes only one of /SELP~/SELW valid at the same time, so that one of the 8 data sources P~W drives SDATA. When the enable terminal is invalid, then none of the three-state gates are enabled, and the outputs are all high impedance.The MSI device 74LS541 contains 8 independent tri-state gates and shares two enable inputs. The logic diagram and logic symbols are as follows: Figure 7. 74LS541 Logic Diagram and Logic Symbol 4.2 Application Example of 74LS541 as Input Port Figure 8. Application Example of 74LS541 as Input Port The MSI device 74LS245 is an 8-bit tri-state bus transceiver with an enable output G and a direction selection input DIR to determine the transmission direction: when DIR=1, data is transmitted from A to B; when DIR=0, data is transmitted from B passed to A. The logic diagram and logic symbols are as follows: Figure 9. 74LS245 Logic Diagram and Logic Symbol   Figure 10. Bus   Figure 11. Verilog HDL Model of 8-bit Tri-state Bus Transceiver 4.3 Multiplexer (MUX) Multiplexers are also called data selectors, and are often abbreviated as MUX. It is a combinational logic circuit with multiple inputs and single outputs, denoted as n/1 or n-1.Logic function: Since the enable terminal EN is valid., when selecting the control variable, select one of the multiple input data to the output terminal. Figure 12. MUX Each value group of the n selection control variables corresponds to select one of the m=2n input data and then send it to the output terminal.Design of Commonly Used Multiplexers🔺8 to 1 Multiplexer Figure 13. 8 to 1 Multiplexer Function Description   Figure 14. 8 to 1 Logic Circuit Diagram Circuit package, Logic symbol Figure 15. Circuit Package   Figure 16. Logic Symbol 1 Out of 8 Verilog HDL Models Figure 17. 1 Out of 8 Verilog HDL Model   Figure 18. 8 Out of 1 Functional Simulation 🔺8 Out of 1 Multiplexer with Tri--state Output Figure 19. Function Description   Figure 20. 8 to 1 Logic Circuit Diagramof Three-state Output Circuit Package, Logical Symbol Figure 21. 74LS251 Circuit Package and Logical Symbol 1 Out of 8 Verilog HDL Model for Tri-state Output Figure 22. Verilog HDL Model Ⅴ FAQ 1. What is a buffer software?A reserved segment of memory within a program that is used to hold the data being processed. Buffers are set up in every program to hold data coming in and going out. In a video streaming application, the program uses buffers to store an advance supply of video data to compensate for momentary delays. 2. Is buffer safe to use?Buffer is a reliable, fast way to manage multiple social media accounts, from a user-friendly dashboard. 3. Why do we need buffering in OS?Computers have many different devices that operate at varying speeds, and a buffer is needed to act as a temporary placeholder for everything interacting. This is done to keep everything running efficiently and without issues between all the devices, programs, and processes running at that time. 4. Is a buffer hardware or software?A buffer is a data area shared by hardware devices or program processes that operate at different speeds or with different sets of priorities. The buffer allows each device or process to operate without being held up by the other. This term is used both in programming and in hardware. 5. What is tri-state buffer?A tri-state buffer is a logic inverter or a non-inverting buffer with a tri-state output stage. ... When the enable line is not activated the buffer output stage has a high output impedance (i.e., the Z state, as described above in section 10.15) and transmission of data is prevented. 6. What is the difference between buffer and tri-state buffer?A tri-state buffer is similar to a buffer, but it adds an additional "enable" input that controls whether the primary input is passed to its output or not. If the "enable" inputs signal is true, the tri-state buffer behaves like a normal buffer. 7. What is meant by tri-state buffer how it helps in reading and writing data from a register?Definition: A three-state bus buffer is an integrated circuit that connects multiple data sources to a single bus. The open drivers can be selected to be either a logical high, a logical low, or high impedance which allows other buffers to drive the bus. 8. What is tri-state TTL?Tri-state gates have additional circuitry via which the gate outputs can be enabled or disabled. This is very useful in digital systems where devices communicate via common wires called busses. Only one device can talk at a time; the others are disabled. 9. Which of the following is also known as tri-state?Explanation: The progression in the parallel ports provides a third register or an individual control bit which can make the pin in a high impedance state. An output port which can do this is also known as tri-state, that is, logic high, logic low and a high impedance state. 10. What is tri-state in microprocessor?Tristate means three states viz. Logic 0, Logic 1 and high impedance states. In high impedance state, the pin neither connected to supply nor to ground. Hence impedance at this pin is very high with respect to suppy as well as ground. Some pins of 8085 have three states. 11. How many buffer may active at any given time?At any one time, one buffer is actively being displayed by the monitor, while the other, background buffer is being drawn. 12. What is tri-state circuit?Tristate means a digital circuit output that can have 3 states: 0, 1 and High-Z or high impedance which is the circuit equivalent of “disconnected”. There are times when you want to have multiple digital circuits connected on a bus but not interfering with each other.

Ⅰ Introduction What exactly is a microprocessor? As our lives are becoming increasingly tech-centric and thus tech-dependent,  we have to examine this critical component closely. After all, microprocessors are built into computers, laptops, and smartphones, as well as smart home devices, gaming consoles, and self-driving cars. Microprocessors are what allow these devices to function. In this blog, we will discuss microprocessor basics and their applications across industries. Catalog Ⅰ Introduction Ⅱ What is a Microprocessor? Ⅲ Microprocessor Related Video: Ⅳ Features of Microprocessor Ⅴ Evolution of Microprocessors  Ⅵ Microprocessor Types Ⅶ Characteristics of CISC and RISC  Ⅷ Differences Between CISC and RISC Ⅸ Applications of Microprocessor 9.1 Practical Diagram Examples Ⅹ Microprocessor vs. Integrated Circuit--What’s the Difference? Ⅺ FAQ   Ⅱ What is a Microprocessor? A microprocessor is a Central Processing Unit (CPU) built on a single  Integrated Circuit  (IC) in a computer. A microcomputer is a digital computer with one microprocessor that serves as the CPU. It is a programmable, multipurpose, clock-driven, register-based electronic device that reads binary instructions from memory, accepts binary data as input, processes data according to those instructions, and outputs the results. The microprocessor is composed of millions of tiny components that work together, such as transistors, registers, and diodes. Figure1：Block Diagram of a Microcomputer  A microprocessor contains three parts: an  ALU , a control unit, and a register array. The  ALU performs arithmetic and logical operations on data from an input device or memory. The control unit manages the computer's instructions and data flow. Furthermore, a register array is composed of registers denoted by letters such as B, C, D, E, H, L, and accumulator.   Ⅲ Microprocessor Related Video: How to easily use HMC5883L Compass Sensor Microprocessor Video Description: In this video, we will understand the difference between microprocessor and microcontroller. Visually both microprocessor and microcontroller almost look identical but they are different in many aspects. They are different in terms of the application in which they are used, processing power, memory, cost and power consumption. So, in this video, you will understand the difference between microprocessor and microcontroller in all these aspects. Ⅳ Features of Microprocessor   Ⅴ Evolution of Microprocessors  We can classify microprocessors based on generation or size: First Generation (4 - bit Microprocessors  ) Intel Corporation introduced the first generation of microprocessors in 1971-1972. Because it was a 4-bit processor, it was dubbed the  Intel 4004 . It was a single-chip processor. It was capable of performing basic arithmetic and logical operations such as addition, subtraction, Boolean OR, and Boolean AND. I had a control unit that could fetch an instruction from storage memory, decode it, and then generate control pulses to execute it. Second Generation (8 - bit Microprocessor) Intel introduced the second generation of microprocessors in 1973. It was the first eight-bit microprocessor capable of performing arithmetic and logic operations on 8-bit words. It was known as the  Intel 8008 , and an improved version was known as the  Intel 8088 . Third Generation (16 - bit Microprocessor) The third generation microprocessors, introduced in 1978, were Intel's 8086, Zilog Z800, and 80286, which were 16-bit processors with minicomputer-like performance. Fourth Generation (32 - bit Microprocessors  ) The 32-bit microprocessor was introduced by several companies, but the most popular is the Intel 80386. Fifth Generation (64 - bit Microprocessors) From 1995 to the present, we have been in the fifth generation. Following 80856, Intel released a new processor, the  Pentium  processor, followed by the  Pentium Pro CPU.  which enables multiple CPU  s in a single system to achieve multiprocessing. Celeron, Dual, Quad, and Octa-Core processors are also improved, 64-bit processors.   Ⅵ Microprocessor Types Microprocessors are classified into three types: CISC (Complex Instruction Set Computer) The instructions are in a complex format, as the name implies. This means that a single instruction can contain several low-level instructions. Loading data from memory, storing data in memory, performing basic operations, and so on. Furthermore, a single instruction can have multiple addressing modes. Furthermore, because there are many operations in a single instruction, they use a small number of registers. Intel 386,  Intel 486 , Pentium, Pentium Pro, Pentium II, and other  CISC  processors are examples. RISC (Reduced Instruction Set Computer) As the name implies, the instructions in this are quite simple, and thus they execute quickly. Furthermore, the instructions are completed in a single clock cycle and only use a few addressing modes. Furthermore, it employs multiple registers, resulting in less interaction with memory. Examples include the IBM RS6000, DEC Alpha 21064, DEC Alpha 21164, and others. EPIC (Explicitly Parallel Instruction Computing) It enables parallel computation of instructions through the use of compilers. Furthermore, the complex instructions operate at lower clock frequencies. It also encodes the instructions in 128-bit bundles. Each bundle contains three instructions encoded in 41 bits each, as well as a five-bit template. This 5-bit template specifies the type of instructions and which instructions can be executed concurrently.   Ⅶ Characteristics of CISC and RISC  Characteristics of  CISC are as follows: Because the instructions are complex, so is the decoding of instructions.The size of instructions is larger than the size of a single word.It is possible for an instruction to take more than one clock cycle to execute.Because most operations are performed in memory, the number of registers is reduced.Address modes are also complicated.There are more data types. Characteristics of  RISC are as follows: Because the instruction is simple, so is the decoding of instructions.The size of the instructions is less than one word.It takes one clock cycle to execute an instruction.The number of registers has increased.The address modes are also straightforward.There are fewer data types.It has the potential to be used for pipelining.   Ⅷ Differences Between CISC and RISC RISCCISCIt focuses on the software.It focuses on the hardware.Uses the hardwired control unit.It uses a hardwired as well as a microprogrammed control unit.Uses transistors for more registers.Transistors are used for storing the complex instructions.The instructions have a fixed size.The size of instructions vary.It performs only register to register arithmetic operations.Besides the register to register operations, it can also perform register to memory or memory to register operations.Fewer registers are used.It requires more number of registers.As the instructions are individual the code is large.Multiple operations are present in single instruction hence, the code is small.Executes in one clock cycle.Takes more than one clock cycle for execution.Instructions have a size of one word.The size of instructions is greater than the one-word size.Examples are IBM RS6000, DEC Alpha 21064, DEC Alpha 21164, etc.Examples of CISC are Intel 386, Intel 486, Pentium, Pentium Pro, Pentium II, etc.     Ⅸ Applications of Microprocessor Household DevicesIndustrial Applications of MicroprocessorsTransportation IndustryComputers and ElectronicsIn MedicalsInstrumentationEntertainmentEmbedded Systems at HomeOffice Automation and PublicationCommunication   9.1 Practical Diagram Examples As stated by the term microprocessor typically refers to a microcomputer's central processing unit (CPU), which contains the arithmetic logic unit (ALU) and control units. Typically, it is implemented on a single LSI chip. This separates the operation's "brains" from the rest of the computer's units.   An example of microprocessor architecture The arithmetic logic unit (ALU) and the control unit for a microcomputer are housed in the microprocessor. It is linked to memory and I/O via buses, which transport data between the units. Figure2: microprocessor architecture     Microcomputer Example A microprocessor unit (MPU), a clock, and interfaces to memory and external input/output devices are typical components of a microcomputer. The units are linked by buses that transfer data between them. Figure3: Microcomputer   Buses: The exchange of information Information is transferred between microcomputer units via buses, which are groups of conductors. Each bit of information to be passed will have one conductor, e.g., 16 lines for a 16-bit address bus. Address, control, and data buses will be present.   Figure4: microcomputer units via buses     Ⅹ Microprocessor vs. Integrated Circuit--What’s the Difference? Integrated Circuit An integrated circuit is a semiconductor chip component that contains thousands to billions of transistors. It's difficult to imagine how this is possible, but it's not done by shrinking scores of typical 3-legged NPN transistors. An integrated circuit is instead constructed by assembling the basic structure of MOS transistors on a small piece of the silicon wafer. The MOS transistors are connected in such a way that they perform the same function as a larger setup.    Microprocessor An integrated circuit is a microprocessor, but not all integrated circuits are microprocessors. The microprocessor, like Professor X, is an intelligent piece of integrated circuits. It serves as the brain of circuits that require computing power. The first microprocessors had thousands of transistors on a silicon wafer, but the number has now reached billions. The  AMD  Epyc Rome chip, which was released in 2019, contains over 39 billion transistors. A microprocessor, unlike other integrated circuits, serves as a computing brain. It can execute logical and arithmetic instructions that have been programmed into it. A microprocessor is made up of three parts: an arithmetic and logic unit (ALU), a control unit.  and a register array.   Microprocessor vs. Integrated Circuit in Electronics Design Figure5: Mind the speed when working with a microprocessor. In electronics design, you're likely to work with integrated circuits. Working with a microprocessor can be a herculean task on occasion. It's a mistake to think that designing with a microprocessor is the same as designing with traditional integrated circuits. If you skip a couple of best practices in PCB design, you can still create a successful design if you're working with common ICs like differential transceivers or logic gates. In terms of power supply and speed, these passive ICs are typically quite robust. However, if you make the same mistakes in a design with a microprocessor, you will almost certainly encounter a slew of problems in the prototype. Microprocessors are notoriously power-hungry devices that typically operate at hundreds of Hertz or Gigahertz. It should go without saying that a microprocessor is extremely sensitive to the voltage applied to it. Ripples or a sudden drop in voltage can have a significant impact on the microprocessor's stability. Because the microprocessor communicates with memory via high-speed data buses, EMI is also a concern. High-speed data exchange can be a source of EMI, affecting nearby sensitive components. When designing with a microprocessor, you can't afford to make even the smallest mistake, so using the right PCB design and analysis software is essential. Cadence OrCAD supports high-speed signal simulation to identify problems early in the design process, as well as a plethora of other tools to help you get the job done right the first time.   Ⅺ FAQ 1. What is microprocessor in simple terms? A microprocessor is an electronic component that is used by a computer to do its work. It is a central processing unit on a single integrated circuit chip containing millions of very small components including transistors, resistors, and diodes that work together. 2. Are microprocessors used today? One or more microprocessors are used today in everything from the smallest embedded systems and handheld devices to the largest mainframes and supercomputers. 3. Are microprocessors in phones? Smartphones and other mobile devices have multiple microprocessors and microcontrollers. The main processor is a microprocessor with a bus to communicate with memory on separate chips (although often included in the same IC package) and buses to communicate with the rest of the equipment. 4. Do phones have RAM? Android phones have jumped from 4GB to 8GB RAM as standard, and we're now seeing phones with 12GB and 16GB of RAM — but Apple's iPhone has always gotten by with less. 5. How do microprocessors execute instructions? The instructions which are to be executed by microprocessor are first stored in the memory of the processor and then executed. But the processor does not execute the instructions directly. It reads the instruction byte by byte and then executes it. 6. What is microprocessor chips? Microprocessor chips (MPU) are silicon devices that serve as the central processing unit (CPU) in computers. They contain thousands of electronic components and use a collection of machine instructions to perform mathematical operations and move data from one memory location to another.

ⅠIntroductionThyristors are high-speed solid-state devices that can control motors, heaters, and lighting. Before we get into Thyristor Circuits. We'll look at the basic construction and operation of the Silicon Controlled Rectifier, also known as a Thyristor. Next, we'll look at how we can use thyristors and thyristor switching circuits to control much larger loads like lamps, motors, or heaters, among other things. CatalogⅠIntroductionⅡ Thyristors Circuits Related VideoⅢ What Is Silicon Controlled Rectifier?Ⅳ Construction of Silicon Controlled RectifierⅤ What is a Thyristor?Ⅵ Thyristor Switching Circuits6.1 Thyristor Circuit in DC6.2 AC Thyristor CircuitⅦ How an SCR Circuit Works with Thyristor Circuits?7.1 DC Thyristor / SCR Circuit7.2 Basic AC Thyristor / SCR Circuit7.3 AC SCR Circuit with Gate Phase ControlⅧ FAQ Ⅱ Thyristors Circuits Related VideoSilicon Control Rectifier SCR Basic AC Circuit Thyristors Circuits Video Description:  Silicon Control Rectifier SCR Basic AC Circuit Ⅲ What Is Silicon Controlled Rectifier?The Silicon Controlled Rectifier (SCR) is one of the most popular devices in the market. SCR can be found in a variety of applications such as rectification, power regulation, and inversion, among others. SCR, like a diode, is a unidirectional device that allows current in one direction but opposes it in the other gate. SCRs have the ability to turn ON or OFF, and their switching is controlled by biasing conditions and the gate input terminal.By varying the ON periods of the SCR, the average power delivered at the load can be varied. It is capable of handling tens of thousands of voltages and currents. Figure depicts the SCR symbol and its terminals.Figure1 :Silicon Controlled Rectifier   Ⅳ Construction of Silicon Controlled RectifierAs shown in the figure, an SCR has three terminals: anode, cathode, and gate. SCRs have the ability to turn ON or OFF, and their switching is controlled by biasing conditions and the gate input terminal.By varying the ON periods of the SCR, the average power delivered at the load can be varied. It is capable of handling tens of thousands of voltages and currents. Figure depicts the SCR symbol and its terminals.Figure2:Construction The SCR is manufactured using three different types of constructions: planar, Mesa, and press pack. Planar construction, in which all junctions in an SCR are diffused, is used for low-power SCRs. In a mesa type construction, junction J2 is formed by diffusion and the outer layers are alloyed to it as a result. This design is primarily used in high-power Silicon Controlled Rectifiers. The SCR is braced with plates made of molybdenum or tungsten to provide high mechanical strength. One of these plates is soldered to a copper stud, which is threaded to connect to the heat sink. Ⅴ What is a Thyristor?A thyristor is a four-layer solid-state semiconductor device made of P and N materials. When a gate receives a triggering current, it begins to conduct until the voltage across the thyristor device is biased forward. In this case, it functions as a bistable switch. To control a large amount of current flowing through the two leads, we must create a three-lead thyristor by combining the small amount of current with that current. This is referred to as control lead. If the potential difference between the two leads is less than the breakdown voltage, a two-lead thyristor is used to turn the device on.Figure3:Thyristor Ⅵ Thyristor Switching CircuitsDC Thyristor CircuitAC Thyristor circuit 6.1 Thyristor Circuit in DCWhen connected to a DC supply, we use a thyristor to control larger DC loads and current. The main advantage of using a thyristor in a DC circuit as a switch is that it provides a high current gain. Because a small gate current can control a large anode current, the thyristor is classified as a current-operated device.Figure4:Thyristor Circuit in DC 6.2 AC Thyristor CircuitWhen connected to an alternating current supply, the thyristor behaves differently because it is not the same as a DC-connected circuit. A thyristor is used as an AC circuit during one half of a cycle, causing it to turn off automatically due to its reverse biased condition. Figure6:AC Thyristor Circuit Ⅶ How an SCR Circuit Works with Thyristor Circuits?7.1 DC Thyristor / SCR CircuitMany applications call for an SCR circuit to control the operation of a DC load. This can be used for switching DC motors, lamps, or any other load.The basic SCR circuit shown below can control power to a load by using a small switch to initiate power application to the load.Figure7:Basic DC thyristor / SCR circuit With S1 closed and S2 open, no current will flow at first. The SCR circuit will turn on and the current will flow in the load only when S2 is closed and it triggers the gate by causing the gate current to flow.Until the anode circuit is broken, the current will continue to flow. S1 can be used for this. Another method is to place the switch S1 across the SCR and briefly close it, causing the voltage across the SCR to disappear and the SCR to stop conducting.Because of their functions in this SCR circuit, S1 and S2 may be referred to as the Off switch and the ON switch, respectively. In this configuration, S1 must be able to carry the full load current, while S2 must only carry the gate current. Once the SCR is turned on, the switch can be released and remain open because the SCR's action maintains the current flow through the device and thus the load.R1 connects the gate to the power supply via the switch. When S2 is closed, current flows through the resistor enters the gate and activates the SCR. The resistor R1 must be calculated to provide enough gate current to turn on the SCR circuit.R2 is included to reduce the SCR's sensitivity so that it does not fire on any noise that is detected. 7.2 Basic AC Thyristor / SCR CircuitWhen using a thyristor circuit with AC, a few changes must be made, as shown below.This is because alternating current reverses polarity throughout the cycle. This means that the SCR will become reverse-biased, effectively lowering the anode voltage to zero and causing it to turn OFF for one-half of each cycle. As a result, there is no need for an off switch because this is accomplished as part of the use of an alternating current supply.When using a thyristor circuit with AC, a few changes must be made, as shown below.This is because alternating current reverses polarity throughout the cycle. This means that the SCR will become reverse-biased, effectively lowering the anode voltage to zero and causing it to turn OFF for one-half of each cycle. As a result, there is no need for an off switch because this is accomplished as part of the use of an alternating current supply.Figure8: AC thyristor / SCR circuitThe circuit operates in a slightly different manner than the DC SCR circuit. When the switch is turned on, the circuit must wait for sufficient anode voltage to be available as the AC waveform progresses along its path. In addition, the SCR circuit will have to wait until the voltage within the gate section of the circuit is high enough to trigger the SCR. The switch must be in a closed position for this to work.Once triggered, the SCR will remain to conduct for the duration of the positive half of the cycle. As the voltage falls, the anode-cathode voltage will become insufficient to support conduction. At this point, the SCR will come to a halt.The SCR will then not operate during the negative half of the cycle. The process will only be repeated when the next positive half of the cycle returns. As a result, this circuit will only operate when the gate switch is closed.One disadvantage of using this type of SCR circuit is that it cannot supply more than 50% power to the load because it does not conduct during the negative half of the AC cycle because the SCR is reverse biased. 7.3 AC SCR Circuit with Gate Phase ControlBy varying the proportion of the half-cycle over which the SCR conducts, the amount of power reaching the load can be controlled. This can be accomplished by using an SCR circuit with phase control of the input gate signal.Figure9:AC thyristor circuit waveformsThe SCR gate signal is derived from an RC circuit consisting of R1, VR1, and C1 before the diode D1 when using the SCR circuit with phase control.Because the SCR is forward biased, only the positive half cycle of the waveform is of interest, as with the basic AC SCR circuit. During this half-cycle, the capacitor, C1, charges up from the AC supply voltage via the resistor network of R1 and VR1. The waveform at the positive end of C1 is seen to lag behind the input waveform, and the Gate is only triggered when the voltage at the capacitor's high end has risen sufficiently to trigger the SCR via D1. As a result, the SCR's turn-on time is delayed compared to what it would be if the RC network was not present. The VR1 value changes the delay and thus the proportion of the cycle over which the SCR operates. The power into the load can thus be adjusted in this manner. Figure10: AC thyristor circuit with gate phase control R1 is a series resistor that has been included to limit the minimum value for the resistor network to a value that will provide an acceptable gate current level for the SCR. The phase angle of the gate waveform must typically vary between 0° and 180° to provide complete control of the 50% of the cycle available for conduction with an SCR. These circuits demonstrate some of the fundamental concepts underlying the design of SCR thyristor circuits. They show how they work and how they can be used in their most basic form. One of the most important considerations when designing thyristor circuits is power dissipation. Because these circuits frequently handle high voltages and high power levels, power dissipation can be a significant factor in circuit design and operation. Ⅷ FAQ1. What does a thyristor do in a circuit?The primary function of a thyristor is to control electric power and current by acting as a switch. For such a small and lightweight component, it offers adequate protection to circuits with large voltages and currents (up to 6000 V, 4500 A).2. How thyristor acts as a switch?When connected to a direct current DC supply, the thyristor can be used as a DC switch to control larger DC currents and loads. When using the Thyristor as a switch it behaves like an electronic latch because once activated it remains in the “ON” state until manually reset3. What is difference between SCR and thyristor?Thyristor is a four semiconductor layer or three PN junction device. It is also known as “SCR” (Silicon Control Rectifier). The term “Thyristor” is derived from the words of thyratron (a gas fluid tube which works as SCR) and Transistor. Thyristors are also known as PN PN Devices.4. Is thyristor convert AC to DC?A single-phase thyristor rectifier converts an AC voltage to a DC voltage at the output. The power flow is bidirectional between the AC and the DC side.5. What are the advantages of thyristor?Advantages of Thyristor :It is easy to turn on. It is able to control AC power. It can switch high voltage, a high current device. It cost is very low. 

Introduction Operational amplifiers will oscillate in many practical applications. For example, there are many kinds of loads that will cause them to oscillate. A feedback network that is not properly designed can cause them to become unstable. Insufficient power supply bypass capacitors may also make them unstable. Even the input and output may oscillate into a single-port system. This article will tell some common causes that cause the op amp to oscillate and the corresponding countermeasures. Catalog Introduction Ⅰ Basic Op Amp Circuits Ⅱ Example: LTC6268 Amplifier Ⅲ Decompensated Amplifiers Ⅳ Feedback Network Ⅴ Load Problem Ⅵ Strange Impedance Ⅶ Power Ⅷ Conclusion Ⅸ FAQ Ⅰ Basic Op Amp Circuits Figure 1. shows a block diagram of a non-rail-to-rail amplifier. The input controls the gm box, which drives the gain node and is buffered at the output. The compensation capacitor Cc is the main frequency response component. The return pin of Cc should be grounded, if there is such a pin and the op amp is not grounded, the capacitor current will return to one or two power supplies. Figure 1. Block Diagram of a Non-Rail-to-Rail Amplifier Figure 2. is a block diagram of a rail-to-rail output amplifier. The output current of the input box gm is sent through a current coupler, which divides the current into two parts and supplies them to the output transistor. The frequency response is determined by two Cc/2s, which are actually connected in parallel. Figure 2. Block Diagram of a Rail-to-Rail Output Amplifier Figure 3. shows the frequency response of the ideal amplifier. Although the electrical principles of the two circuits are different, the behavior is similar. The single pole compensation formed by gm and Cc provides a unity gain bandwidth product frequency of GBF = gm/(2πCc). In the vicinity of GBF/Avol, the phase lag of these amplifiers changes from -180° to -270°, where Avol is the open-loop DC gain of the amplifier. When the frequency is much higher than this low frequency, the phase stays at –270°. This is the well-known "dominant pole compensation", where the Cc dominates the frequency response, hiding the various frequency limitations of the active circuit. Figure 3. Frequency Response of the Ideal Amplifier   Ⅱ Example: LTC6268 Amplifier Figure 4. shows the open-loop gain and phase response of the LTC6268 amplifier with frequency. The LTC6268 is a small and low-noise 500MHz amplifier with rail-to-rail output and only 3fA bias current. It can be used as a good example to illustrate the performance of real amplifiers. The -90° phase lag of the dominant pole compensation starts from about 0.1MHz, reaches -270° around 8MHz, and moves down by more than -270° when it exceeds 30MHz. In fact, all amplifiers have high frequency phase lag, except for the basic dominant compensation lag caused by the additional gain stage and output stage. Generally, the starting point of the additional phase lag is around GBF/10. Figure 4. Open-Loop Gain and Phase Response of the LTC6268 Amplifier with Frequency The stability of the feedback is a matter of loop gain and phase, or Avol multiplied by the feedback coefficient, which is the loop gain. If we connect the LTC6268 in a unity gain configuration, 100% of the output voltage is fed back. At very low frequencies, the output is the negative value of the "–" input, or the phase lags by -180°. Compensation adds a -90° hysteresis through the amplifier, introducing a –270° hysteresis from the "–" input to the output. When the loop phase lag increases to ±360° or its multiples, oscillation will occur, and the loop gain is at least 1V/V or 0dB. The phase margin is a measure of how much the phase lag differs from 360° when the gain is 1V/V or 0dB. Figure 4. shows that the phase margin is about 70° (10pF red curve) at 130MHz, and the phase margin as low as about 35° is feasible.A topic that is not often mentioned is gain margin, although it is an equally important parameter. When it is reduced to zero at some higher frequencies, the amplifier will oscillate if the gain is at least 1V/V or 0dB. As shown in Figure 4, when the phase drops to 0° (or a multiple of 360°, or –180° as shown in the figure), the gain is about –24dB around 1GHz. This is a very low gain and no oscillations will occur at this frequency. In fact, people want the gain margin to be at least 4dB.   Ⅲ Decompensated Amplifiers Although the LTC6268 is fairly stable at unity gain, there are still unstable op amps. By designing the amplifier compensation to be stable only at higher closed-loop gains, the design trade-off can provide a higher conversion rate, wider GBF, and lower input noise than the unity gain compensation scheme. Figure 5. shows the open loop gain and phase of the LTC6230-10. The amplifier is intended to be used with a feedback gain of 10 or greater, so the feedback network will attenuate the output by at least 10 times. Through this feedback network, you can find the frequency when the open-loop gain is 10V/V or 20dB, and find that the phase margin is 58° at 50MHz (±5V power supply). At unity gain, the phase margin is only about 0°, so the amplifier oscillates. Figure 5. LT6230-10 Gain and Phase Change with Frequency It is observed that when the closed-loop gain is higher than the minimum stable gain, all amplifiers will be more stable. Even a gain of 1.5 will make a unity gain stable amplifier much more stable.   Ⅳ Feedback Network The feedback network itself may also cause oscillations. In Figure 6, put a parasitic capacitor in parallel with the feedback divider resistor. It is inevitable that each terminal of each component on the circuit board has a capacitance of about 0.5pF to the ground, and there is also a wiring capacitance. Figure 6. Parasitic Capacitance In fact, the minimum capacitance of the node is 2pF, and there is about 2pF of wiring capacitance per inch of trace. The accumulated parasitic capacitance can easily reach 5pF. Using LTC6268, in order to reduce the power, we set the values of Rf and Rg to a very high 10kΩ. When Cpar = 4pF, the feedback network has a pole at 1/(2π*Rf||Rg*Cpar) or 8MHz. The phase lag of the feedback network is -atan(f/8MHz), we can estimate that the loop will have a phase lag of 360° around 35MHz. At this time, the phase lag of the amplifier is -261°, and the feedback network lags about -79°. At this phase and frequency, the amplifier still has a gain of 22dB, and the gain of the voltage divider is .At the 0° phase, the amplifier's 22dB multiplied by the feedback divider's –19dB produces a +3dB loop gain, and the circuit oscillates. In order to operate normally in the presence of parasitic capacitance, we must reduce the value of the feedback resistor so that the feedback pole can far exceed the unity gain frequency of the loop. That is, the ratio of the pole to the GBF should be at least 6 times.The input end of the op amp itself may also have a considerable capacitance, the same as Cpar. In particular, low noise and low Vos amplifiers have large input transistors and may have larger input capacitance than other types of amplifiers, and the input capacitance is loaded on the amplifier's feedback network. We need to consult the data sheet to understand how much capacitance will be connected in parallel with Cpar. Fortunately, the LT6268 has only 0.45pF capacitance, which is already very low for such a low noise amplifier. The macro model running on LTspice® provided free of charge by ADI can be used to simulate a circuit with parasitic capacitance. Figure 7. shows how to improve the capacitor tolerance of the voltage divider. Figure 7(a) shows a non-negative output amplifier configuration with Rin. Assuming that Vin is a low impedance source (<Rin), Rin will effectively attenuate the feedback signal without changing the closed-loop gain. And it will also reduce the impedance of the voltage divider and increase the feedback pole frequency, which is expected to far exceed GBF. In addition, Rin reduces the bandwidth around the loop and amplifies the input offset and noise.Figure 7(b) shows a negative output configuration. Rg still performs loop attenuation without changing the closed loop gain. In this case, the input impedance is not affected by Rg, but the noise, offset and bandwidth parameters will deteriorate.Figure 7(c) shows the preferred method of compensating Cpar in a non-inverting amplifier. If we set Cf* Rf = Cpar * Rg, then we have a "compensation attenuator", so that the feedback divider now has the same attenuation at all frequencies and solves the Cpar problem. The mismatch in the product will cause "bumps" in the passband of the amplifier and "shelf" in the response curve (At this time, the low-frequency response is flat, but becomes straight near f = 1/2 * Cpar * Rg.).Figure 7(d) shows the equivalent Cpar compensation for the negative output amplifier. The frequency response must be analyzed to find a correct Cf, and the bandwidth of the amplifier is part of the analysis.Here are some comments on current feedback amplifiers (CFA) in turn. If the amplifier in Figure 7(a) is a CFA, then "Rin" has little effect on changing the frequency response, because the negative input is very low impedance and actively copies the positive input. The noise index will degrade slightly, and the additional negative input bias current will actually appear in the form of Vos/Rin. Similarly, in terms of frequency response, the circuit in Figure (b) is not changed by "Rg". The inverting input is not just a virtual ground, it is a real ground with low impedance, and Cpar has been tolerated (only in negative output mode). The DC error is similar to the situation shown in (a), (c) and (d) may be the preferred solution for voltage input op amps, but CFA can't tolerate a direct feedback capacitor without oscillation at all.   Ⅴ Load Problem Just as the feedback capacitor can damage the phase margin, the load capacitor can do the same. Figure 8 shows the change in LTC6268 output impedance with frequency in the case of several gain settings. Note that the unity gain output impedance is lower than the output impedance at higher gains. Full feedback enables the open-loop gain to reduce the inherent output impedance of the amplifier. Therefore, in Figure 8, the output impedance at a gain of 10 is generally 10 times the output impedance at unity gain. Since the feedback attenuator reduces the loop gain, the gain around the loop is 1/10, otherwise it will reduce the closed-loop output impedance. The open-loop output impedance is about 30, which is obvious in the high-frequency flat region of the curve with a gain of 100. In this area, from around gain bandwidth frequency (about 100) to gain bandwidth frequency, there is not enough loop gain to reduce the open loop output impedance. Figure 8. Impedance and Frequency of LTC6268 Under Three Gain Conditions The capacitor load will cause the phase lag and amplitude attenuation of the open-loop output impedance. For example, a 50pF load and our LTC6268 output impedance form another pole at 106MHz, where the output has a –45° phase lag and –3dB attenuation. At this frequency, the amplifier has a phase of -295° and a gain of 10dB. Assuming unity gain feedback is used, we have not fully realized the oscillation because the phase is not brought to ±360° (at 106MHz). However, at 150MHz, the amplifier has 305° phase lag and 5dB gain. The phase of the output pole is –atan(150MHz/106MHz) = -55°, and the gain is .Multiplying the gain cyclically, we get a 360° phase and +0.2dB gain, which is another oscillator. 50pF seems to be the minimum load capacitance that will force the LTC6268 to oscillate.The most common way to prevent oscillations caused by the load capacitor is to simply connect a small resistor in series to the capacitor after the feedback connection. The resistance value of 10Ω to 50Ω will limit the phase lag that may be caused by the capacitive load and isolate the amplifier and low capacitive impedance when the speed is very high. Disadvantages include DC and low frequency errors that vary with load resistance characteristics, capacitive load frequency response is limited, and signal distortion caused if the load capacitance is not constant when the voltage changes.Increasing the closed-loop gain of the amplifier can often prevent the oscillation caused by the load capacitance. Operating the amplifier with a higher closed-loop gain means that at frequencies where the loop phase is ±360°, the feedback attenuator also attenuates the loop gain. For example, if we use the LTC6268, its closed-loop gain is +10, then we will see that the amplifier has a gain of 10V/V or 20dB at 40MHz and a phase lag of 285°. To ignite the oscillation, an output pole is required, causing an additional 75° hysteresis. By -75° =-atan(40MHz/Fpole) →Fpole =10.6MHz, we can find the output pole. This pole frequency comes from a load capacitance of 500pF and an output impedance of 30Ω. The output pole gain is .When the unloaded open-loop gain is 10, the loop gain at the oscillation frequency point is 0.26, so there is no oscillation this time, at least no oscillation caused by the simple output pole. In this way, we increased the tolerable load capacitance from 50pF to 500pF by increasing the closed-loop gain.In addition, unterminated transmission lines are also very bad loads because they will cause "runaway" impedance and phase changes that repeat with frequency (See the impedance of an unterminated 9-foot cable in Figure 9).If your amplifier can safely drive the cable under certain low-frequency resonance conditions, it is likely to oscillate at a higher frequency because its own phase margin is reduced. If the cable must be unterminated, a "back-match" resistor in series with the output can isolate the cable's extreme impedance changes. In addition, even if the transient reflection from the this end of the cable just recoils back to the amplifier, if the resistance of the backward matching resistor matches the characteristic impedance of the cable, the resistor can properly absorb this energy. If the backward resistor does not match the cable impedance, some energy will be reflected from the amplifier and terminals, and back to the unterminated end. When the energy reaches this end, it is quickly reflected back to the amplifier. As a result, there is a series of pulses bouncing back and forth, but attenuate each time. Figure 9. Impedance and Phase of the Unterminated Coaxial Cable Figure 9 shows a more complete output impedance model. The ROUT is the same as what we discussed in the LTC6268, and it is also 30Ω, in addition, add the Lout item. This is a combination of physical inductance and electronic equivalent inductance. The physical package, bonding wire, and external inductance add up to 5nH to 15nH. The smaller the package, the smaller the total value. Figure 10. Inductive Component of Amplifier Output Impedance In addition, any amplifier has an electrical inductance of 20nH to 70nH, especially bipolar devices. The finite Ft of the device turns the parasitic base resistance of the output transistor into an inductance. The harm is that Lout and CL may interact to form a series resonant circuit, then the same problem comes again. If there is no greater phase lag in the loop, the impedance of the series resonant circuit may drop to a level that Rout cannot drive. This may cause oscillations. For example, set Lout = 60nH and CL = 50pF. Resonant frequency is .Just within the passband of the LTC6268. In fact, this series resonant circuit is loaded to the output terminal during resonance, which changes the phase of the loop greatly near the resonant frequency. Unfortunately, Lout is not mentioned in the amplifier's data sheet, but its effect can sometimes be seen on the open-loop output impedance circuit. In short, for amplifiers with a bandwidth of less than 50MHz, this effect is not important.One solution is shown in Figure 10. Rsnub and Csnub form a so-called "shock absorber" whose purpose is to reduce the Q value of the resonant circuit so that the resonant circuit does not have a very low resonant impedance to the output of the amplifier. The value of Rsnub is usually estimated as the reactance of CL to reduce the Q value of the output resonance circuit to about 1. Adjust the size of Csnub to fully insert Rsnub into the output resonance frequency, that is, the reactance of Csnub <Cl. Csnub = 10 * CL is practical. Csnub unloads the amplifier at intermediate and low frequencies, especially at DC. If it is very large, Rsnub will put a heavy load on the amplifier at intermediate frequency, which will affect the low frequency, gain accuracy, closed-loop bandwidth and distortion. However, after a little fine-tuning, shock absorbers are often useful for controlling reactive loads, but shock absorbers must be adjusted through experiments. Figure 11: Using an Output Shock Absorber The negative input of the current feedback amplifier is actually a buffer output and will also have the series characteristics shown in Figure 8. Therefore, it may oscillate under the action of Cpar, just like the output terminal. You should try to reduce Cpar and any related inductance. Unfortunately, the damper on the negative input terminal modifies the relationship between closed-loop gain and frequency, so it is not very useful.   Ⅵ Strange Impedance Many amplifiers have an abnormal input impedance at high frequencies. This is most true for amplifiers with two input transistors in series, such as the Darlington configuration. Many amplifiers have PNP/NPN transistor pairs at the input, and their behavior changes with frequency similar to the Darlington configuration. The real part of the input impedance will become negative at some frequencies (generally much higher than GBF). Inductive source impedance will resonate with the input and circuit board capacitance, and negative real components may provoke oscillations. When driving with unterminated cables, this can also cause oscillations at many repetition frequencies. If it is inevitable to use a long inductive wire at the input, you can disconnect the wire with several series-connected resistors that can absorb energy, or install a medium-impedance shock absorber (about 300Ω) on the input lead of the amplifier.   Ⅶ Power The last source of oscillation to consider is power supply bypass. Figure 10 shows part of the output circuit. LVS+ and LVS– are the unavoidable packaging, IC bond wires, the physical length of the bypass capacitor (inductive like any conductor), and the series inductance of the circuit board traces. It also includes the external inductance that connects the local bypass component to the rest of the power bus (if not the power plane). Although 3nH to 10nH may seem small, at 200MHz, it is 3.8 to 12Ω. If the output transistor conducts a large high-frequency output current, there will be a voltage drop across the power inductor. Figure 12. Power Supply Bypass Capacitor Details The rest of the amplifier needs a noise-free power supply, because these parts cannot suppress power supply noise as the frequency changes. In Figure 13 we can see the power supply rejection ratio (PSRR) of the LTC6268 with frequency. In all operational amplifiers, because there is no ground pin, the compensation capacitor is connected to the power supply, which will couple power supply noise into the amplifier, and gm must cancel this noise. Due to the compensation, PSRR decreases with 1/f, in addition, the power supply rejection actually increases after 130MHz. Figure 13. LTC6268 Power Supply Rejection with Frequency Variation At 200MHz, due to the increase of PSRR, the output current may interfere with the power supply voltage inside the LVs inductor. Through the amplification of PSRR, the interference becomes a strong amplifier signal, driving the output current, generating internal power signals, etc., causing the amplifier to oscillate. This is why the power supplies of all amplifiers must be carefully bypassed with traces and components with very small inductance. In addition, the power supply bypass capacitor must be much larger than any load capacitor.If consider the frequency around 500MHz, then the range 3nH to 10nH becomes 9.4Ω to 31.4Ω. This is enough for the output transistor to generate self-oscillation by its inductance and IC component capacitance, especially when the output current is large (transistor gm and bandwidth increase). Because the bandwidth of transistors is very large, special attention needs to be paid, especially at high output currents.   Ⅷ Conclusion In short, the designer needs to consider the parasitic capacitance and inductance associated with each op amp terminal and the natural characteristics of the load. Usually the designed amplifier is very stable in the nominal environment, but each application needs to analyze it by itself.   Ⅸ FAQ 1. Does your op amp oscillate?Well, it shouldn't. We analog designers take great pains to make our amplifiers stable when we design them, but there are many situations that cause them to oscillate in the real world. ... Improperly designed feedback networks can cause instability. Insufficient supply bypassing can offend. 2. What is oscillator in op amp?An oscillator is an electronic circuit that produces a periodic signal. ... The feedback network takes a part of the output of amplifier as an input to it and produces a voltage signal. This voltage signal is applied as an input to the amplifier. 3. What causes an amplifier to oscillate?Causes of parasitic oscillationParasitic oscillation in an amplifier stage occurs when part of the output energy is coupled into the input, with the correct phase and amplitude to provide positive feedback at some frequency. ... Similarly, impedance in the power supply can couple input to output and cause oscillation. 4. How do you compensate an op amp?Another effective compensation technique is the miller compensation technique and it is an in-loop compensation technique where a simple capacitor is used with or without load isolation resistor (Nulling resistor). That means a capacitor is connected in the feedback loop to compensate the op-amp frequency response. 5. How can an op amp improve stability?To ensure stability, the value of RX should be such that the added zero (fZ) is at least a decade below the closed loop bandwidth of the op amp circuit. With the addition of RX,circuit performance will not suffer the increased output noise of the first method, but the output impedance as seen by the load will increase. 6. What are the requirements of oscillations in an amplifier?Oscillations around the 3dB bandwidth of the amplifier are usually due to input/output feedback. Higher frequency oscillations may only be visible on a spectrum analyzer. They may cause waveform distortion and be affected by touching the amplifier on power and signal cables. 7. How do you stop an oscillating op amp?If the op-amp still oscillates, try these things, in this order:1) Add a small resistor to the op-amp's output, either inside or outside the feedback loop. ...2) Do the same as in the previous step, except use a ferrite bead or chip ferrite instead of the resistor. ...3) Raise the amp's gain a bit. 8. How do you increase the gain margin of an op amp?You can increase the phase margin by making a dominant pole nearer to the zero frequency origin. This is accomplished by compensating the op amp through adding a shunting capacitor in the highest impedance node of the amplifier. This is a very well known technique which is used commonly to increase the phase margin. 9. Why the gain of op amp deteriorate with frequency?All opamps have a limit on upper frequency. In a LPF, at low frequencies, the output amplitude is equal to input. But as the frequency increases, the capacitive reactance decreases and the output amplitude starts to decrease. 10. What is used to avoid or minimize instability in amplifiers?It is often desirable to use capacitance to ground from an amplifier's active input terminals to reduce high-frequency interference, RFI and EMI. This filter capacitor has a similar effect on op amp dynamics as increased stray capacitance. 11. Why op amps oscillate an intuitive look at two frequent causes?With delay in the loop, the amplifier does not immediately detect its progress toward the final value. ... It overreacts by racing too quickly toward the proper output voltage. Note the faster initial ramp rate with delayed feedback. 12. How does an op-amp oscillator work?The Op-amp Multivibrator is an astable oscillator circuit that generates a rectangular output waveform using an RC timing network connected to the inverting input of the operational amplifier and a voltage divider network connected to the other non-inverting input.

Introduction Potentiometer is a common instrument that uses compensation principle and comparison method to accurately measure DC potential difference or power supply electromotive force. It has high accuracy, convenient use, and stable and reliable measurement results. But even so, when we do potentiometer experiments, we still have to deal with different error problems. The content of this article tells you how to avoid too many errors without getting too large deviations in the experimental results. Potentiometer Experiment (Compare EMF of Two Cells) Catalog Introduction Ⅰ Potentiometer Principle Analyses 1.1 Compensation Principle 1.2 Operational Principle Ⅱ UJ25 DC Potentiometer Overview Ⅲ UJ25 DC Potentiometer Application 3.1 Working Current Adjustment 3.2 Experimental Content 3.3 Laboratory Apparatus Ⅳ Discussion of Experimental Results Ⅴ FAQ Ⅰ Potentiometer Principle Analyses If you want to firmly acquire the use of the basic potentiometer, you must first understand its compensation principle and operational principle. 1.1 Compensation Principle The electromotive force (EMF) of the power supply is theoretically equal to the voltage of the two poles when there is no net current flowing inside the power supply. If you directly use a voltmeter to measure it, the result is actually the terminal voltage not the EMF. Because the power supply has internal resistance r0, if the voltmeter is directly connected in parallel to the two ends of the power supply, there must be a current I through the inside of it, and also there is inevitably a potential drop Ir0 inside. So the indicated value of the voltmeter is only the terminal voltage of the power supply (U=E-Ir0) size. Obviously, in order to be able to accurately measure the EMF of the power supply, the current I must be zero. At this time, the terminal voltage U of the power supply is equal to its electromotive force E. Figure 1. Closed Loop As shown in the figure on the right, connect the electromotive force as Es, Ex and galvanometer G to form a closed circuit. When Es<Ex, the current direction is as shown in the figure, and the pointer of the galvanometer is biased to one side. When Es>Ex, the direction of current is opposite to the direction shown in the figure, and the pointer of the galvanometer is biased to the other side. Only when Es=Ex, there is no current in the loop. At this time, i=0, and the pointer of the galvanometer is not deflected. We call these two electromotive forces in a compensation state. Conversely, if i=0, then Es=Ex, this method is called zero-show method. 1.2 Operational Principle As shown in the figure, the compensation principle shows that Ex can be determined by measuring Vab. The next step is how to accurately measure Vab. Here, the comparative measurement method is used. Connect Ex to the tap of Rab. When the tap is slid to position Rab, no current flows in G, then Ex=I*Rab, where current I is the main circuit current. Then connect a standard battery EN with known EMF in the circuit, when the tap slides to the position Rcd, G is 0 again, then EN=I*Rcd, where This method is to obtain the ratio relationship between the voltage to be measured and the EMF of the standard battery through the comparison of resistance. Because R is a precision resistance, Rab/Rcd can be read accurately, EN is a standard battery with high-accuracy EMF. Therefore, as long as the auxiliary power supply E is stable and the galvanometer G has sufficient sensitivity during the measurement process, Ex can have a very high measurement accuracy. The voltage measuring instrument made according to the above principle is called a potentiometer. Figure 2. Auxiliary Circuit It should be pointed out that the condition for the establishment of  is that the working current of the auxiliary circuit in the two compensations must be equal. In fact, in order to facilitate the reading, I=EN/Rcd should be standardized, so that the corresponding resistance value can be directly read out abV, which is Ex.Actually, there is no sliding rheostat in the instrument provided to us in the experiment, only 2 resistance boxes. This experiment requires us to use a rheostat box to replace the sliding rheostat. Therefore, we will use a resistor box R1 instead of the compensation method to measure the sliding rheostat RP, the other resistor box R2 acts as Rab. Since the resistance of them can be read directly, we can easily keep the current through the auxiliary circuit unchanged, that is, keeping R1+R2 constant.   Ⅱ UJ25 DC Potentiometer Overview UJ25 DC Potentiometer is a kind of high potential device, the upper limit of measurement is 1.911110V, the accuracy is 0.01 grade, and the working current I=0.1mA. Its principle is shown in the figure, the bottom of the right figure is its panel, and the functions of the upper 12 binding posts have been indicated on the panel. The Rab in the figure is two step resistance knobs, marked with the value of the standard battery EMF at different temperatures for correction when adjusting the working current. RP is used to adjust the working current I. Rcd is the six large knobs marked with voltage values, used to measure the unknown voltage value at the lower left corner of the function switch. When it is off, the potentiometer does not work; when it is at N, it can be connected to check and adjust the working current. When it is at X1 or X2, it can measure the unknown voltage of the first channel and obtain the second channel. The three buttons marked G0, G1, and short circuit are the control switches for rapid current detection. By being in the off state and pressing G0, the galvanometer is on in the circuit, but a large resistor R is connected in series to compensate for the principle. At the same time, protect the galvanometer; press G1 down, the galvanometer is directly connected to the circuit, so that the potentiometer is in a high-sensitivity working state. When the damping switch turns on, the galvanometer coil is short-circuited, and the coil does not swing due to the large electromagnetic damping. Figure 3. UJ25 DC Potentiometer Circuit   Ⅲ UJ25 DC Potentiometer Application 3.1 Working Current Adjustment Turn the function switch to N, turn the temperature compensation resistor Rab to the last two digits of the corrected standard battery EMF "1.018V", press the "G0" and "G1" respectively, and adjust RP to zero for the galvanometer.Measure the voltage to be measured.Switch the function switch to X1 or X2, press the "G0" and "G1" buttons respectively, and adjust Rcd to the galvanometer zero, finally the displayed value is the voltage to be measured. 3.2 Experimental Content 🔺Assemble Potentiometer(1) Design and connect the potentiometer circuit, the following is the standard battery temperature correction formula: (2) Standardize the working current, and measure the electromotive force of the dry battery.(3) Measure the sensitivity of potentiometer. 🔺UJ25 DC PotentiometerUse UJ25 box-type potentiometer to measure dry cell electromotive force. 3.3 Laboratory Apparatus ZX-21 resistance box (two), pointer galvanometer, standard battery, regulated power supply, dry battery to be tested, double pole double throw switch, UJ25 box type potentiometer.Data Processing and Error Quantitative Analysis.🔺Raw DataStandard battery electromotive force: E20=1.01186V, UJ25 measurement Ex=1.469285V, accuracy level 0.01Ambient temperature: T1=20.5℃, T2=21.5℃ EN R1=1018.6Ω R2=1983.8Ω EX R'1=1469.8Ω R'2=1532.6Ω Sensitivity Measurement/14div R''1=1484.1Ω R''2=1518.3Ω 🔺Potentiometer Measurement ResultsStandard Electricity Correction Value where ，get EN=1.01857VPosition battery EMF calculation 🔺Error and Uncertainty Analysis(1) Instrument Error get Similarly Knowing that R1, R2, R'1, R'2 are independent of each other, then the data in (1) can be obtained: (2) Sensitivity ErrorSensitivity  (3) Effects of the Temperature Change Assuming the temperature is constant, then Because of , therefore, this part of the error and its uncertainty can be ignored.(4) EN Stability Because of therefore, this part of the error and its uncertainty can be ignored.(5) Error Analysis and Synthesis of UncertaintyFrom the calculation of (3) and (4), it can be seen that the combination of uncertainty can omit the error of EN indication, and omit the error caused by the change of the auxiliary power supply and the standard battery EN during the two zero indications. Also the sensitivity error of the circuit during the two times of zero display, and because the readings of multiple measurements are almost unchanged. So only one measurement result is recorded and used, and we do not consider the impact of EN error on the measurement of Ex.Compared with the uncertainty of (2) obtained by (1), the uncertainty of (2) is about one-tenth of the uncertainty of (3), but considering that the uncertainty of (3) is of the order of 10^(-3), it can ignore the magnitude of 10^(-4). In the end , get the final result of the measurement.   Ⅳ Discussion of Experimental Results The use of UJ25 potentiometer can more accurately measure the electromotive force of the unknown power source, so as to further analyze the measurement results of the self-assembled potentiometer.Knowing that the measurement result of UJ25 potentiometer is EX=1.469258, and calculate the sensitivity error of the instrument: Because the readings of multiple measurements are consistent, it is ignored.That is, the actual measurement result of UJ25 potentiometer is .The measurement result is .That is, the relative error is .The operation of this experiment is relatively simple, but the data processing is slightly complicated, especially the calculation of uncertainty. Because of its many sources, it is impossible to analyze the errors one by one, so the smaller influencing factors are ignored to simplify the calculation. In this process, we understand that the principle of compensation to eliminate the internal resistance of the electric meter and the battery will be of great help to subsequent experiments.   Ⅴ FAQ 1. What is a potentiometer in a circuit?A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. ... Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. 2. What is the purpose of the potentiometer?A potentiometer is a type of position sensor. They are used to measure displacement in any direction. Linear potentiometers linearly measure displacement and rotary potentiometers measure rotational displacement. 3. How does a potentiometer affect a circuit?The potentiometer is a three-wire resistive device that acts as a voltage divider producing a continuously variable voltage output signal which is proportional to the physical position of the wiper along the track. 4. What happens when you turn potentiometer?It will behave like a normal resistor. When the circuit is connected to a center lead, and an outside lead, the potentiometer will behave like a variable resistor - turning the post of the potentiometer will increase (clockwise), or decrease (counter-clockwise) the resistance of the potentiometer. 5. How does a potentiometer change resistance?As you turn the knob of a potentiometer, the change in the resistance can be either linear or logarithmic. The way the resistance changes is called the taper. With a linear taper potentiometer, turning a knob a certain amount will change the resistance by a set amount, no matter the position of the knob. 6. How much voltage can a potentiometer handle?The easiest way to think about it is that there is a maximum current through the pot. If you have a 1W 100 ohm potentiometer, the max. current is 100mA (full voltage = 10V); if you are using only 27 ohms of the potentiometer then the max. 7. How does current flow in a potentiometer?Assume V to be the voltage produced by the cell in the primary circuit across the length of the potentiometer wire, and E to be that produced by the cell of the secondary circuit. 8. What is the formula for potentiometer?It is calculated as V/L, where V is the potential difference between two points and L is the distance between two points. Also K = (IρL/A)/L = Iρ/A. 9. How is potentiometer power calculated?Imax = √(P/R) where Imax is the maximum amount of current that can pass safely through any part of the pot, P is the specified power rating of the pot, and R is the specified resistance of the pot. For example, a 10,000-ohm, 1-watt potentiometer can safely pass √[1/(1 x 104)] amperes, or 10 milliamperes. 10. How do you calculate the output voltage of a potentiometer?Measure the total battery voltage, and then measure the voltage between the same two points on the potentiometer (wiper and negative side). Divide the potentiometer's measured output voltage by the measured total voltage. 11. What is the working principle of potentiometer?The principle of a potentiometer is that the potential dropped across a segment of a wire of uniform cross-section carrying a constant current is directly proportional to its length. The potentiometer is a simple device used to measure the electrical potentials (or compare the e.m.f of a cell). 12. What is potentiometer calculate the internal resistance of a cell?To calculate internal resistance, we use a potentiometer to first calculate the voltage across the battery, with no current through it. Then we attach a resistor in parallel to the battery and recalculate the voltage across it. ... Using the battery equation, we calculate the internal resistance. 13. What are the two uses of potentiometer?The applications (uses) of the potentiometer:Voltage divider: The potentiometer can be used as a voltage divider to change the output voltage of a voltage supply.Audio control: Sliding potentiometers are commonly used in modem low-power audio systems as audio control devices. 14. How do you calculate the emf of a cell using a potentiometer?Using a potentiometer, we can determine the emf of a cell by obtaining the balancing length l. Here, the fall of potential along the length l of the potentiometer wire is equal to the emf of the cell, as no current is being drawn from the cell. 15. How can potentiometer be used to calculate potential difference?A Potentiometer can be to measure e.m.f of a cell which cannot be measured by a voltmeter. When a voltmeter is connected in a circuit it draws current through the circuit and thus can measure the potential difference across the cell terminals. ... Thus it measures the e.m.f. of the cell. 16. What is the principle of potentiometer support with equation?The basic potentiometer working principle is based on the fact that the potential across any piece of the wire is directly proportional to the length of the wire, which has a uniform cross-sectional area and the constant current flowing through it. 17. What is potentiometer write its principle and construction?The potentiometer is a device used to compare the e.m.f of two cells. It works on the principle that when a constant current flows through a wire of uniform cross-sectional area, a potential difference between its two points, is directly proportional to the length of the wire between the two points.

Introduction The transistor is a current-control device. For example, control the collector-emitter current by changing the base current. In a general voltage amplification occasion, this amplification effect comes from the use of resistors to convert current into voltage. In the small-signal model, the source of the base current is the ratio of the input voltage to the base-emitter dynamic resistance rbe, which is usually kΩ. So the base current is very small, and may only be a few tenths of mA. Through the amplification of the transistor, the base current is generated between the collector and the emitter by β times. This article will introduce how transistor works in the common-emitter amplifier circuit. Transistor Amplifiers Circuit Introduction Catalog Introduction Ⅰ Common-emitter Amplifier Circuit Formula Ⅱ Common-emitter Amplifier Circuit Design 2.1 Design Steps 2.2 Circuit Analysis 2.3 Common-emitter Circuit Design 2.4 Circuit Performance Parameters Ⅲ Common-emitter Amplifier Circuit Expansion 3.1 Increase Magnification 3.2 Low-voltage and Low-loss Circuit 3.3 Differential Output Circuit 3.4 Filter and Tuning Amplifier Circuit Ⅳ Summary Ⅴ FAQ Ⅰ Common-emitter Amplifier Circuit Formula Here, take the common emitter amplifier circuit as an example: Figure 1. Transistor Common-emitter Amplifier Circuit △Vo=VCC-△ieRc=VCC-β△ibRc=VCC-△Vi·Rc/rbe△Vi/rbe=△ibThus, the collector generates a current of β times ib:△ie=β△ibFurthermore, the output voltage can be obtained by the relative positive power supply potential:△Vo=VCC-△ieRc=VCC-β△ibRc=VCC-△Vi·Rc/rbeThus, we can get an inverted amplified voltage signal by AC coupling and controlling the collector resistance Re. But generally the emitter will have a resistance to control the gain, so the above formula is not practical. When designing a circuit in non-extreme situations, we often hope that the circuit can work with most general-purpose transistors, avoiding the parameter that depends on component parameters such as rbe. At the same time, it is very cumbersome to consider the base current in the specific calculation. Therefore, in the general design process, the existence of the base current is ignored in an approximate calculation (In some circuits, although the base current is ignored, it is still necessary to give the base a certain current drive to make the circuit working normally). In addition, the calculation of gain is the external circuit resistance not the rbe.Among them, the base-emitter tube voltage drop VBE is also a very important parameter, which is generally equal to 0.6V (silicon tube). The parameters of the transistor circuit can all be obtained according to VBE=0.6V and Ohm's law.The cumbersome part of the transistor circuit lies in the setting of the static operating point. Usually, careless design will cause clipping and distortion of the output waveform. Therefore, the selected values of some experimental values can be used for reference. The overall design idea is: quantitatively determine the voltage and current to calculate the resistance.   Ⅱ Common-emitter Amplifier Circuit Design The common-emitter amplifier circuit is a typical inverting amplifier, which has a wide range of applications and stable effects. First show the overall design ideas, and then explain the purpose and principles of the design in steps. 2.1 Design Steps 1) Determine the supply voltage VCC, and determine the static emitter current IE according to the frequency curve/noise curve/others.2) Determine VE, where selects 1~2V to absorb temperature drift.3) According to VE and IE, calculate the emitter static resistance RE ( IE≈IC).4) Determine the magnification Av, and apply the relationship Av=RC/RE to calculate the static collector resistance RC. At this point, the static working point has been established.5) Check whether the static operating point meets the requirements: positive output swing limit=VCC-IE·RC, negative output swing limit=IE·RC-VE. It is necessary to ensure that the amplified output voltage does not exceed the swing limit (usually the swing limit is larger). If RC is too large, there will be a downside clipping, so is the small RC. In addition, determine whether the power exceeds the limit: PC=VCE·IC.6) Determine the base bias voltage as follows: According to VBE=0.6V, it is easy to get VB=VE+0.6 (divide the voltage from the power supply through the resistor). Since ib is considered to be small and negligible, the current IB0 flowing through the base voltage divider resistors (R1, R2 in the above figure) should be much larger than ib. ib is approximately calculated as IC/β, and IB0 is about an order of magnitude larger than ib, so R2=VB/IB0, R1=(VCC-VR2)/IB0.7) Finally, determine the AC coupling capacitor value and the power supply decoupling capacitor value.Let's first use a designed common-emitter amplifier circuit to intuitively understand the waveforms of the next parts: Figure 2. Transistor Common Emitter Amplifier Circuit Design As shown in the figure, the circuit uses 2SC2240 tube, 15V power supply, and the input and output are AC coupled. The output signals are as following:  Figure 3. 4-channel Signal Waves The pale blue waveform is the input signal, selecting the sine wave of 1kHz, 1Vpp.The green is the output signal, amplified by about 5 times, and it is inverted.The blue is the base signal, which can be seen because the DC level is raised due to the influence of the base bias resistance.The red is the emitter signal, which is only a fixed value away from the base signal.   2.2 Circuit Analysis First, perform a DC analysis, that is, determine the static operating point. In the initial design process, the design and verification of static operating points are also the first to proceed. The static potential of the base can be easily calculated according to the base bias resistance, and the static potential of the emitter can be determined according to the voltage drop of the base-emitter tube as a constant. Therefore, according to the magnitude of the emitter resistance, the magnitude of the collector-emitter current can be obtained, and then the collector static potential can be obtained from the power supply voltage.Why is the static operating point important? Take the NPN transistor as an example, which is equivalent to two back-to-back diodes. If requiring the diode work, you must give it a proper bias to make it reasonably conductive. In the circuit, the base-collector diode prevents internal feedback, and the base-emitter diode is the key to achieving amplification. In other words, it is enough to design an external circuit so that the current flows normally in the base-emitter diode. This idea will be mentioned in the analysis of the carrying capacity of the emitter follower.Find the AC voltage gain. When the input voltage changes △vi, it will cause the emitter current to produce an AC change △ie. Since the base emitter voltage drop is constant, it does not contribute to the AC change, so △ie=vi/RE. Therefore, the emitter AC output voltage can be determined as vo=△ieRC=vi·RC/RE, and the AC gain is Av=RC/RE. This conclusion can quickly analyze the magnification of the common-emitter circuit.The output power rails are VCC and VE respectively, which are determined by the current characteristics of the transistor during operation, and there is generally no rail-to-rail output. According to the output power rail and the AC amplification factor, the circuit can be used.When the input and output are not AC coupled, the input (especially for DC) will cause the output waveform to be distorted.   2.3 Common-emitter Circuit Design After understanding the circuit characteristics, you can design the common emitter circuit according to the design steps at the beginning of this section. The static operating point and magnification have been determined during the analysis, and the other parts are designed below.Supply voltage: According to the swing of the output voltage, we can determine the size of the voltage. Usually the power supply voltage is larger than the output peak-to-peak value.Transistor: Select the appropriate transistor according to the operating frequency, required power, noise level and β, etc.Emitter current: Determine the size of the emitter current according to the frequency characteristics by consulting the device manual.RC and RE: Determined by the emitter voltage and current, and the magnification, pay attention to review the upper and lower limits of the swing and the rated power.Base bias resistance: VB is determined according to VE, thereby determining the voltage divider resistance of the power supply. Note that the current flowing through the voltage divider resistor should be one to two orders of magnitude higher than the base current. The base current is calculated by dividing the collector-emitter current by β.Coupling capacitor: The AC coupling capacitor is generally 10uF. Note that the coupling capacitor of the output stage and the input impedance of the next stage will form a high-pass filter. The cutoff frequency of the filter should be handled carefully.   2.4 Circuit Performance Parameters Through the method of AC analysis, we can obtain some characteristic parameters of the designed circuit, such as input and output impedance, magnification and so on.Input impedance: According to AC analysis, the input impedance is the parallel value of the base bias resistance. In small signal analysis, the base emitter dynamic resistance rbe should also be connected in parallel.Output impedance: The method to determine the output impedance is to add a load to the circuit. When the peak-to-peak output value drops to half of the no-load, the load impedance is the output value. Generally, the output impedance of the common-emitter amplifier circuit is the collector resistance RC.Magnification: Due to the influence of the base current, the actual magnification is about 10% lower than the design value. So the design formula is more practical.   Ⅲ Common-emitter Amplifier Circuit Expansion By improving the general common-emitter amplifier circuit, various application circuits with other characteristics can be obtained. This section introduces the means to increase the magnification, the low-voltage power supply circuit, the differential output circuit, and the tuning amplifier circuit. 3.1 Increase Magnification According to the introduction of the design circuit, the voltage gain is mainly determined by the ratio of the collector resistance RC to the emitter resistance RE. So it is common to change the ratio of the resistance to change the gain. However, the problem arises: these two resistors are responsible for determining the working current at the same time. Because the DC operating point is changed arbitrarily, the circuit is likely to be distorted or even not work.From another perspective, voltage gain belongs to the category of "AC Analysis", and the static operating point belongs to "DC Analysis". So add some reactive components to the circuit to change the ratio under the AC perspective, the resistance value during DC analysis does not change.This can be achieved by connecting the emitter resistor in parallel, or making the resistor in parallel with the capacitor, that is, modifying the circuit in the first section: Figure 4. Common-emitter Amplifier Circuit Pay attention to the emitter in the above figure. In the AC analysis, the resistor R4 is short-circuited by the capacitor. At this time, it is equivalently considered that the emitter resistor is only R7 (330Ω). From the signal source and the oscilloscope, the signal has been amplified nearly 50 times at this time. It is much larger than the original design value (10k/2k=5), thus realizing the expansion of voltage gain. If the original emitter resistance is not split, but the entire capacitor is connected in parallel, the maximum gain βRC/rbe will be obtained at this time.How to choose the capacitance value? It should be noted that after the capacitors are connected in parallel, the entire circuit will have high-pass characteristics, and the cut-off frequency is f=1/2πRC. If this high-pass characteristic is not required, the C capacitance value can be selected to a larger value between 47uF~100uF.In addition, the capacitor C6 has the function of temperature compensation. 3.2 Low-voltage and Low-loss Circuit If the op amp circuit is powered by a dry battery (1.5V), it is not realistic, but the transistor circuit can be done. The key is to use the conduction voltage drop of the external diode to offset the base-emitter voltage and have small small. The circuit in the figure below can still amplify small signals as designed even under 1.5V power supply: Figure 5. Common-emitter Amplifier Circuit But the disadvantage is that the maximum voltage of the system is always below the supply voltage. Because of the small circuit loss, it is suitable for low power consumption. 3.3 Differential Output Circuit Fully differential op amps can provide dual-mode output, and many transmission lines also require differential transmission. Transistor circuits can also perform differential output. In addition to the principle of a common emitter amplifier circuit, the principle of an emitter follower is also used. The following figure shows the circuit connection of the differential output. Figure 6. Common-emitter Amplifier Circuit It can be seen that two differential signals with the same shape and opposite phase are output. The collector signal is in phase with the input signal, and the emitter output signal is in phase with the input signal. However, the output impedance of the two signals is different due to the different lead-out positions. The output impedance of the inverted output is higher (RC), and the output impedance of the non-inverted output is lower, which is suitable for driving the load. The inverted output is generally connected to the emitter follower before driving.In addition, the static potential of the base should be set between VCC and GND as much as possible to expand the undistorted output range.   3.4 Filter and Tuning Amplifier Circuit The introduction of reactive components in the circuit will cause the properties of the circuit to change with the frequency. We can use this property to design LPF, HPF, and tuning amplifier commonly used in high-frequency circuits. Actually, it uses the characteristic that the impedance of the reactance element changes with the frequency, and then changes the voltage gain at the current frequency. The impedance at the resonance frequency is often purely resistive and has an extreme value to achieve frequency selective amplification. The following show low-pass, high-pass and frequency selective amplifiers at specific frequencies:① LPF Figure 7. Common-emitter Amplifier Circuit As shown in the figure, a low-pass filter is constructed (the input of the bode tester is placed at the base instead of the output of the signal generator, because the input coupling capacitor will form a high-pass filter with the input resistor, which affects the observation effect), and its cut-off frequency is about 1.06kHz, calculated by f=1/2πRcC.From the sinusoidal steady-state analysis, the impedance of the RC parallel loop is R/√(1+(wRC)^2). As the frequency increases, the impedance decreases, so the voltage gain decreases, forming a low-pass characteristic.② HPF Figure 8. Common-emitter Amplifier Circuit As shown in the figure, a high-pass filter is constructed, and the calculation of its cut-off frequency is similar to that of LPF.At the gain peak point, the voltage gain reaches 50dB, which is close to the β value of the transistor. Then the gain is attenuated due to the deterioration of the transistor's frequency characteristics.③ 10.7MHz Figure 9. Common-emitter Amplifier Circuit By replacing RC with an LC network with a resonance frequency of 10.7MHz, a frequency selective amplifier can be obtained. As shown in the figure, the amplification factor is 35dB at 10.7M, while the amplification factor when detuning 1MHz is only 12.6dB. The disadvantage is that the pass-band is slightly wider, the rectangular coefficient is not good enough, and the equivalent quality factor of the loop is about 65.2, which is relatively large. In addition, the high-frequency decoupling capacitor has been changed to 1uF. Resonant Amplifier Circuit Example: Figure 10. Resonant Amplifier Circuit Example   Ⅳ Summary Transistor amplifier circuit is the basis of an operational amplifier circuit, and common-emitter configuration is the most commonly used form. Drawing lessons from the feature that the amplifier's magnification can be easily determined by the ratio of two resistors, and the gain of the common emitter amplifier can also be approximated by the ratio of the two resistors.   Ⅴ FAQ 1. What are transistor amplifiers used for?Amplifiers are derived from the transistors because they are capable of operating under three regions active, cut-off and saturation. For the purpose of amplification, the focus will be on the active region. The main purpose of these amplifiers is to enhance the strength of the applied input signal without alteration. 2. How does a transistor amplify current?Transistors are normally used as amplifiers. ... The small current travels from the voltage source into the base of the transistor. A current at the base turns on the transistor. The current is then amplified and travels from the emitter of the transistor to the collector. 3. What is a common emitter transistor amplifier?The common emitter amplifier is a three basic single-stage bipolar junction transistor and is used as a voltage amplifier. The input of this amplifier is taken from the base terminal, the output is collected from the collector terminal and the emitter terminal is common for both the terminals. 4. Why common emitter is used in amplifier?Common emitter (CE) configuration. ... Common emitter transistors are used most widely, because a common emitter transistor amplifier provides high current gain, high voltage gain and high power gain. This type of transistor gives for a small change in input there is small change in output. 5. What is the use of CE amplifier?In electronics, a common-emitter amplifier is one of three basic single-stage bipolar-junction-transistor (BJT) amplifier topologies, typically used as a voltage amplifier. It offers high current gain (typically 200), medium input resistance and a high output resistance. 6. How does transistor work as amplifier?A transistor acts as an amplifier by raising the strength of a weak signal. The DC bias voltage applied to the emitter base junction, makes it remain in forward biased condition. ... Thus a small input voltage results in a large output voltage, which shows that the transistor works as an amplifier. 7. What is common emitter amplifier circuit?The Common Emitter Amplifier circuit has a resistor in its Collector circuit. The current flowing through this resistor produces the voltage output of the amplifier. ... The Base of the transistor used in a common emitter amplifier is biased using two resistors as a potential divider network. 8. What are the main parts of a transistor amplifier circuit?A Single stage transistor amplifier has one transistor, bias circuit and other auxiliary components. The following circuit diagram shows how a single stage transistor amplifier looks like. When a weak input signal is given to the base of the transistor as shown in the figure, a small amount of base current flows. 9. What is the phase difference in common emitter amplifier?The phase difference between the input and output voltage of CE amplifier circuit is. The phase difference of 1800 between the signal voltage and output voltage in a common emitter amplifier is known as phase reversal. 10. When an NPN transistor is used as an amplifier?For a npn transistor to be used as an amplifier, forward bias has to be applied on the transistor. Thus, when an npn transistor is used as an amplifier, holes move from base to emitter. So, the correct answer is option D i.e. holes move from base to emitter. 11. When an NPN junction transistor is used as an amplifier in CE mode?A transistor is used in the common emitter mode as an amplifier then: (A) the base emitter junction is forward baised. (B) the base emitter junction is reverse baised. (C) the input signal is connected in series with the voltage applied to bias the base emitter junction. 12. How is an NPN transistor used as an amplifier show with its circuit diagram?The circuit of a common-emitter amplifier using an n-p-n transistor is shown below : In a common emitter amplifier circuit, the input signal voltage and output collector voltage are in opposite phase. i.e 180° out of phase. Thus the phase difference between the input signal and output voltage is 180°. 13. How does a common emitter amplifier work?Operation of Common Emitter AmplifierWhen a signal is applied across the emitter-base junction, the forward bias across this junction increases during the upper half cycle. This leads to an increase in the flow of electrons from the emitter to a collector through the base, hence increases the collector current. 14. What is β for a CE configuration?Base Current Amplification Factor (β)The base current amplification factor is defined as the ratio of the output and input current in a common emitter configuration. In common emitter amplification, the output current is the collector current IC, and the input current is the base current IB. 15. What is current gain CE configuration?The current gain of a transistor in CE configuration is defined as the ratio of output current or collector current (IC) to the input current or base current (IB). The current gain of a transistor in CE configuration is high. Therefore, the transistor in CE configuration is used for amplifying the current.