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Introduction Diodes are widely used in electronics, such as rectification in power supply, as detection and mixing, etc. in communications, and are often used in voltage regulation and protection in various circuits (such as freewheeling diodes, TVS and so on). Due to the wide variety and versatility, the following is an analysis of the simple application of Schottky diodes in digital circuits.In this video, the Schottky diode has been explained.CatalogIntroductionⅠ Schottky Diodes CharacteristicsⅡ Schottky Diode Applications2.1 As Dual Power Supply2.2 As AND Gate2.3 As OR GateⅢ Schottky Diode ParametersⅣ Example AnalysisⅠ Schottky Diodes CharacteristicsThe Schottky diode is structurally different from the PN junction diode. It is made of an anode metal (a barrier layer made of a material such as molybdenum or aluminum), SiO2 (electric field eliminating material), and N- epitaxial layer (arsenic material), the N-type silicon substrate, N+ cathode layer, and the cathode metal, which are as shown in the following figure. A Schottky barrier is formed between the N-type substrate and the anode metal. When a forward bias is applied to both ends of the Schottky barrier (anode metal is connected to the positive electrode of the power supply, and the N-type substrate is connected to the negative electrode), the Schottky barrier layer is narrowed, and the internal resistance becomes small. On the contrary, when a reverse bias is applied across the Schottky barrier, it becomes wider and its internal resistance becomes larger. Figure 1. Schottky Diode Structure Ⅱ Schottky Diode ApplicationsThe problem with Schottky diodes is that the withstand voltage is relatively low and the reverse leakage current is large. At present, the general condition of the Schottky diode used in the power conversion circuit is that the withstand voltage is below 150V, the average current is below 100A, and the reverse recovery time is between 10 and 40ns. Therefore, Schottky diodes are ideal device for use in high frequency and low voltage circuits.2.1 As Dual Power SupplyAt present, in the electronic design with the main controller, the real-time clock (RTC) is basically used, and the RTC needs an additional button battery to support, to avoid information lost after the system is powered off. And meanwhile, after the system is started, in order to extend the battery life, the main system is often supplied with power. Therefore, RTC often requires dual power supply, and the diode can be used for power isolation due to its single-conductivity. Taking the small-signal Schottky diode BAT54C as an example, the forward voltage drop is only 0.24v (the forward current is 0.1mA), and the RTC current consumption is uA-level, after adding the Schottky diode to isolate power supply to save info security.2.2 As AND GateAs shown in the figure below, n Schottky diodes form the AND gate of the n input. As long as there is a signal output logic 0 in A1~An, the Output is logic 0, only all signals in A1~An output logic 1, Output can output logic 1. That is, the phase sum of the signals A1~An is realized. Since the chip signal input stage is basically high-resistance in the digital circuit, the overall current of the AND gate circuit composed of the Schottky diode is uA-level, and the Schottky diode voltage drop is extremely small. In the case of it, the flat can still meet the design requirements.  Figure 2. Schottky Diode as AND Gate2.3 As OR GateAs shown in the figure below, n Schottky diodes form an n-input OR gate. As long as there is a signal output logic 1 in A1~An, Output outputs a logic 1. Only all signals in A1~An output logic 0, and Output can output logic 0. That is, the phase sum of the signals A1~An is realized.  Figutre 3. Schottky Diode as OR Gate Ⅲ Schottky Diode ParametersNote: Because Schottky diodes are used differently in different electronic circuits, we also need to consider the following parameters when using them.1）Forward voltage drop VFVF is the forward voltage drop when the diode is forward conducting. The greater the current through the diode, the larger the VF, in addition, the higher the diode temperature, the smaller the VF.2）Reverse saturation drain current IRIR refers to the current flowing through the diode when a reverse voltage is applied to the diode. The Schottky diode has a large reverse leakage current, therefore, selecting a Schottky diode with a smaller IR.3）Rated current IFIt refers to the average current value calculated from the allowable temperature rise when the diode is in a long time operation.4）Maximum surge current IFSMExcessive forward current that is allowed to flow. It is not a normal current, but an instantaneous current, which is quite large.5）Maximum peak inverse voltage VRMEven if there is no reverse current, as long as the reverse voltage is continuously increased, the diode will be damaged sooner or later. This reverse voltage is not the instantaneous voltage, but the reversed voltage that is added repeatedly. Since the rectifier is supplied with an alternating voltage, its maximum value is a specified important factor. And the maximum reverse peak voltage VRM refers to the maximum reverse voltage that can be applied to avoid breakdown. At present, Schottky's highest VRM value is 150V.6）Maximum DC reverse voltage VRVR is the value when the DC voltage is continuously applied. For DC circuits, the maximum DC reverse voltage is important to determine the allowable and upper limits.7）Maximum operating frequency FMDue to the junction capacitance of the PN junction, when the operating frequency exceeds a certain value, its unidirectional conductivity will deteriorate. And Schottky diodes have high FM values up to 100 GHz.8）Reverse recovery time TrrWhen the operating voltage changes from a forward voltage to a reverse voltage, the ideal operation of the diode is that the current can be instantaneously turned off. In fact, it usually takes a little delay. The amount that determines the current cut-off delay is the reverse recovery time. Although it directly affects the switching speed of the diode, it does not mean that this value is small. That is, when the diode is suddenly reversed by conduction, the reverse current is greatly attenuated to a time required to approach IR. This indicator is important when the high-power switch is operating in the high-frequency state.9）Maximum dissipation power PWhen a current flows through the diode, it absorbs heat and raises its temperature. In reality, the external heat dissipation condition also has a great influence on P. Specifically, the voltage applied across the diode is multiplied by the current flowing through and the reverse recovery loss. Schottky Diode Symbols Ⅳ Example AnalysisIn digital circuit design, it is often necessary to make simple phase, or phase inversion of some signals. If the logic chip such as the 74 series is directly used, not only the layout area is greatly increased, but also the wiring is not flexible. The use of small-signal Schottky diodes and OR gates is more flexible and easy to use. The following figure shows a simple two-way reset circuit. JTAG generating a reset signal needs to reset the master, and the external reset button also needs to reset the master when pressed. If the JTAG reset and button reset directly to the reset pin of the master, it may cause damage to the JTAG emulator. For example, when the reset button is pressed, the JTAG output reset pin will be directly lowered. The phase and circuit are formed by the Schottky diode BAT54A , and the signal outputs do not affect each other. The following figure allows the master to reset as long as the JTAG output logic 0 or pressing the button reset output logic 0.Figure 4. Schottky Diode BAT54A ApplicationIf it is to be used as a non-gate, a triode can be used. Of course, the triode is widely used in electronics, such as a switching device in a digital circuit, as a current drive, level shifter, and the like. Frequently Asked Questions about Small Signal Schottky Diodes1. What is the Schottky diode and how it works?A typical diode combines p-type and n-type semiconductors to form a p-n junction. In a Schottky diode metal replaces the p-type semiconductor. This metal can range from platinum to tungsten, molybdenum, gold, etc. When metal is combined with an n-type semiconductor an m-s junction is formed. 2. What does small signal mean?A small signal is an AC signal (more technically, a signal having zero average value) superimposed on a bias signal (or superimposed on a DC constant signal). This resolution of a signal into two components allows the technique of superposition to be used to simplify further analysis. 3. Which statement is correct for Schottky diode?Explanation: The majority charge carriers in a Schottky diode are electrons not holes. Explanation: Due to the metal-silicon junction there are no stored charges hence, no reverse recovery time, due to which the switching is faster. 4. What are the two important features of a Schottky diode?We have seen here that the Schottky Diode also known as a Schottky Barrier Diode is a solid-state semiconductor diode in which a metal electrode and an n-type semiconductor form the diodes ms-junction giving it two major advantages over traditional pn-junction diodes, a faster switching speed, and a low forward bias.

DescriptionIt's not weird to discover that applications are becoming more complex,with connectivity just one of the drivers. And,as it become more complex.the number of sensors grows,as does the need for more capable user interfaces. At the same time,algoriths need more processing power,wireless stacks mandate larger memories and power budgets are shrinking.In order to coping with the growing list of demands, a great number of leading MCU manufacturers have recently launched Micro Controller Unit built around the ARM Cortex-M4 core. BodyThe M3 is general purpse and the M0+is low cost but the M4 is a more capable core in general if look at the Cortex range. Oivind Loe,a senior strategic marketing manager with Sillicon Laboratories said. Microchip's product marketing manager--Anand Rangara commented:“Something that sat around without the need to communicate now needs connectivity. When that happens, you need more flash and RAM, as well as graphics capability and perhaps the ability to support a touch interface. All this has to be offered at good power/performance and an attractive price.”  'Industrial Strength' MCUsSilicon Labs has expanded its EFM32 Gecko portfolio with what it calls ‘industrial strength’ MCUs. It says the EFM32GG11 Giant Gecko MCU family offers the ‘most advanced’ feature set available in the low-power MCU market.Loe noted that MCU development isn’t just about power. “It’s also about executing tasks efficiently. A simple program with a few clocks will run efficiently on an M0+ core. But if the workload is larger, the M4 core has some special instructions that can allow it to use less energy than the M0+ and more efficiently than some larger cores – and that's crucial for a range of application.” GG11 Geckos offer up to 2Mbyte of flash and 512kbyte of RAM to accommodate more code and comms stacks, such as a 10/100 Ethernet MAC and a dual CAN interface. Looking to meet power budgets, the parts boast an active power consumption of 77μA/MHz, while drawing 1.6μA in deep sleep mode. FPU to Increase System EffiencyMicrochip’s SAM D5x/E5x MCUs also take advantage of the Cortex-M4’s floating point unit (FPU) to increase system efficiency. Running at up to 120MHz, the D5x and E5x MCUs come with up to 1Mbyte of dual-panel flash and up to 256kbyte of SRAM. Rangarajan noted: “We’ve listened to our customers, so we’ve included more connectivity in these MCUs. But it's not just about adding memory , it’s also about more performance and the ability to provide more flexible peripherals, interfaces and connectivity options.” Meanwhile,he  pointed out that the original SAM D MCUs – developed by Atmel prior to its acquisition by Microchip – were based on the Cortex-M0+. “But we’ve always wanted to take the product line to the next level of performance. This allows Microchip to address a broader range of consumer and industrial automation applications.” Limited the Clock RateBucking the trend to a certain extent, both Silicon Labs and Microchip have limited the clock rate in their latest MCUs. Giant Geckos, for example, have a maximum clock of 72MHz. “These products are focused on energy efficiency,” Loe claimed. “If you build an MCU to run at 200MHz, for example, then each clock cycle will consume more energy than in an MCU running at 72MHz. A lot of MCUs will be used in battery powered apps, so we need to be energy efficient and to enable the CPU to sleep a lot.” Rangarajan agreed that clock rate is not always the primary factor when it comes to developing MCU portfolios. “We hear our customers saying don’t give me faster clock rates, make sure the MCUs meet my requirements. An app that runs from a battery requires a power efficient MCU. If you want a fast MCU, then you have to make trade offs.” In Loe’s views, MCU selection is all about the ability to perform certain tasks at a particular power efficiency. “That is always going to involve trade offs, but an M4 based MCU will generally be good for embedded applications with challenging energy consumption requirements.” Adopt the Concept of Smart PeripheralsBoth companies have adopted the concept of smart peripherals in their recent products. Loe explained: “Twenty years ago, most MCUs saw the CPU doing everything. That took a lot of CPU cycles, which meant you couldn’t do as much as you might have liked.“Today, most apps will take advantage of DMA, which offloads the CPU. In turn, this allows the CPU to do more.” Rangarajan said Microchip provides what he called ‘sleepwalking’ peripherals. “If there’s a requirement for them to do small numbers of transactions, this can be done without waking the CPU.” On the other hand,Sillicon Loe Noted that It’s all about when you have to wake up the M4 core. We’re trying to allow it to sleep for as much as possible. More than half of the peripherals in a Giant Gecko can run autonomously in deep sleep mode. Both Companies are Keen to Highlight Their Provision Silicon Labs has launched a starter kit to support Giant Gecko based application development(following picture) With this approach, a Giant Gecko’s A/D converter can operate while the CPU is in deep sleep mode. “It can sample and use DMA to pull the data into RAM,” Loe continued.Loe highlighted a couple of aspects. “We have included a cyrotimer that runs in shut off; the lowest energy mode. It’s a simple timer that’s useful when you need the CPU to be asleep for minutes. there’s the Peripheral Reflex System, which allows peripherals to talk. For example, the real time clock could tell the A/D converter to take a sample. It gives a level of determinism which you don’t get from a CPU.  Microchip's Product brings better power efficiency How does an MCU developer differentiate their products from similar devices with an M4 core? Rangarajan pointed to the integration of a buck regulator. “This brings better power efficiency,” he claimed, “which means lower active power consumption; as little as 65µA/MHz. The parts also support flexible pin options.”“We’re offering the best integrated security features,” Rangarajan contended. “SAM Dx/Ex MCUs have crypto hardware acceleration – symmetrical and asymmetrical – and public key encryption, amongst other features. It’s something Microchip has taken to heart and has made sure it’s all in the MCU.“We’re offering the best integrated security features,” Rangarajan contended. “SAM Dx/Ex MCUs have crypto hardware acceleration – symmetrical and asymmetrical – and public key encryption, amongst other features. It’s something Microchip has taken to heart and has made sure it’s all in the MCU.  EndLoe pointed to the security management unit (SMU) as an ‘upgrade’ to the memory protection unit (MPU) associated with the M4’s core. “While the MPU allows you to segment memory into eight regions, the SMU takes that further. The MPU is restricted to eight regions, so there is limited granularity. The SMU allows you to selectively say which pieces of code can access each peripheral.” “All of this is important,” Rangarajan concluded, “as security will become standard in the next few years.”