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IntroductionA clamper circuit is an electronic circuit that shifts the DC level of a signal to a desired level without changing the shape of the applied waveform. Unlike clipper circuits that cut or limit portions of a signal, clampers preserve the entire waveform while repositioning it vertically on the voltage axis. This is achieved by fixing a specific part of the pulse signal (such as the positive or negative peak) at a specified voltage value while maintaining the original waveform shape unchanged.What is a Clamper Circuit?Ⅰ Clamper Circuit ApplicationsClamper circuits are widely used in various electronic systems and display devices. Key applications include:Television Systems: Clamper circuits restore the DC component of video signals and maintain the synchronization pulse at a fixed voltage level, ensuring stable image positioning and proper sync signal separation.Oscilloscopes and Test Equipment: Used to stabilize waveform display by fixing reference levels, preventing image drift caused by varying scanning speeds or DC component loss.Radar and Sonar Systems: Employed to maintain consistent signal levels for accurate detection and ranging.Amplifier Protection: Protects sensitive amplifier input stages from excessive DC offset voltages.Power Supply Circuits: Helps in voltage regulation and transient suppression.Communication Systems: Restores DC levels in signal transmission and reception circuits.Digital Logic Circuits: Provides voltage level shifting between different logic families.A basic clamper circuit comprises a capacitor, a diode, and a resistor. More sophisticated designs may include additional components such as bias voltage sources. In the following sections, we will explore different types of diode clamper circuits and compare their characteristics and performance.Ⅱ Diode Clamper Circuit2.1 Why Use Diode Clamper Circuits?While diode clipper circuits limit or cut the amplitude of waveforms, many applications require preserving the complete waveform while shifting its DC level. Clamper circuits fulfill this requirement by shifting the signal vertically to position its peak value at a desired level without distorting the original waveform shape.A diode clamper circuit utilizes the relatively stable forward voltage drop of the diode (typically 0.6-0.7V for silicon diodes or 0.2-0.3V for Schottky diodes) and its low reverse leakage current characteristics. These properties enable the circuit to clamp the potential at specific points and maintain the peak or trough of periodically changing waveforms at predetermined DC levels.Dual-Diode Clamper Protection: In protection applications, two diodes connected in reverse parallel configuration provide bidirectional clamping. Only one diode conducts at any given time while the other remains in the off state. This arrangement limits both positive and negative voltage excursions to approximately ±0.6V (for silicon diodes), effectively protecting sensitive circuit components from overvoltage conditions and electrostatic discharge (ESD).2.2 Diode Clamper Circuit TypesDiode clamper circuits are classified into two main categories: positive clampers and negative clampers. Each category includes both simple (unbiased) and biased variants.✅ Diode Positive ClamperOperating Principle:Positive Half Cycle: The diode is reverse-biased (OFF), acting as an open circuit. The capacitor charges to the peak input voltage Vi through the load resistor.Negative Half Cycle: The diode becomes forward-biased (ON), acting as a short circuit. The capacitor maintains its charge, and the output voltage Vo ≈ 0V (or slightly positive due to diode forward voltage drop).According to Kirchhoff's voltage law, the output waveform can be calculated for both positive and negative cycle conditions.(1) Simple Positive Clamper (Unbiased)Figure 1. Simple Positive Clamper CircuitOperation:When Vi is in the negative half cycle: D → ON, capacitor C charges to voltage V (negative on left plate, positive on right plate), Vo ≈ 0V.When Vi is in the positive half cycle: D → OFF, Vo = VC + Vi = 2V (assuming input amplitude is V).(2) Biased Positive ClamperFigure 2. Biased Positive Clamper CircuitSimple Method to Determine Output Waveform:The reference point of the output waveform on the voltage axis is determined by the bias voltage V1.The diode orientation determines the direction of waveform shift. If the diode points upward , the waveform shifts upward; if it points downward , the waveform shifts downward.After determining the reference point and direction, sketch the original waveform on the output coordinate axis using the reference point as the baseline to obtain the clamped output waveform.↪️ Diode Positive Clamper Circuits Comparison:Figure 3. Positive Clamper Circuits Comparison✅ Negative Clamper Circuit(1) Simple Negative Clamper (Unbiased)Figure 4. Simple Negative Clamper CircuitOperation:When Vi is in the positive half cycle: D → ON, capacitor C charges to voltage V (positive on left plate, negative on right plate), Vo ≈ 0V.When Vi is in the negative half cycle: D → OFF, Vo = -(VC + |Vi|) = -2V (assuming input amplitude is V).(2) Biased Negative ClamperFigure 5. Biased Negative Clamper CircuitOperation:When Vi is in the positive half cycle: Diode D → ON, capacitor C charges to voltage V (positive on left plate, negative on right plate), Vo = +V1 or -V1 (depending on bias polarity).When Vi is in the negative half cycle: Diode D → OFF. With a sufficiently large RC time constant, Vo = VC + Vi (negative half cycle) ≈ -2V + bias voltage.↪️ Diode Negative Clamper Circuits Comparison:Figure 6. Negative Clamper Circuits Comparison✅ Key Design ConsiderationsDiode Orientation: The direction of the diode determines whether the waveform shifts upward (positive clamping) or downward (negative clamping).Bias Voltage: The bias voltage establishes the reference point (baseline) of the clamped waveform on the voltage axis.RC Time Constant: The product of capacitance (C) and load resistance (R) must be sufficiently large—typically RC ≥ 10T, where T is the period of the input waveform. This ensures the capacitor maintains its charge between cycles, preventing droop and maintaining clamping accuracy.Diode Selection: Choose diodes with low forward voltage drop (Schottky diodes for precision applications) and fast recovery time for high-frequency signals.Capacitor Selection: Use capacitors with low leakage current (film or ceramic types) to maintain charge stability.Ⅲ Practical Application: GPIO Protection Using Clamper CircuitsA practical application of clamping diodes is found in GPIO (General Purpose Input/Output) pin protection circuits. This example demonstrates the use of dual-diode clampers in the Qualcomm MSM8909 platform to prevent electrostatic discharge (ESD) damage and electrical overstress (EOS).Circuit AnalysisFigure 7. MSM8909 GPIO Internal Protection CircuitCircuit Configuration:Clamping diode D1: Cathode connected to VDD (positive supply rail), anode connected to GPIO pinClamping diode D2: Anode connected to GND (ground), cathode connected to GPIO pinProtection Mechanism:When input voltage > VDD: D1 conducts (forward-biased), D2 is off (reverse-biased). The GPIO pin voltage is clamped to approximately VDD + 0.6V, with excess current shunted to the VDD rail.When input voltage < GND: D1 is off (reverse-biased), D2 conducts (forward-biased). The GPIO pin voltage is clamped to approximately GND - 0.6V, with excess current shunted to ground.Normal operation (GND < Vin < VDD): Both diodes remain off, allowing normal signal operation without interference.This dual-diode configuration effectively limits the input voltage to the safe operating range of [GND - 0.6V, VDD + 0.6V], protecting the GPIO pin from ESD events and voltage transients.Diagnostic Procedure: Testing GPIO Protection DiodesTo determine whether a GPIO pin has been damaged by ESD or EOS, follow this multimeter-based diagnostic procedure:Equipment Required:Digital multimeter with diode test functionAnti-static wrist strap (recommended)Circuit schematic or pinout diagramTest Procedure:Power Down: Ensure the device is completely powered off and disconnected from all power sources.Test Diode D2 (Lower Clamp to GND):Set multimeter to diode test modeConnect RED probe to motherboard GNDConnect BLACK probe to the GPIO pin under testExpected Result: Forward voltage drop of 0.4-0.7V (typically 0.6V for silicon diodes)Failure Indication: Reading significantly outside this range indicates D2 damage:Very low reading (< 0.2V): Diode is shortedOpen circuit (OL or > 2V): Diode is openTest Diode D1 (Upper Clamp to VDD):Reverse probe connections:Connect RED probe to the GPIO pin under testConnect BLACK probe to VDD rail (or appropriate power pin)Expected Result: Forward voltage drop of 0.4-0.7VFailure Indication: Similar interpretation as D2 testReverse Bias Test (Optional):Reverse the probe connections for each testExpected Result: Open circuit (OL) or very high resistanceFailure Indication: Low resistance in reverse bias indicates diode breakdownImportant Notes:Always discharge any residual capacitance before testingSome modern ICs may have additional protection elements that affect readingsCompare readings with a known-good board when possibleDocument all measurements for troubleshooting recordsIf protection diodes are damaged, the internal GPIO circuitry may also be compromisedFrequently Asked Questions about Clamper Circuits1. What is a clamper circuit and what are its types?A clamper circuit is an electronic circuit that shifts the DC level of an AC signal to a desired voltage level without altering the shape of the waveform. Since the DC level is shifted, a clamper circuit is also called a level shifter. Clamper circuits utilize energy storage elements, primarily capacitors. A basic clamper circuit consists of a capacitor, a diode, a resistor, and optionally a DC bias voltage source. The main types are: positive clampers (shift waveform upward), negative clampers (shift waveform downward), and each can be either biased (with reference voltage) or unbiased (simple configuration).2. How do clamper circuits work?A clamper circuit operates by using a capacitor to store charge during one half-cycle of the input signal and a diode to control the charging and discharging process. During the half-cycle when the diode conducts, the capacitor charges to approximately the peak voltage of the input signal. During the opposite half-cycle, the diode blocks, and the capacitor voltage adds to (or subtracts from) the input voltage, effectively shifting the entire waveform up or down. The RC time constant must be large enough (typically RC ≥ 10T) to maintain the capacitor charge between cycles, ensuring consistent clamping action.3. What is a diode clamper circuit?A diode clamper circuit is a specific implementation of a clamper that uses a diode as the switching element to control the charging of the capacitor. The circuit consists of a capacitor, a diode, and a resistor arranged to shift the waveform to a desired DC level. The diode's unidirectional current flow property ensures that the capacitor charges during one half-cycle and maintains its charge during the other half-cycle, creating the clamping effect. The diode's orientation determines whether the circuit functions as a positive or negative clamper.4. How many diodes are used in a clamper circuit?A basic clamper circuit requires a minimum of one diode, along with a capacitor and a resistor. However, protection circuits and bidirectional clampers may use two diodes connected in reverse parallel (anti-parallel) configuration to provide clamping in both positive and negative directions. Some advanced designs may incorporate additional diodes for improved performance, temperature compensation, or multiple voltage level clamping. An independent DC voltage source may also be added to create biased clamper circuits with adjustable reference levels.5. What is a clamping diode used for?Clamping diodes serve multiple purposes in electronic circuits: (1) Level Shifting: They shift AC signals to desired DC levels in signal processing applications. (2) Voltage Protection: They protect sensitive components from overvoltage conditions by limiting voltage excursions to safe levels (typically within ±0.6V of supply rails). (3) ESD Protection: In integrated circuits, clamping diodes protect GPIO pins and other I/O interfaces from electrostatic discharge damage. (4) Transient Suppression: They absorb voltage spikes and transients in power supply and signal lines. (5) Signal Restoration: In video and communication systems, they restore DC components that may be lost during AC coupling or transmission.6. What is the difference between a clipper and a clamper circuit?Clipper circuits cut off or limit portions of the input waveform that exceed certain voltage levels, fundamentally changing the waveform shape. Clamper circuits preserve the entire waveform shape but shift its DC level (vertical position on the voltage axis). Clippers are used for waveform shaping and overvoltage protection, while clampers are used for DC restoration and level shifting. Clippers typically use diodes with resistors, while clampers require capacitors in addition to diodes and resistors.7. Why is the RC time constant important in clamper circuits?The RC time constant (τ = R × C) determines how quickly the capacitor charges and discharges. For proper clamping action, the RC time constant must be much larger than the period of the input signal (typically RC ≥ 10T). This ensures that: (1) The capacitor charges quickly during the conducting half-cycle of the diode, (2) The capacitor maintains its charge during the non-conducting half-cycle with minimal voltage droop, and (3) The clamping level remains stable across multiple cycles. If the RC time constant is too small, the capacitor will discharge significantly between cycles, resulting in poor clamping performance and waveform distortion.ConclusionClamper circuits are essential components in modern electronics, providing DC level shifting and voltage protection across a wide range of applications. Understanding the operating principles of positive and negative clampers, both biased and unbiased configurations, enables engineers to design effective signal conditioning and protection circuits. The practical application in GPIO protection demonstrates the critical role of clamping diodes in safeguarding sensitive integrated circuits from ESD and overvoltage damage. Proper component selection, particularly regarding the RC time constant and diode characteristics, is crucial for optimal clamper circuit performance.Note: This article was originally published in 2020 and has been updated in 2025 to reflect current technology standards, correct technical inaccuracies, and include additional practical information about clamper circuit applications and diagnostics.

IntroductionFLASH is a type of non-volatile memory that retains data even when power is disconnected. Unlike RAM, which can rewrite data at the byte level, flash memory operates differently. A flash memory chip consists of an array of data storage cells organized into blocks, with each block containing multiple pages (typically 64 to 256 pages in modern devices, though older devices used 32 pages). A page is usually 2KB, 4KB, 8KB, or 16KB in modern NAND flash, though the original specification was 512 bytes plus spare area, as flash was initially developed as a disk replacement technology.What Is Flash Memory?Ⅰ Types of Flash MemoryFlash memory is widely used as a storage medium in digital cameras, smartphones, tablets, USB drives, SSDs, and various consumer electronics. Flash memory cards come in various form factors depending on manufacturers and applications, including USB flash drives, CompactFlash (CF card), MultiMediaCard (MMC card), Secure Digital (SD card, microSD), Memory Stick, and XD-Picture Card (XD card). Note that SmartMedia (SM card) and Microdrive have been discontinued. While these flash cards have different physical formats and specifications, their underlying technical principles remain similar.Flash memory includes two main architectural types: NOR Flash and NAND Flash. NOR Flash is a random access device with dedicated address and data lines (similar to SRAM), allowing byte-level read and write operations and direct access to any memory location, making it an excellent ROM alternative, such as in computer BIOS chips. NAND Flash, however, lacks dedicated address lines and cannot be directly addressed. It is controlled by sending commands and addresses through an I/O interface, meaning NAND Flash can only be accessed in pages, making it more suitable for sequential data storage.Ⅱ NAND Flash MemoryNAND Flash is extensively used in high-capacity storage devices such as memory cards, USB drives, SSDs, eMMC, and UFS storage. NAND Flash cells are categorized by the number of bits stored per cell: SLC (Single-Level Cell), MLC (Multi-Level Cell), TLC (Triple-Level Cell), and QLC (Quad-Level Cell). SLC stores 1 bit per cell, MLC stores 2 bits, TLC stores 3 bits, and QLC stores 4 bits per cell.As more bits are stored in a single cell, the read/write performance decreases, endurance diminishes, but cost per gigabyte is reduced, making higher-density options more economical for consumer applications.ItemsSLCMLCTLCQLCBits Per Cell1234P/E Cycles50,000-100,0003,000-10,0001,000-3,000100-1,000Read Time (μs)255075100Program Time (μs)200-300600-900900-13501350-2000Erase Time (ms)1.5-234.56-8SLC is primarily used in enterprise, industrial, and military applications due to its high-speed writing, low error rate, and exceptional durability.MLC is targeted at consumer and prosumer applications, offering twice the capacity of SLC at lower cost. It's suitable for USB drives, smartphones, digital cameras, and consumer-grade SSDs.TLC has become the mainstream choice for consumer SSDs and SD cards due to its balance of cost, capacity, and acceptable performance for everyday use.QLC, introduced more recently, offers even higher density and lower cost per gigabyte, making it increasingly popular in budget SSDs and high-capacity storage solutions, though with reduced endurance.As a practical solid-state storage medium, NAND Flash has unique physical characteristics requiring specialized management. Designers face several key challenges:1) Erase-before-write requirement: Data cannot be overwritten directly; blocks must be erased before new data can be written2) Wear mechanism: Limited program/erase (P/E) cycles impose durability constraints3) Read/write interference: Operations can cause data errors in adjacent cells4) Data retention: Charge leakage over time can cause data loss5) Bad block management: Both factory defects and runtime failures must be managedKey technologies addressing these challenges include:1) Cell type selection: Choosing appropriate NAND type (SLC/MLC/TLC/QLC) based on application requirements2) Wear leveling algorithms: Distributing write operations evenly across all blocks to maximize lifespan3) Bad block management: Identifying and mapping out defective blocks to ensure data integrity4) Error Correction Code (ECC): Detecting and correcting bit errors using advanced algorithms like BCH or LDPC5) Write amplification mitigation: Minimizing unnecessary write operations to extend device life6) Garbage collection: Consolidating valid data and reclaiming space from partially used blocksData is stored as electrical charge in Flash memory cells. The amount of stored charge depends on the voltage applied to the Control Gate, which controls whether charge is injected or removed from the floating gate.1) For programming (writing) NAND Flash, voltage is applied to the Control Gate to inject electrons into the floating gate. When charge exceeds the threshold voltage (Vth), the cell represents a logical 0.2) For erasing NAND Flash, electrons are removed from the floating gate. When charge falls below the threshold voltage (Vth), the cell represents a logical 1. Ⅲ NOR Flash MemoryNOR Flash, similar to conventional memory, supports random access, enabling XIP (eXecute In Place) functionality. This allows code execution directly from the flash without copying to RAM, making it ideal for boot code, BIOS/UEFI firmware, and embedded system applications requiring immediate code execution.NOR Flash is categorized into two types based on host interface: Parallel NOR Flash and Serial NOR Flash.Parallel NOR Flash connects directly to the host controller with its contents mapped into the CPU address space, eliminating the need to copy to RAM. Early BIOS implementations used the FWH (Firmware Hub) interface, a parallel connection that has been largely obsoleted due to pin count and speed limitations.Serial NOR Flash is more cost-effective than Parallel NOR Flash and typically connects to the host processor or Platform Controller Hub (PCH) via SPI (Serial Peripheral Interface), Quad-SPI (QSPI), or Octal-SPI interfaces. Modern implementations support higher speeds through multi-lane configurations.Today, virtually all UEFI/BIOS firmware, embedded systems, IoT devices, and many consumer electronics use NOR Flash. Typical capacities range from 1MB to 256MB, with 16MB-128MB being common for modern UEFI implementations. While more expensive per gigabyte than NAND, NOR Flash offers superior reliability and random access performance.NOR Flash has slower erase speeds and lower erase cycle counts compared to NAND, but these limitations rarely impact BIOS/firmware performance or cause device failures due to the infrequent update nature of firmware. Ⅳ NAND Flash vs NOR FlashCompared with NOR flash memory, NAND flash memory requires fewer transistors per cell to store the same amount of data, resulting in smaller die size and higher storage density. This architectural difference makes NAND significantly more cost-effective for high-capacity storage applications.In terms of read speed, NOR flash memory offers faster random access than NAND flash memory, with typical access times of 50-100ns compared to NAND's page-based access. However, NAND flash memory significantly outperforms NOR in sequential write and erase operations. NAND's block-based erase operation is simpler and faster, erasing entire blocks (typically 128KB-4MB) at once.NOR flash memory requires all bits to be set to 1 during erase operations before programming. While NOR flash memory provides faster random access and simpler byte-level operations, its lower storage density and higher cost make it more suitable for code storage and execution. NAND flash memory provides extremely high cell density (modern single chips can exceed 1TB capacity), making it ideal for mass data storage with fast write and erase speeds. Additionally, NAND flash operates on page-based read/write units (typically 4KB-16KB) and block-based erase units, making it functionally similar to traditional disk drives.NAND Flash is more susceptible to bit errors than NOR Flash, necessitating robust Error Detection and Correction (EDC/ECC) algorithms. Modern NAND implementations use advanced ECC schemes like BCH (Bose-Chaudhuri-Hocquenghem) or LDPC (Low-Density Parity-Check) codes. Additionally, NAND Flash develops bad blocks over its lifetime. File systems like FAT on SD cards experience frequent rewrites of the file allocation table, and the P/E cycle count per block is critical to NAND Flash longevity. Balancing erase cycles across all blocks and managing bad blocks requires specialized firmware-level functionality including bad block management, wear leveling, ECC, and garbage collection. This management layer is called the FTL (Flash Translation Layer). Based on FTL implementation location, Flash Memory is categorized as Raw Flash or Managed Flash.Raw Flash requires the host system to implement FTL functionality, giving designers complete control but requiring significant software development. Managed Flash (such as eMMC, UFS, SD cards) includes an integrated controller that handles FTL operations transparently, simplifying host system design at the cost of reduced low-level control.Ⅴ Universal Flash Storage Versions ComparisonStorage performance significantly impacts device responsiveness and user experience. Universal Flash Storage (UFS) has become the dominant standard for high-performance mobile and embedded storage, replacing the older eMMC standard. UFS provides a standardized flash storage specification optimized for smartphones, tablets, automotive systems, and other performance-critical applications. Version numbers indicate generational improvements, with higher versions offering substantially better performance, features, and efficiency.✔️Version Comparison (Main Parameters)UFS Version1.01.12.02.13.03.14.0Introduced2011-02-242012-06-252013-09-182016-04-042018-01-302020-01-302023-09-14Bandwidth per lane300 MB/s600 MB/s1450 MB/s (HS-G3)2900 MB/s (HS-G4)5800 MB/s (HS-G5)Max. number of lanes12Max. total bandwidth300 MB/s1200 MB/s2900 MB/s (HS-G3)5800 MB/s (HS-G4)11600 MB/s (HS-G5)M-PHY version1.03.04.15.0UniPro version1.41.61.82.0✔️UFS 2.1 vs UFS 2.2The primary enhancement in UFS 2.2 over UFS 2.1 is the Write Booster feature, which significantly improves write performance. Write Booster uses SLC (Single-Level Cell) cache to accelerate write operations, providing faster application launches, improved browser cache loading, reduced video encoding times, and enhanced overall system responsiveness. This feature is particularly beneficial for burst write scenarios common in mobile devices.As eMMC has been phased out from mainstream consumer devices and NAND flash prices have decreased, UFS adoption has accelerated. UFS 2.2 briefly served as a transitional standard before UFS 3.x became mainstream in flagship devices.✔️UFS 3.0 vs UFS 3.1UFS 3.1 introduces three significant enhancements over UFS 3.0:1) Write Booster (Enhanced)Write Booster in UFS 3.1 is an enhanced version that increases device write speed substantially. This feature can boost write speeds up to 700 MB/s, compared to UFS 3.0's typical sequential write performance of around 500 MB/s. The mechanism works similarly to SLC caching in SSDs: a portion of TLC/QLC storage is dynamically configured to operate in SLC mode, providing faster write performance. Data is initially written to this high-performance buffer, then migrated to standard storage during idle periods, freeing the cache for subsequent operations.2) Deep Sleep ModeDeep Sleep enables the flash memory to enter an ultra-low-power state during extended idle periods, significantly reducing standby power consumption. This feature helps extend battery life during device standby and contributes to overall device thermal management. Deep Sleep can reduce idle power consumption by up to 40% compared to standard sleep modes.3) Host Performance Booster (HPB)HPB addresses long-term performance degradation by improving random read performance. As devices are used over time, file system fragmentation and the need to frequently reload the Logical-to-Physical (L2P) mapping table can cause performance degradation. HPB leverages the host device's RAM to cache portions of the L2P mapping table, reducing latency for random read operations. This is particularly effective at maintaining consistent performance after extended use, preventing the "slowdown over time" phenomenon common in storage devices. HPB can improve random read IOPS by up to 70% in fragmented scenarios.✔️UFS 4.0 - The Latest GenerationReleased in September 2023, UFS 4.0 represents the latest advancement in mobile storage technology. Key improvements include:• Doubled bandwidth: Up to 11.6 GB/s (5800 MB/s per lane with dual-lane configuration) using HS-G5 gear• Improved power efficiency: Lower power consumption per bit transferred compared to UFS 3.1• Enhanced thermal management: Better heat dissipation characteristics for sustained performance• Advanced features: Builds upon Write Booster, Deep Sleep, and HPB with further optimizationsUFS 4.0 is designed for next-generation flagship smartphones, tablets, and high-performance mobile devices requiring extreme storage bandwidth for 8K video recording, advanced computational photography, and AI workloads. Frequently Asked Questions about Flash Memory1. What are the different types of flash memory?Flash memory comes in two fundamental architectural types: NOR and NAND. NOR flash offers random access and execute-in-place capabilities, making it ideal for code storage. NAND flash provides higher density and faster write speeds, making it suitable for data storage. Within NAND flash, there are further subdivisions based on bits per cell: SLC (1 bit), MLC (2 bits), TLC (3 bits), and QLC (4 bits), each offering different trade-offs between performance, endurance, and cost. 2. What are the characteristics of flash memory?Flash memory has several distinctive characteristics: it is significantly less expensive than EEPROM and doesn't require batteries for data retention unlike SRAM. It is non-volatile, meaning data persists without power. Flash offers fast read access times (microseconds), high resistance to physical shock compared to hard disk drives, low power consumption, and silent operation. However, it has limitations including finite write/erase cycles, block-level erase requirements, and potential for bit errors requiring ECC. 3. What is the purpose of flash memory?Flash memory serves as a non-volatile storage solution widely used in embedded systems, consumer electronics, and enterprise storage. It retains data without power, can be electrically erased and reprogrammed, and offers advantages over traditional magnetic storage including faster access times, lower power consumption, better durability, and compact form factors. Flash memory evolved from EEPROM technology and has become the dominant storage technology for mobile devices, SSDs, USB drives, memory cards, and embedded systems. 4. What is the difference between NAND flash and NOR flash?NOR flash provides faster random read access and supports execute-in-place (XIP), allowing direct code execution without copying to RAM, making it ideal for firmware and boot code. However, it's more expensive and has slower erase/write operations. NAND flash offers higher storage density, lower cost per gigabyte, and much faster sequential write and erase speeds, making it ideal for mass storage applications. NAND is accessed serially through a shared I/O interface, while NOR has parallel address and data buses allowing random access. NAND requires more complex error correction due to higher bit error rates. 5. What is the difference between UFS and eMMC?UFS (Universal Flash Storage) is the successor to eMMC (embedded MultiMediaCard) and offers several significant advantages: UFS supports full-duplex operation allowing simultaneous read and write operations, while eMMC is half-duplex. UFS uses a faster serial interface with higher bandwidth (up to 11.6 GB/s in UFS 4.0 vs. 400 MB/s in eMMC 5.1). UFS also features command queuing for better multitasking performance, lower latency, and improved power efficiency. These advantages make UFS the preferred choice for modern flagship smartphones and high-performance mobile devices. 6. How does wear leveling work in flash memory?Wear leveling is a technique used to extend flash memory lifespan by distributing write and erase cycles evenly across all memory blocks. Since flash memory has a limited number of program/erase cycles per block, repeatedly writing to the same blocks would cause premature failure. Wear leveling algorithms track the erase count of each block and preferentially use blocks with lower erase counts for new writes. This ensures all blocks wear out at approximately the same rate, maximizing the overall device lifespan. Modern flash controllers implement sophisticated wear leveling algorithms as part of the Flash Translation Layer (FTL). 7. What is 3D NAND technology?3D NAND (also called V-NAND) is a flash memory architecture that stacks memory cells vertically in multiple layers, rather than arranging them in a single planar layer. This technology allows for higher storage densities without requiring smaller manufacturing process nodes. Modern 3D NAND implementations can have over 200 layers, significantly increasing capacity while improving performance and endurance compared to planar NAND. 3D NAND also offers better power efficiency and can achieve higher performance due to reduced cell-to-cell interference. This technology has become the standard for modern SSDs and high-capacity storage devices.

IntroductionWith the improvement of living standards, all kinds of electrical equipment have gradually entered thousands of households. In many electrical appliances, air conditioning is also essential. However, many consumers are ignorant of the working principles of air conditioners and the principles of cooling and heating. In fact, for the operation of the air conditioner, the key to its operation is the air conditioner capacitor. Without this part, the air conditioner cannot operate normally. So what exactly is an air conditioner capacitor? What are the structural characteristics of this part?CatalogⅠ What is Air Conditioner CapacitorⅡ Types of Air Conditioner Capacitor  2.1 Electrolytic Capacitor    2.2 Safety Capacitor   2.3 Ceramic Capacitor   2.4 Capacitors for Starting and Running Air ConditionerⅢ Structure Characteristic of Air Conditioner CapacitorⅣ Working Principle of Air Conditioner CapacitorⅤ Main Reasons for the Failure of Air Conditioner Capacitor  5.1 Heat Exposure    5.2 Voltage Capacity    5.3 Shorter LifespanⅥ The Detection of Air Conditioner CapacitorⅦ Methods to Repair And Replace Air Conditioner CapacitorⅧ Frequently Asked Questions about Air Conditioner CapacitorⅠ What is Air Conditioner CapacitorThe so-called air conditioner capacitors are also called aluminum electrolytic capacitors. It is a capacitor made of an aluminum cylinder as the negative electrode, which is filled with liquid electrolyte, and inserted into a curved aluminum strip as the positive electrode. The core of the air conditioner capacitor is made by overlapping and winding anode aluminum foil, liner paper impregnated with electrolyte, cathode aluminum foil, and natural oxide film. After the core is immersed in the electrolyte, it is sealed with an aluminum shell and a plastic cover to form an air conditioner capacitor. Generally, there is a plastic sleeve outside the aluminum shell of the air conditioner capacitor.So-called air conditioner capacitiorsAlso, it's a little cylindrical container within your air conditioner that stores and distributes energy. When you turn on your air conditioner, it demands more power than your home's electrical system can provide—this is where the capacitor comes in. Moreover, the AC capacitor is a component within the outdoor condensing unit of an air conditioner or heat pump. It delivers power to the motor driving the air conditioning system. The capacitor delivers initial energy burst to turn the system on when it's time for a cooling cycle.) Ⅱ Types of Air Conditioner Capacitor2.1 Electrolytic Capacitor This capacitor for air conditioner has polarity and leads labeled with + or - marks. It is typically used to smoothen the DC voltage after it has been rectified by diodes. They aided in reducing the ripples in the DC supply. The smaller the ripple, the larger the capacitance of the capacitor employed. This use can be seen in a simple linear power supply with a step-down transformer.2.2 Safety CapacitorSafety capacitors are commonly used in the inverter control circuit of an air conditioner. They can be classified into X or Y types and used in the circuit's live parts always be careful when dealing with these capacitors as some charge on them may cause shock even when the power supply has been cut off.Safety Capacitor PictureGood design should have bleeding resistors to remove the charge from the device after the air conditioner has been switched off. Ensure proper certification marks such as VDE, UL and CE markings are present on the bodies of the capacitors before using them. Together with inductor coils, these capacitors are used to reduce the harmonics generated from the rapid switching of the AC power supply by the insulated gate bipolar transistors (IGBT).2.3 Ceramic Capacitor Ceramic capacitors are used as bypass capacitors to bypass the high-frequency content of a circuit. They could be placed parallel to the DC power intake of integrated circuits to bypass certain high frequencies noise in the circuit that may have an adverse effect on the sensitive circuitry. As the more transformerless power supply is becoming common today due to its better efficiency and smaller space, you will see many surface mount capacitors being used in multilayer printed circuit boards. These capacitors and inductor coils are used to reduce the harmonics, which are generated from the rapid switching of the AC power supply by the insulated gate bipolar transistors (IGBT).2.4 Capacitors for Starting and Running Air ConditionerThese capacitors are commonly used in single-phase electric motors. START capacitor is used to alter the phase difference between a capacitor-start motor's START and RUN windings. This difference resulted in the generation of a starting torque capable of starting the motor with a full load connected to it. Start and Running CapacitorThe RUN cap. is used to further adjust the phase difference between the two windings, resulting in even more beginning torque. The connections in the motor are identified by marks on the single-phase compressor. The designations are R (connected to the RUN winding), S (connected to the START winding), and C (connected to the CUT winding) (common of the two windings).Ⅲ Structure Characteristic of Air Conditioner Capacitor1) The working medium of the air conditioner capacitor is to form a very thin layer of aluminum oxide (Al2O3) on the surface of the aluminum foil through anodization. This oxide dielectric layer and the anode of the capacitor are combined into a complete system, and the two are interdependent. The electrodes and dielectrics of what we usually call capacitors are independent of each other. 2) The anode aluminum foil and cathode aluminum foil of air conditioner capacitors are usually corroded aluminum foil, and the actual surface area is much larger than its apparent surface area. It is one reason why air conditioner capacitors usually have large capacitance. Due to the use of aluminum foil with many fine etched holes, the liquid electrolyte is usually needed to more effectively use its actual electrode area.The Structure of  Airconditioner Capacitors  3) The negative foil acts as an electrical lead in the air conditioner capacitor. Because the electrolyte as the cathode of the air conditioner capacitor cannot be directly connected to the external circuit, an electrical path must be formed through another metal electrode and other parts of the circuit. 4) Since the dielectric oxide film of the air conditioner capacitor is obtained by anodic oxidation, and its thickness is proportional to the voltage applied by the anodic oxidation, in principle, the thickness of the dielectric layer of the air conditioner capacitor can be artificially and accurately controlled. It is precisely because of the structure characteristics and functions of the air conditioner capacitor that the air conditioner can operate normally. It should be noted that the capacitor should be checked for short circuit, open circuit and leakage before it is installed in the circuit, and its capacitance value should be checked. When installing, make it easy to see the capacitor type, capacity, withstand voltage and other symbols for verification. The above points are related introductions to the structure characteristics of air conditioner capacitors. In fact, for air conditioner capacitors, it is not just used in air-conditioning. But there are many applications, such as air conditioning inverters, color TVs, displays, LED lights, energy-saving lamps and so on. Relatively speaking, the scope of application of air conditioner capacitors is usually in the field of household appliances.Ⅳ Working Principle of Air Conditioner CapacitorThe capacitor is a key component to start the air conditioner motor. Most air conditioners on the market now use capacitors to start the air conditioner and take into account the operation. The damage of the capacitor will cause the compressor start current to rise too quickly, automatically turn on the protection mode to stop or fail to start the compressor, which will cause the air conditioner to fail to operate normally or automatically power off during the startup process. When the air conditioner is powered on, the capacitor acts as conduction to help the compressor start normally. The capacitor gathers and stores energy while your air conditioner is running; in other words, it functions similarly to a rechargeable battery. That way, when your air conditioner requires a large burst of energy, the capacitor can supply it and keep everything working smoothly. The compressor (or compressors, depending on your air conditioner) powers the air conditioner's compressor, blower motor, and fan motor, which all rely on the compressor to stay operating and cold air flowing through your home.Ⅴ Main Reasons for the Failure of Air Conditioner CapacitorA capacitor experiences significant strain over its lifetime and using an air conditioner more frequently than typical increases this strain. Most capacitors are designed to last approximately twenty years under ideal conditions, although ideal conditions are not usually met. There are three major causes of failure for most capacitors:This vedio shows that how to tell a AC Capacitor is bad !5.1 Heat ExposureHeat exposure is a term used to describe the condition of being exposed to heat.While air conditioners are designed to keep you cool in hot weather, the hotter the environment, the more likely your capacitor will fail. Overheating the machine might cause harm and limit its lifespan. Keeping your air conditioner covered and well ventilated is an important aspect of reducing the risks of high temperatures in Houston.5.2 Voltage CapacityThere are several air conditioner capacitors for various AC models, each with its voltage rating. The higher the voltage of a capacitor, the more expensive the part, so it may be tempting to replace it with a lower level capacitor. This, however, places a significantly greater demand on the capacitor, reducing its lifespan.5.3 Shorter Lifespan Again, most capacitors have a lifespan of roughly twenty years, but that also means they are only useful in certain situations. Older capacitors will be less capable, and higher-than-average AC consumption, as well as having a capacitor with malfunctioning parts, will limit its lifespan. One of the most serious issues with an AC capacitor failure is that it might cause harm to other components that it powers. Fans can wear out, and electric connections can be damaged—if you spot a problem with the capacitor, replace it as soon as possible to avoid extra maintenance needs and expenditures. Ⅵ The Detection of Air Conditioner CapacitorMethod 1: Use 220V alternating current to connect directly, you can connect one pole first, and touch the other capacitor pin with another power cord. If there is an obvious small spark when touched, you can be sure that the capacitor is charged, which means that the capacitor is not broken. Method 2: Pointer multimeter, you can also use the digital meter to measure capacitance. If you use a pointer multimeter, generally use the R × 1K gear, and connect the test leads to the two poles of the capacitor respectively. At this time, the pointer of the multimeter will swing and then slowly return to or near the zero position. Such a capacitor is good. The larger the capacity of the capacitor, the longer the charging time, and the slower the pointer swings in the 00 direction. If it is connected, the resistance value displayed by the pointer does not move, it is bad.The methods of dectecting a airconditioner capacitorMethod 3: Check with a digital multimeter. Set the digital multimeter to an appropriate resistance range. The red and black test leads respectively touch the two poles of the capacitor under test. At this time, the display value will gradually increase from 0 until the overflow symbol "1" is displayed. If 0 is always displayed, it means that the capacitor is short-circuited. If it always shows overflow, it may be an open circuit between the capacitors, or the selected resistance file is not suitable. The principle of selecting the resistance gear is: when the capacitor is large, the low resistance gear should be used; when the capacitor has a small capacity, the high resistance gear should be selected. Ⅶ Methods to Repair And Replace Air Conditioner CapacitorWhen you've established that your capacitor needs to be replaced, you have a few options. Because it is similar to a battery, the method is as simple as swapping it out for a new one. However, it is a bit more involved than simply removing the old capacitor and replacing it, so don't try it yourself if you aren't comfortable handling the parts.There are various tips on how to replace a capacitor on your own, however here are some fundamentals to remember:  Find the right replacement capacitor. The capacitor should have a voltage and capacitance level on it, and you need to match that in your replacement. Writing down that and the make and model of your air conditioner can help the type of capacitor you need. Power down your air conditioner before starting any fixes. It may sound like common sense, but it’s still vital. Working with high-electricity machinery can be dangerous without proper safety. Discharge the capacitor. Even with your air conditioner turned off, the capacitor still has a significant amount of energy stored inside (that’s it is a job, after all). You need to discharge that energy so as not to cause damage to yourself during handling or after disposal. Make sure to wear proper safety equipment as well.Take notes. Either draw a diagram of how your capacitor is connected or take several pictures to aid in the reconnection process.Be aware of capacitor differences.·B If you’ve selected the same type of capacitor as your old one, this won’t be as much of an issue. However, some capacitors have different labels for the connections you need, so be aware of where these need to reattach so that you don’t have additional troubles.Ⅷ Frequently Asked Questions about Air Conditioner Capacitor1. What does a capacitor do for an air conditioner?The main job of capacitors is to store electrons to provide start-up energy for your air conditioner, they build up a charge when electricity runs through them by swapping electrons between the two conductive plates inside. 2. How much does it cost to replace a capacitor on an air conditioner?The average HVAC capacitor cost is around $170. Prices generally range between $120 and $250, including professional installation. Branded units are more expensive, costing upwards of $400 or more. The price you pay depends on the brand, model, voltage and the labor required for installation. 3. How long does an AC capacitor last?The life expectancy of the air conditioner capacitor lies between 10-20 years. However, various factors, such as heat exposure, may tamper with their lifespan. If your capacitor is tiny or was built with the wrong parts, it may not live long. 4. Why is AC running but not cooling?Condenser Unit is BlockedIf your air conditioner is running, but not lowering temperatures inside, one issue could be a blocked or clogged condenser coil. When operating correctly, the condenser fan draws air into the outdoor unit through the condenser coil to pull heat energy out of your home. 5. Can I replace the AC capacitor myself?Yes, you can. It could be a capacitor, or it could be a compressor. Since capacitors are cheap, it may be worth a try to see for yourself if that's it, if not you will need a technician. There is really no “DIY” fix when it comes to repairing or replacing a capacitor. 6. How do I know what capacitor to get for my AC?Multiply the full load amps by 2,650. Divide this number by the supply voltage. The full load amps and the supply voltage can be found in the owner's manual. The resulting number is the MicroFarad of the capacitor you need. 7. Do air conditioner capacitors get weak?Power surges can cause a capacitor to fail, too.Obviously, a lightning strike from a summer thunderstorm can overload and burn out your HVAC's electrical system., Also weaker power surges can cause damage to capacitors over time. Those weaker surges can be caused by fluctuations in the electrical grid. 8. Should I turn off AC if it's not cooling?If your ac is still not cooling, there is one more thing you need to do. This is very important. TURN IT OFF and call your HVAC service provider to assist you. We always tell our customers to turn off an ac that is not cooling properly. 9. What does a bad capacitor look like?Well, bad caps typically have a domed or swollen top. Sometimes really bad caps can leak their electrolyte out of themselves too. Then you may see this brown crust around the capacitor, or perhaps on it. It often looks somewhat like a dried coffee stain.

IntroductionNowadays, more and more mobile phones support NFC function. Of course, many people don’t know what NFC really is. Near-Field Communication (NFC) is a short-range wireless technology. NFC has functions of mobile payment, data transmission, information browsing and access control. It provides a simple, touch-sensitive solution to exchange information, access content and services simply and intuitively. At the same time, NFC has the characteristics of low cost, easy to use and more intuitive, which makes it more potential in certain fields.What is NFC? How NFC Works? Applications of NFCCatalogIntroductionⅠ What is NFC On Phone?Ⅱ NFC Application ModeⅢ NFC Operational ModeⅣ NFC Uses On PhoneⅤ Which Phones Have NFC?Ⅰ What is NFC On Phone?In theory, NFC is a set of protocols for communication between two electronic devices about four inches at the most. So you device have to be very close to another NFC enabled device to transfer the data or do payment, in other words, long distance or non NFC devices will not be able to operate normally. NFC evolved from the integration of radio-frequency identification (RFID) and interconnection technology. It combines inductive card readers, inductive cards and point-to-point functions on a chip, which can identify and exchange data with compatible devices within a short distance exchange. NFC was originally a simple merger of RFID technology and network technology in the pass, and now has evolved into a short-range wireless communication technology. With the popularity of smart phones, it develops rapidly.Like RFID, NFC information is also transmitted through electromagnetic induction coupling in the wireless frequency part of the spectrum, but there is still a big difference between the two. First of all, NFC is a wireless connection technology that provides easy, safe, and rapid communication experience. Its transmission range is smaller than that of RFID, because RFID can support several meters or even tens of meters. What’s more, due to the unique signal attenuation technology adopted by NFC, NFC has the characteristics of short distance, high bandwidth, and low energy consumption.With NFC mobile phones, people can get the services and transactions at any place in any time. In short, through NFC-supported devices, people can complete payment or transfer data.Ⅱ NFC Application ModeNFC devices can be used as contactless smart cards, write/read terminals, and device-to-device data transmission paths. It has a wide range of applications, which can be divided into three basic types:Close→Finish. For applications such as access control or traffic/event ticket checking, users only need to bring the device storing the ticket or access code close to the reader. It can also be used for simple data capture applications, such as reading URLs from smart tags on posters.Close→Confirm. In applications such as mobile payment, the user must enter a password to confirm the transaction, or only accept the transaction.Close→Connect. By linking two NFC-enabled devices, you can perform point-to-point network data transmission, such as downloading music, exchanging images, or synchronizing address books.NFC devices may provide more than one function. Consumers can explore and understand the functions of the device and find out the potential functions and services of the NFC device. Ⅲ NFC Operational ModeNFC uses two-way recognition and connection. Its working modes include card emulation, P2P mode and reader/writer mode. Both NFC and Bluetooth are short-range communication technologies, and are integrated into mobile phones. NFC does not require complicated setup procedures, and it can also simplify Bluetooth connections. The advantage of NFC is that its setup procedure is shorter, but it cannot reach the low power compared with Bluetooth. The maximum data transfer capacity of NFC is 424 kbit/s, which is much smaller than Bluetooth V2.1 (2.1 Mbit/s). Although NFC is inferior to Bluetooth in transmission speed and distance, it does not require a power source. For mobile phones or portable electronic products, NFC is more convenient to use.NFC is superior to infrared(IR) transmission and Bluetooth. As a consumer-oriented transaction mechanism, NFC is faster, more reliable and much simpler than IR, which requires strict alignment to transmit data. Compared with Bluetooth, NFC is not suitable for long-distance data communication and. So NFC and Bluetooth complement each other and coexist. In fact, NFC protocol can be used to improve the Bluetooth pairing process between two devices.Ⅳ NFC Uses On PhoneAs a bus and subway card. we all know that most of our bills can be paid by mobile phones, but we often face a problem, that is, forgetting to bring the card or change. Now we have an NFC-enabled mobile phone to reduce embarrassing situations. Turn on the local subway and bus functions on the mobile phone, so that we can use the mobile phone to pay. To put it simply, the NFC function can turn your mobile phone into a bus card, you can also recharge the bus card online, and you can read the card data to check the balance, etc. At present, the most widely used field of NFC is also in bus/subway card.As a door-access card. It’s really troublesome to forget to bring the access card, but now we don’t have to worry, because the NFC function of the mobile phone can also be used directly as the access card to enter the door. We only need to click the virtual key in the mobile phone, and then place access card on the back of the mobile phone for data reading. After reading the relevant information, we can directly use the mobile phone’s NFC to act as the access card.Read the bank card information directly. For example, we usually need to check the consumption records of our bank card. We need to download the bank’s official software to be able to check or go to the bank. If the mobile phone has the NFC function, we can get the bank card information according to the relevant operation, like the bank card’s consumption records and balances, which is very convenient for us.Bluetooth speakers connected to NFC, there are many Bluetooth speakers on the market that are also equipped with NFC function. When we connect, we only need to use a mobile phone that supports NFC function to turn on the Bluetooth speaker, which is more than we need to set up Bluetooth before. Pairing connection is much more convenient.File transfer, although we can use the network to transfer files now, the speed is very fast, but if the mobile phone does not have a network, the NFC function is more important, only need to use the NFC function of the two mobile phones Open and paste together, we can transfer music, pictures or files, which is still very useful. Of course, now the same brand of mobile phones also have their own fast data transmission function, and no network is required.The above are some practical small functions that NFC can bring in mobile phones, which is still very practical for our lives. Of course, there are more other similar functions, we can stack them according to the actual situation.Ⅴ Which Phones Have NFC?The following smartphone models are all from the official website data, but there will be gaps in different regions, and all local models shall prevail.HuaweiSamsungMate X2, Mate XS, Mate X, Mate 40 RS, Mate 40 Pro+, Mate 40 Pro, Mate 40, Mate 40E, Mate 30, Mate 30 RS, Mate 30 Pro, Mate 30 Pro 5G, Mate 30 5G, Mate 20, Mate 20 RS, Mate 20 X 5G, Mate 20 X, Mate 20 Pro, Mate 10, Mate 10 Pro, Mate 9, Mate 9 Pro, Mate 8, Mate 7, Mate SW21, W20Z Fold2, Z FlipJ7 Pro, J7+, J7(2016), J5, J4, J3C9 Pro, C7 Pro, C7, C5 Pro, C5GRAND Prime, MEGA2, ALPHA G8508S, CORE Lite 4G, CORE AdvanceP40 Pro+, P40 Pro, P40, P30 Pro, P30, P20 Pro, P20, P10 Plus, P10Note20 Ultra, Note20, Note10+ 5G, Note10+, Note10, Note10 Lite, Note9, Note8, Note7, Note5, Note4, Note3nova 8 Pro, nova 8, nova 7 Pro, nova 7, nova 6, nova 5 Pro, nova 2sA90, A80, A71 5G, A71, A70, A60, A51, A50s, A31, A21s, A20, A9 Star Lite, A9, A8S, A8+, A8S21 Ultra, S21+, S21, S20 Ultra, S20+, S20, S10 5G, S10+, S9+, S9, S8+, S8 OnePlusMicrosoft LumiaOnePlus 8 Pro, OnePlus 7 Pro, OnePlus 7, OnePlus 6, OnePlus 5, OnePlus 3, OnePlus 1,OnePlus 8T, OnePlus 7T Pro, OnePlus 7T, OnePlus 6T, OnePlus 5T, OnePlus 3TLumia 950 XL, Lumia 950, Lumia 930, Lumia 925, Lumia 920, Lumia 650, Lumia 640 XL, Lumia 640 Apple IphoneSony Xperiaiphone 12 Pro, iphone 12, iphone 12 mini, iphone 11 Pro Max, iphone 11 Pro, iphone 11iphone XS Max, iphone XS, iphone XR, iphone Xiphone 8 Plus, iphone 8, iphone 7 Plus, iphone 7, iphone 6s Plus, iphone 6s, iphone 6 Plus, iphone 6iphone SE 2, iphone SEXperia 1, Xperia XZs, Xperia XZ2 Compact, Xperia XZ2 Premium, Xperia XZ2, Xperia XZ Premium, Xperia XZXperia XA2 Ultra, Xperia XA1 Ultra, Xperia XA1 Plus, Xperia XA1, Xperia X CompactLT29i, LT26i, MT27i, Xperia L1, Xperia E5 HTCLGHTC U UltraHTC Desire 21 Pro, HTC Desire 20+, HTC Desire 20 Pro, HTC Desire 19S, HTC Desire 19+, HTC Desire 12S, HTC Desire 626HTC U20 5G, HTC U12 Life, HTC U12+, HTC U11+, HTC U11, HTC U11 EYEsHTC 10 lifestyle, HTC 10New HTC One, HTC One E9+, HTC One M9, HTC One M8LG G7fitLG G7+ ThinQ, LG G7 ThinQ, LG G5, LG G4, LG G3, LG G2LG Q Stylus+, Q6+, Q6LG V40 ThinQ, LG V35 ThinQ, LG V30+, LG V30, LG V20, LG V10LG Stylus 3, LG Stylus 2+LG AKA RealmeZTERealme GT, Realme X50m, Realme X50 Pro, Realme X50, Realme X2 Pro, Realme X2ZTE Axon 7s, Axon 20 5G, Axon 11 5G, Axon 10 Pro 5G, Axon 10 Pro, ZTE T900, ZTE A602NubiaBlackBerryZ17 S, Z17, Z11, Z9 Max, Z9, Z7 Max, Z17 mini, Z5 mini, Z5S(LET)keyone, 9900, 9810(4G) Frequently Asked Questions about NFC Technology1. What is NFC technology?Near-Field Communication (NFC) is a set of communication protocols for communication between two electronic devices over a distance of 4 cm (11⁄2 in) or less. NFC offers a low-speed connection with simple setup that can be used to bootstrap more-capable wireless connections. It is a contact-less communication technology based on a radio frequency (RF) field. 2. How does near field communication NFC work?Near-field communication transmits data through electromagnetic radio fields to enable two devices to communicate with each other. To work, both devices must contain NFC chips, as transactions take place within a very short distance. 3. Do all mobile phones have NFC?All the latest Android smartphones can scan NFC without an app but there are a few older models that do not support NFC. 4. Is RFID same as NFC?The short answer: RFID stands for Radio Frequency Identification, a one-way communication method at varying distances. NFC, or Near Field Communication, is a version that allows for two-way communication. NFC is not totally contactless, typically requiring devices to be within a few inches of each other. 5. What is NFC vs Bluetooth?NFC is great for transferring small amounts of data over a very short distance and is used mostly for wireless payments and access cards. Bluetooth allows for a more extended range of connectivity and devices such as cellphones, speakers, and headphones commonly use it.

IntroductionLC circuit, also called passive filtering circuit, is commonly used for harmonic compensation, which does not require additional power supply. It is generally composed of capacitors, inductors and resistors. This kind of filtering circuit is easy to design, but its pass-band magnification and cut-off frequency vary with the load, which is not suitable for occasions with high signal processing requirements. Passive filtering circuits are usually used in power circuits, like DC power rectification, or large current loads.LC (Inductor-Capacitor) CircuitsCatalogIntroductionⅠ LC Circuit TypesⅡ LC Circuit CharacteristicsⅢ LC Circuit Working FeaturesⅣ LC Circuit FunctionsⅤ LC Circuit CalculationⅠ LC Circuit TypesCommonly used filter circuits include passive filter and active filter. If the circuit are only composed of passive components (resistors, capacitors, inductors), it is called a passive filter circuit. The main forms of passive filtering are capacitive filtering, inductive filtering and compound filtering (including inverted L-type, LC-type , LC-π type and RC-π type, etc.). The filter circuit is not only composed of passive components, but also composed of active components (bipolar tubes, unipolar tubes, integrated operational amplifiers), which is called an active filter circuit, and its main form is active RC(resistor-capacitor) circuit.The LC circuit has advantages of simple structure, high reliability, and wide range of applications. Its main feature is that the resistance of the inductor is small, and the DC loss is small. What’s more, the inductance in LC circuit to alternating current is large, so that the filtering effect is good.LC circuits are divided into LC low-pass filters, LC band-pass filters, high-pass filters, LC all-pass filters, and LC band-stop filters according to their functions. According to tuning, they are further divided into single-tuned filters, double-tuned filters and three-tuned filters and so on. The LC filter design process mainly considers its resonant frequency, capacitor withstand voltage, and inductor withstand current. In addition, it is necessary to pay attention to that passive LC circuits are not easy to integrate.  Ⅱ LC Circuit CharacteristicsThe LC circuit is generally formed by a proper combination of inductors, capacitors and resistors, and parallel with the harmonic source. It not only for filtering, but also takes into account the role of compensation.Figure 1. LC Circuit TypesThe following are the characteristics of several LC circuits:1) The load impedance of the L-type filter is high, and the source impedance is low.2) The load impedance of the inverted L filter is low, and the source impedance is high.3) The load impedance of the T-type filter is low, and the source impedance is low.4) The load impedance of the Π filter is high, and the source impedance is high.In actual use, these features are generally followed. In practice, impedance is difficult to estimate, especially in high frequency bands. Due to parasitic parameters, the circuit impedance changes greatly, and the circuit impedance is also related to the working state of the circuit, so the debugging shall prevail in practice. Ⅲ LC Circuit Working FeaturesAccording to the different impedance of reactive components to AC and DC, the basic form of the LC circuit composed of capacitor C and inductance L is shown in the figure. Because the capacitor C is open to DC and has a small impedance to AC, C is connected in parallel at both ends of the load, while the inductor L has a small impedance to DC and a large impedance to AC, so L should be connected in series with the load.In electronic circuits, the inductor coil acts on the finite current of the alternating current. From the inductance formula XL=2πfL, it can be known that the larger the inductance L, the higher the frequency f, and the larger the inductive reactance. We already know that capacitors have the ability to "block DC and pass AC", while inductors have the function of "pass DC, block AC, pass low frequencies, and block high frequencies". If the direct current accompanied by many interference signals is passed through the LC filter circuit, most of the AC interference signals will be prevented by the inductance from being absorbed and turned into magnetic induction and thermal energy, and most of the rest will be bypassed to the ground by the capacitor, which can suppress the interference. So a relatively pure DC current at the output is getting.The inductance of the power supply on PCB is generally made of a very thick enameled wire wrapped around a round magnetic core coated with various colors. In addition, there are usually several tall filter aluminum electrolytic capacitors nearby, which is a classic LC filter circuit. In addition, PCB also uses a large number of snake-type lines and chip tantalum capacitors to form an LC circuit. Few people notice, when design LC circuit, the snake line folds back and forth on the circuit board, which can also be regarded as a small inductance.In short, the principle of the LC filter circuit is actually a combination of the basic characteristics of the L and C components. Because the capacitive reactance of the capacitor xc=2nfc will decrease as the signal frequency increases, and the inductance of the inductor xl=2f will increase as the signal frequency increases. If the capacitors and inductors are connected in series, parallel or mixed together, the impedance of their combination will also vary greatly depending on the frequency of the signal. This shows that different filter circuits will present a small or large reactance to a certain frequency signal, so that it can pass or block the frequency signal. Thereby filter circuit plays a role in selecting a certain frequency signal and filtering out a certain frequency signal.Figure 2. LC Resonating CircuitsⅣ LC Circuit Functions1) LC circuit can be used as a filter circuit used in some power supplies. If the DC power with many interference signals is passed through the LC filter circuit, most of the AC interference signals will be blocked by the inductance and become magnetic induction and thermal energy. Most of them are bypassed to ground by capacitors, which can suppress the effect of interference signals and obtain relatively pure DC current output.2) Have oscillation effect, or sometimes generate a clock signal for the single-chip microcomputer (some have an external clock signal). 3) It can also be used as a frequency selection circuit, or a transmitting oscillation circuit (but it must be a circuit that can send and receive signals), and it also serves for the generation of input signals from other circuits.4) Since the output voltage of the rectifier circuit is not all pure DC, the output of the rectifier circuit observed from an oscilloscope is very different from the DC, and the waveform contains a large pulsating component, which is called ripple. In order to obtain the ideal DC voltage, it is necessary to use an LC circuit composed of reactive components (such as capacitors and inductors) with energy storage function to filter out the pulsating elements of output voltage.Ⅴ LC Circuit Calculation1) The voltage of the RC tank capacitor is:Voltage=U*exp(-t/rc)U represents the initial value of the voltage, rc represents the resistance and capacitance, t is the elapsed time, and exp (-t/rc) represents the -t/rc power of e.Time constant τ=rcNamely the product of capacitance and resistance, voltage = U*exp(-t/τ) after introducing the time constantTherefore, the voltage change with zero input response is an exponential decay process, theoretically infinite time, but generally it is considered that the decay is over after 3 to 5 time constants.Therefore, the discharge time depends on the time constant τ=rc2) For the LC oscillating circuit, it is related to the product of the LC circuit.Specifically, for the general LRC loop,R>2*sqr (L/R)R=2*sqr(L/R)R>2*sqr (L/R)sqr (X) represents the root sign (X)Divided into three situations, roughly speaking, the discharge time depends on the value of R, L, C in the circuit, U is not equal to 0 and I = 0, the capacitor discharges through L, RTwo eigenvalues can be obtained by solving second-order partial differential equations such as:p1=-(R/2L)+spr[(R/2L)*(R/2L)-1/LC]p1=-(R/2L)-spr[(R/2L)*(R/2L)-1/LC]Capacitor voltage=[U/(p2-p1)]*[p2exp(p1*t)-p1exp(p2*t)]Based on this, the relationship between capacitor discharge time and LRC can be analyzed. Frequently Asked Questions about LC Circuit1. What is meant by LC circuit?An LC circuit is a circuit that uses the elements inductor (L) and capacitor ( C). This circuit is also referred as resonating circuit, tank circuit, or tuned circuit. 2. What does an LC circuit do?LC circuits are used either for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal; this function is called a bandpass filter. 3. Where are LC circuits used?The LC circuit is used to select or generate a specific frequency signal. The application of LC circuits is reflected in many electronic devices, especially radio devices, such as transmitters, radio receivers and television receivers, amplifiers, oscillators, filters, tuners and frequency mixers. 4. What are the properties of LC circuit?An LC circuit is a closed loop with just two elements: a capacitor and an inductor. It has a resonance property like mechanical systems such as a pendulum or a mass on a spring: there is a special frequency that it likes to oscillate at, and therefore responds strongly to. 5. What is LC in LC oscillation?LC oscillations- The electric current and the charge on the capacitor in the circuit undergo electrical LC oscillations when a charged capacitor is connected to an inductor. The electrical energy stored in the capacitor is its initial charge which is named as q_m.

IntroductionInductor is a passive component that used extensively with capacitors and resistors to create filters for analog circuits and in signal processing. Also it is an energy storage device in many switched-mode power supplies. As a major value of inductor, inductance is the ratio of wire current and the magnetic flux which is created by the flow of electrical current in the magnetic field. When a DC current passes through the inductor, there are only fixed magnetic lines around it, which do not change with time. However, when an alternating current is passed through the coil, the magnetic lines around inductor that will change with time.Inductors and Inductance DefinitionCatalogIntroductionⅠ Inductor Working PrincipleⅡ What Does Inductor Do?Ⅲ Inductor Main ParametersⅣ Inductor ClassificationⅤ Chip Inductor5.1 Purpose of a Chip Inductor5.2 Chip Inductor Classification5.3 Three Methods for Reading Chip InductorsⅠ Inductor Working PrincipleWhen ac current is applied to an inductor coil, its own current changes, making its own magnetic flux to change, and then causing induced electromotive force. This phenomenon is called self-inductance. The direction of self-induced current always be affected. When the alternating current increases, the direction of self-inductance current is opposite to that of AC current. When the AC current is weaken, the direction of self-inductance current is the same as that of alternating current, which has blocking effect.1) Self-inductionWhen current flows through the coil, a magnetic field is generated around the coil. When the current in the coil changes, the surrounding magnetic field also changes accordingly. This changing magnetic field can cause the coil itself to generate induced electromotive force (EMF is used to represent the terminal voltage of the ideal power supply for active components).2) Mutual InductanceWhen two inductor coils are close to each other, the change of the magnetic field of one coil will affect the other one, and this effect is mutual inductance. The magnitude of the it depends on the degree of coupling between the self-inductance and the two coils. The components made by this principle are called mutual inductors.Ⅱ What Does Inductor Do?The inductor mainly plays the role of filtering, oscillating, delaying, tuning and frequency selection in the circuit, as well as filtering signal, filtering noise, stabilizing current and suppressing electromagnetic wave interference. The most common role of inductance in a circuit is to form an LC filter circuit together with a capacitor. Capacitors have the characteristic of "block DC and pass AC", while inductors have the function of "pass DC and block AC". It can be made into low-frequency and high-frequency choke coils by making use of its properties. Common filter inductors are for this purpose.➡️Pass DC: It means that in a direct current circuit, the inductor acts as a wire and has no effect.➡️Block AC: In an AC circuit, the inductor will have impedance, that is, XL. The current in the entire circuit will become smaller, which has a certain blocking effect on AC. The self-induced electromotive force is always opposed to the current change in the coil. Mainly can be divided into high-frequency choke coil and low-frequency choke coil.➡️Inductor has the function of generating self-induced EMF, which is also called energy storage function. Like a capacitor, it is also an important energy storage component, which is widely used in switching power supplies. In addition, the phase relationship between the voltage across the inductor and the current: the voltage leads the current by 90 degrees, which is just the opposite of the capacitor. Using this characteristic, inductors and capacitors form LC series and parallel circuits, which can be used for frequency selection. In reality, they have been widely used in circuits, especially in radio circuits.If the direct current accompanied by many interference signals is passed through the LC filter circuit, then the AC interference signal will be consumed by the inductance into heat. When the pure DC current passes through the inductor, the AC interference signal in it will also become magnetic induction and heat energy, the higher frequency is most likely to be blocked by the inductor, which used to suppress the higher frequency interference signal.➡️Tuning and Frequency SelectionThe inductance coil and the capacitor are connected in parallel to form an LC tuning circuit. That is, the natural oscillation frequency f0 of the circuit is equal to the frequency f of the non-AC signal, and the inductance and capacitive reactance of the loop are also equal, so the electromagnetic energy oscillates between the inductor and the capacitor. This is the resonance phenomenon of the LC loop. During resonance, since the inductance and capacitive reactance of the circuit are equal and opposite, the inductance of the total current of the loop is the smallest and the current is the largest (referring to the AC signal of f=f0), so the LC resonance circuit has the function of selecting the frequency, therefore an AC signal of a certain frequency is selected.➡️ChokeIt is used to block low-frequency alternating current, and pulsating direct current flows to pure direct-current in circuits. Go further, it is commonly used in the middle of two filter capacitors at the output of a rectifier circuit. The choke and capacitor form a filter circuit. In the high-frequency circuit: to prevent the high-frequency current from flowing to the low-frequency end, which is commonly as the high-frequency choke of old regenerative radio.➡️FilterIt also prevents the rectified pulsating DC current from flowing to the pure DC circuit. The choke (to simplify the circuit and reduce the cost, replace the choke with a pure resistance) and two capacitors (electrolytic capacitors) form a filter circuit. The use of capacitor charging and discharging and AC choke coil to block the alternating current to smooth direct current and obtain the pure direct current.➡️OscillationWe often say that rectification is to transform AC into DC, so oscillation is the reverse process of it. We call the circuit that completes this process an "oscillator." Oscillator waveform: there are sine wave, sawtooth wave, trapezoidal wave, square wave, rectangular wave, spike wave. The frequency ranges from a few Hz to tens of GHz. It is widely used in the field of wired power and radio.Ⅲ Inductor Main ParametersThe main parameters of inductor include inductance, allowable deviation, quality factor, distributed capacitance and rated current.1) InductanceInductance is also called self-inductance, which is a physical quantity that represents the self-inductance of an inductor. The size of the inductance mainly depends on the number of turns  of the coil, the winding method, the core and its material, etc. Generally, the more coil turns and the denser the coils, the greater the inductance. A coil with a magnetic core has a larger inductance than a coil without a magnetic core. What’s more, a coil with a larger magnetic core has a larger inductance.The basic unit of inductance is Henry, represented by the letter "H". Commonly used units are millihenry (mH) and microhenry (μH). The relationship between them is:1H=1000mH1mH=1000μH2) Allowable DeviationThe allowable deviation refers to the allowable error value between the nominal inductance and the actual inductance.Generally, inductors used in circuits such as oscillation or filtering require high accuracy, with an allowable deviation of ±0.2%~±0.5%; while the accuracy requirements of coils used for coupling and high-frequency blocking are not high; the allowable deviation is ±10 %~15%.3) Quality FactorQuality factor, also called Q value, is the main parameter to measure the quality of an inductor. It refers to the ratio of the inductance presented by the inductor to its equivalent loss resistance when it works under a certain frequency of AC voltage. The higher the Q value of an inductor, the smaller its loss and the higher its efficiency.The Q factor is related to the DC resistance of the coil wire, the dielectric loss of the coil frame, and the loss caused by the core and shield.4) Distributed CapacitanceDistributed capacitance refers to the capacitance that exists between the turns of the coil, the coil and the magnetic core, the coil and the ground, and the coil and the metal. The smaller the distributed capacitance of the inductor, the better its stability. Distributed capacitance can make the equivalent energy dissipation resistance larger. To reduce it, silk-covered wire or multi-strand enameled wire is commonly used, and sometimes honeycomb winding method is also used.5) Rated Current The rated current refers to the maximum current value that the inductor can withstand under the allowable working environment. If the operating current exceeds the rated current, the inductor will change its performance parameters due to heat, and even burn out due to overcurrent.Ⅳ Inductor ClassificationAccording to the form of inductor: fixed inductance, variable inductance.According to the nature of the magnetic conductor: air core coil, ferrite coil, iron core coil, copper core coil.According to work nature: antenna coil, oscillating coil, choke coil, trap coil, deflection coil.According to winding structure: single-layer coil, multi-layer coil, honeycomb coil.According to working frequency: high frequency coil, low frequency coil.According to structural characteristics: magnetic core coil, variable inductance coil, color code inductor coil, non-magnetic core coil, etc. Ⅴ Chip Inductor5.1 Purpose of a Chip InductorChip inductors are electromagnetic induction components wound with insulated wires. It is a commonly used electronic component. The function of the chip inductor: it is simple to say that it can isolate and filter the AC signal or form a resonant circuit with capacitors, resistors, etc. The inductor coil and capacitor in parallel can form an LC tuning circuit. Any current flowing through the chip inductor will generate a magnetic field, and its magnetic flux will act on the circuit.When the current passing through the chip inductor changes, the DC voltage potential generated in the chip inductor will prevent the current from changing. When the current passing through the inductor coil increases, and the current passing through the inductor coil decreases, the self-induced electromotive force is in the same direction as the current, which prevent the current from decreasing and release the stored energy at the same time. The direction of flow is opposite to prevent the increase of current, and at the same time, part of the electric energy is converted into magnetic field and stored in the inductor. Therefore, with inductor filtering, not only the pulsation of load current and voltage is reduced, the waveform becomes smooth, and the rectifier diode is turned on.The role of shielded chip inductors is different from that of the general one. The general chip inductors are not shielded in the circuit to achieve the desired effect. The shielded current instability of this kind inductor in some circuits plays a good blocking role. A metal shield surrounds the positively charged conductor, and the inside of the shield will induce the same amount of negative charge as the charged conductor. A positive charge equal to that of a charged conductor appears on the outside. If the metal shield is grounded, the positive charge on the outside will flow into the ground, and there will be no electric field on the outside, that is, the electric field of the positive conductor is shielded.The shielding inductance also plays a role of coupling in the circuit. In order to reduce the coupling interference voltage of the alternating electric field to the sensitive circuit, the inductance can be set with a metal shield with good conductivity between the interference source and the sensitive circuit, in addition, the metal shield is grounded. The coupling interference voltage to the sensitive circuit depends on the product of the alternating electric field voltage, the coupling capacitance and the ground resistance of the metal shield. As long as the metal shield is well grounded, the coupling interference voltage can be reduced. The electric field shielding is mainly based on reflection, so the thickness of the shielding body does not need to be too large, and the structural strength is the main consideration.5.2 Chip Inductor Classification1) Winding TypeIt is characterized by a wide range of inductance (mH～H), high inductance accuracy, low loss (that is, large Q), large allowable current, strong manufacturing process inheritance, simplicity, and low cost, and the shortcoming is size. For example, the ceramic core winding type chip inductor can maintain a stable inductance and a fairly high Q value at such a high frequency, so it occupies a place in the high-frequency circuit.NL series inductors are wire-wound type, 0.01~100uH, accuracy 5%, high Q value, which can meet general needs. NLC type is suitable for power circuit, rated current up to 300mA.NLV type is high Q value, environmentally friendly (reconstituted plastic), and can be interchanged with NL.NLFC has a magnetic screen and is suitable for power cords.2) Layer TypeIt has good magnetic shielding, high sintering density and good mechanical strength. The disadvantages of it are low pass rate, high cost, small inductance, and low Q value.Compared with wire wound chip inductors, it has many advantages: Small size is helpful to the miniaturization of the circuit.Closed magnetic circuit will not interfere with surrounding components, and will not be interfered by neighboring components, which is beneficial to high-density installation.Integrated structure, high reliability; good heat resistance and solderability.Regular shape is suitable for automatic surface mounting production.MLK type inductor has the characteristics of small size, good solderability, magnetic screen, high-density design, monolithic structure, and high reliability.MLG type has a small inductance and uses high-frequency ceramics, which is suitable for high-frequency circuits.MLK type working frequency is 12GHz, with high Q and low inductance (1n~22nH).3) Film TypeIt has the characteristics of maintaining high Q, high precision, high stability and small size in the microwave frequency band. The internal electrodes are concentrated on the same layer, and the magnetic field distribution is concentrated, which can ensure that the device parameters after mounting do not change much, and show good frequency characteristics above 100MHz.4) Weaving TypeIts characteristic is that the inductance per unit volume at 1MHz is larger than other chip inductors, small in size, and easy to install on the substrate. It is usually used as a miniature magnetic component for power processing.In actual applications, the inductor should be selected according to the situation, circuit requirement, and the material cost.5.3 Three Methods for Reading Chip Inductors1) Digital Position Identification (generally rectangular chip resistors use this nominal method)This method is to use three digits on the resistor to indicate its resistance. Its first and second digits are significant digits, and the third digit represents the number of "0"s added after the significant digits, no letters will appear in this place.For example: "472'" means "4720Ω"; "151" means "1510Ω". If it is a decimal, use "R" to mean "decimal point". It occupies one significant digit, and the remaining two are significant digits.For example: "2R4" means "2.4Ω"; "R15" means "0.15Ω".2) Resistor Color Code (generally cylindrical fixed resistors use this nominal method)Chip resistors are the same as general resistors. Most of them use four rings (sometimes three rings) to indicate their resistance. The first ring and the second ring are significant numbers, and the third ring is the magnification. For example: "brown, green and black" means "15Ω"; "blue, gray, orange and silver" means "68kΩ", the error is ±10%.3) E96 Number Mixes with LetterThis method also uses three digits to indicate the resistance value, that is, "two digits plus one letter". Two digits represent the E96 series resistance. Its third digit is the magnification expressed by the letter code. For example: "51D" means "332×103; 332kΩ"; "249Y" means "249×10-2; 2.49". Frequently Asked Questions about Inductor Uses1. What is inductor and its function?An inductor is arguably the simplest of all electronic components. It's a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. Typically, an inductor will consist of an insulated wire that's wound into a coil, much like a resistor. 2. What is the basic principle of inductor?An inductor is a passive electronic component which is capable of storing electrical energy in the form of magnetic energy. Basically, it uses a conductor that is wound into a coil, and when electricity flows into the coil from the left to the right, this will generate a magnetic field in the clockwise direction. 3. What is the function of inductor in AC circuit?Inductors store their energy in the form of a magnetic field that is created when a voltage is applied across the terminals of an inductor. The growth of the current flowing through the inductor is not instant but is determined by the inductors own self-induced or back emf value. 4. Does an inductor block AC?We know that inductor has inductive reactance property by which it opposes the flow of current through it. The equation of inductive reactance is, ... For this reason, an inductor can totally block the very high-frequency AC. 5. Why AC is blocked by inductor?Since inductor behaves like a resistor, DC flows through an inductor. The AC flowing through L produces timevarying magnetic field which in turn induces self- induced emf (back emf). ... For an ideal inductor of zero ohmic resistance, the back emf is equal and opposite to the applied emf.