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Catalog Introduction How does an LDR work? How to setup ADC in STM32 Introduction The majority of streetlights and outdoor lights are typically operated manually. To manually turn on and off lights is not only risky, but it also wastes energy well as the timing of turning on and off is not optimized. Therefore, an optimized, efficient, and automatic light system is needed to efficiently control light brightness and turn on and off them automatically. In this article, a brief introduction to automatic control of light brightness is given as well as its practical implementation using an STM32 microcontroller and a cheap LDR sensor shown in Figure 1 is demonstrated. Figure 1 LDR breakout board In an automatic light control system, a light detection system is employed that senses the light intensity. If the application requires only to turn on and off a light system, then a threshold value of light intensity is set below which the light will turn on, and above it, the light will turn off. However, if the application is to control the light brightness based on the light intensity in the environment, then a PWM-controlled voltage is provided to the automatic light system. For light detection, a Light Dependent Resistor commonly known as LDR is used. LDR is a sensor whose resistance varies with the intensity of light. This property of an LDR can be used to sense darkness and brightness. Thus, it can be used to automatically control the turn on and off as well as the intensity of the light system. A typical LDR has a maximum resistance value in mega ohms and a minimum resistance value in several kilo ohms. Materials 1STM32 F401/F1032LDR sensor3Potentiometer4LED How does an LDR work? So, how exactly does an LDR operate? LDR works on the principle of photoconductivity. It is an optical phenomenon in which material conductivity increases when light falls upon it. When light or photon strikes the material, the electrons in the semiconductor material's valence band are stimulated to the conduction band. The incident photons must have energy larger than the bandgap of the semiconductor material to cause the electrons to move from the valence band to the conduction band. Hence as light intensity increases more and more electrons are excited to the conduction band which produces a large number of charge carriers. This means that more current will flow in the circuit, and as a result, the resistance will decrease. LDR resistance that changes with the intensity of light cannot be read in a microcontroller. To make it readable in a microcontroller the resistance is represented in terms of voltage. For this purpose, a circuit needs to be designed. Many circuits can be used for LDR. These can be based upon MOSFET, BJET, or an amplifier. However, the most commonly used circuit for LDR to convert its resistance into voltage is the voltage divider circuit. In this circuit, two resistors are installed in series. One side is attached to the positive terminal of the battery while the other is attached to the ground. The schematic of the voltage divider is shown in Figure 2. The output of the voltage divider can be fed to another circuit for other purposes such as a comparator i.e LM393. Usually, a comparator is used in on-off operations where the lights are needed to be turned on and off when a threshold value of light intensity is absorbed by the LDR. A typical circuit for the LM393 comparator is shown below. Figure 2 LM393 comparator usage with LDR The calculation for the voltage divider circuit is pretty easy. Referring to Figure 2, the following equation can be used to measure the output voltage.   In this equation, it is assumed that there is no load on the output voltage because that load can affect the output voltage. The output of the circuit is shown in Figure 2 where the change in resistance changes the voltage at the IN1+ pin of the comparator. As we know the voltage changes with the intensity of light. The circuit gives maximum voltage in complete darkness while minimum voltage when placed in bright light. The ADC of the STM32 controller can be used to sense the change in the voltage while the results obtained via ADC can be used to generate PWM. It is the PWM that generates average voltage and hence controls the intensity of light. In this article, both the manual and automatic light intensity control is demonstrated using an LED light. The program and procedure for automatic and manual light brightness control is same, the only difference is that in automatic light brightness control and LDR is used while in manual mode simple potentiometer is used. How to setup ADC in STM32 In STM32, ADC can be configured in three different ways. 1) Polling 2) Interrupt 3) DMA. Polling: In the polling method when ADC conversion starts the CPU operation halts. It is only after the conversion is completed, the CPU resumes working. Interrupt: The second method is by using the interrupt service routine. When ADC conversion competes, it generates an interrupt during which required functions are executed which in our case is to update the PWM value. DMA: The third method is to use direct memory access (DMA). In this method, the ADC directly transfers the data to memory bypassing the CPU altogether. This is the most efficient method of all as it does not involve CPU in the ADC operations and keeps it available for other tasks. In this experiment, we will be using interrupt methods which are both simple and efficient. Required hardware STM32 F401/F103LDR sensor (breakout board will be better)PotentiometerLED Let's build the program step by step Open STM32CubeIDE and start a new projectSelect an MCU which in our case is STM32F401CDGo to SYS -> Debug and select Serial Wire. Select SystTick in TimeBase Source. Go to RCC-> High Speed Clock and select Crystal/Ceramic Resonator.   Configure ADC1. Select IN1 and set it to be triggered by software. From the NVIC controller tab check the global interrupt box. Configure Timer 1 in PWM mode with output on CH1. Set the counter period register value to 839 and Prescaler register value to 100. This will ensure 1000 Hz frequency at the output.  The following formula can be used to set PWM frequency Setting Prescaler value to 99 while the required frequency is 1000 Hz, the ARR value can be calculated as 839.     Finally set the clock frequency to 84 MHz and select HSE as the clock source. And generate the code. The final code is given below #include "main.h"ADC_HandleTypeDef hadc1;TIM_HandleTypeDef htim1;void SystemClock_Config(void);static void MX_GPIO_Init(void);static void MX_ADC1_Init(void);static void MX_TIM1_Init(void);uint16_t AD_Data = 0; uint16_t minimumADC = 1000; uint16_t maximumADC = 3000;int main(void){  HAL_Init()  SystemClock_Config();  MX_GPIO_Init();  MX_ADC1_Init();  MX_TIM1_Init();  HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);  while (1)  {  HAL_ADC_Start_IT(&hadc1);  TIM1->CCR1 = ((AD_Data-minimumADC)*840)/maximumADC;  }}void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc){    AD_Data = HAL_ADC_GetValue(&hadc1);} Figure 3 Duty Cycle in Bright Light Figure 4 Duty Cycle in Low Light   Resources Automatics Light.zip

IntroductionAn analog-to-digital converter, or A/D converter, or ADC for short, usually refers to an electronic device that converts an analog signal into a digital signal. Except for the most specialized analog-to-digital converters, all ADCs are implemented as integrated circuits (ICs). These are usually mixed-signal integrated circuit chips based on metal oxide semiconductor (MOS) that integrate analog and digital circuits.As we all know, ADC is mainly used to the digital acquisition of analog signals for for data processing purposes. The signals around us are generally continuously changing analog quantities, such as light, temperature, speed, pressure, sound, etc. However, most of us use digital equipment. If we want to use and process information easily, it is necessary to convert the analog quantity into a digital quantity and transmit it to the microcontroller or microprocessor. So how is ADC conversion realized? What kind of process is it? Reading the following note, you will definitely have a more comprehensive and systematic understanding of the analog-to-digital converter.What is ADC (Analog to Digital Converter)?CatalogIntroductionⅠ A/D Converter Basic1.1 Analog-to-Digital Converter Definition1.2 Analog to Digital Conversion Steps1.3 Why do We Need Analog-to-Digital Converter?Ⅱ Which A/D Converter is Better?Ⅲ What A/D Converter Includes?Ⅳ A/D Converter Applications and ICs4.1 Analog-to-Digital Converter Applications4.2 Analog-to-Digital Converter IC Modes ExplainedⅠ A/D Converter Basic1.1 Analog-to-Digital Converter DefinitionThe ADC converter is a system that converts analog signals into digital signals. It is a process of filtering, sample-and-hold, quantization and encoding. The analog signal passes band-limited filtering, sample-and-hold circuit, and becomes a ladder-shaped signal, and then passes through the encoder to make each level in the ladder-shaped signal become a binary code. Finally, the analog quantity is converted into a digital quantity and then transmitted to the CPU. That is to say, almost all energized data need ADC conversion. For example, electric energy metering of electric energy meters, weight measurement of electronic scales, temperature measurement of electronic thermometers, and communication fields.1.2 Analog to Digital Conversion StepsThe process of converting analog quantities into digital quantities is called analog-to-digital conversion, abbreviated as A/D, and the circuit that completes this function is called analog-to-digital converter, or ADC for short.Analog-to-Digital Conversion Steps Animation1) Sampling refers to replacing the original continuous signal in time with a sequence of signal samples at regular intervals, that is, discretizing the analog signal in time.2) Quantization uses a limited number of amplitude values to approximate the original continuously changing amplitude value, that is, changing the continuous amplitude of the analog signal into a limited number of discrete values with a certain interval.3) Encoding is based on a certain rule, the quantized value is represented by binary numbers, and then converted into a binary or multi-value digital signal stream. The digital signal obtained in this way can be transmitted through digital lines such as cables, microwave trunk lines, and satellite channels.The higher the signal frequency, the higher the operating frequency of the A/D circuit. The more digits, the more accurate the restoration accuracy of the signal. The I/O port of the MCU needs program cooperation to complete the A/D conversion. What’s more, the A/D chip can also be used alone to complete the analog-to-digital conversion.1.3 Why do We Need Analog-to-Digital Converter?Computer software, radio, and digital image acquisition all need the assistance of ADC converters, that is, the wave of human digitization has promoted the invention, development and continuous change of ADC converters. In short, the ADC converter plays an important role in human digitization.1) Many recording studios use 24-bit/96 kHz (or higher) pulse code modulation (PCM) or direct stream digital (DSD) recording formats, and then use ADC samples or decimates the signal for digital audio production on discs.2) Use ADC to store or transmit almost any analog signal in digital form. For example, TV tuner cards use fast video analog-to-digital converters. Digital storage oscilloscopes require very fast analog-to-digital converters, and ADCs are also crucial for software-defined radio and its new applications.3) Digital imaging systems usually use analog-to-digital converters to digitize pixels. Some radar systems usually use ADCs to convert signal strength into digital values for subsequent signal processing.4) Certain non-electronic or only partially electronic devices (such as rotary encoders) can also be regarded as analog-to-digital converters.Figure 1. Analog to Digital Conversion Example(Light Signal to Digital Signal) Ⅱ Which A/D Converter is Better?After years of development and continuous technological innovation, ADC converters have developed from Flash ADCs, Successive-Approximation ADCs, Counting/Slope Integration ADCs to sigma-delta (Σ-Δ) ADCs and Pipelined ADCs. They have their own advantages and disadvantages, and they can also meet different requirements.Successive-Approximation ADCs, Counting/Slope Integration ADCs and compression ADCs, etc. are mainly used in low-speed or medium-speed, medium-precision data acquisition and intelligent instruments. Hierarchical and pipelined ADCs are mainly used in high-speed signal processing, fast waveform storage and data recording, etc., such as video signal quantization and high-speed digital communication technology. ∑-△ ADC is mainly used in high-precision data acquisition, especially in electronic measurement fields such as digital sound systems, multimedia, seismic exploration instruments, sonar and so on. Here a brief description of the main ADC types is given below. Successive-Approximation ADCThe successive-approximation ADC is widely used. It includes a comparator, a digital-to-analog converter, a successive-approximation register (SAR) and a control logic unit. It is to continuously compare the sampling input signal with the known voltage. One clock cycle completes the 1-bit conversion, and the N-bit conversion requires N clock cycles. The conversion is completed and the output binary number is output. The resolution and sampling rate of this type ADC are contradictory: when the ADC resolution is low, the sampling rate is high, and if the resolution is to be improved, the sampling rate will be limited.Advantages: when the resolution is lower than 12 bits, the price is cheap, and the sampling rate can reach 1MSPS. Compared with other types, the power consumption is quite low.Disadvantages: In the case of higher than 14-bit resolution, the price is higher. The signal generated by the sensor needs to be conditioned before analog-to-digital conversion, including gain stage and filtering, so that the cost will increase significantly. Counting/Slope Integration ADCsCounting/Slope Integration ADC is also called dual-slope or multi-slope ADC, and its applications are also very wide. It is composed of an analog integrator with an input switch, a comparator and a counting unit. The input analog voltage is converted into a time interval proportional to its average value through two integrations. At the same time, a counter is used to count the clock pulses in this time interval, so as to realize the analog-to-digital conversion. Because the input end applies the integrator, it has a strong ability to suppress the interference of AC noise. For example, for high-frequency noise and fixed low-frequency (50Hz or 60Hz) interference suppression, it is suitable for use in noisy industrial environments. This type ADC is mainly used in low-speed, precision measurement and other fields, such as digital voltmeters.Advantages: High resolution, up to 22 bits; low power consumption and low cost.Disadvantages: The conversion rate is low, 100~300SPS at 12 bits. Parallel ADCsThe main feature of inter ADC is fast speed, which is the fastest of all types. The sampling rate can reach above 1GSPS. However, due to the limitations of power and volume, it is difficult to improve the resolution. The conversion of all bits of the ADC with this structure is completed at the same time, and the conversion time mainly depends on the switching speed of the comparator and the transmission time delay of the encoder. In addition, increasing the output code has little effect on the conversion time, but as the resolution increases, a high-density analog design  requires large number of precision divider resistors and comparator circuits for the conversion. That is to say, the output number is increased by one bit and the number of precision resistors is increased. It is about to double, and the comparator is also approximately doubled.The resolution of the parallel comparison ADC is limited by die size, input capacitance, power, etc. If the accuracy of the parallel comparators does not match, it will also cause static errors and increase the input offset voltage. Sigma-delta (Σ-Δ) ADCsThe Sigma-delta (Σ-Δ) ADC is composed of an integrator, a comparator, a 1-bit DA converter, and a digital filter. In principle, it is similar to the integral type. The input voltage is converted into a time (pulse width) signal and processed by a digital filter to obtain a digital value.Figure 2. Analog to Digital Converter Application ExampleⅢ What A/D Converter Includes?1) Sampling RateThe sampling rate indicates the rate at which the analog signal is converted into a digital signal, which is related to the manufacturing technology of the ADC device and depends on the judgment ability provided by the comparator in the ADC.Generally speaking, the sampling rate and resolution are mutually restrictive. Each time the sampling rate is doubled, the resolution losses 1bit. This is mainly due to the jitter during sampling, that is, aperture jitter or aperture uncertainty. 2) ADC ResolutionThe resolution indicates the number of bits after the analog signal is converted into a digital signal. It directly determines the quantization level of the ADC, that is, the minimum analog signal level value that the ADC can distinguish. Assuming that the ADC's input voltage range is (−V, V) and the resolution is N (bit), then the ADC has a 2N quantization level, so that the quantization level is: ΔV=2V/2N, where ΔV is the conversion accuracy. It can be seen from the above formula that the higher the resolution of the ADC and the smaller the voltage input range, the higher its conversion accuracy. 3) Signal-to-Noise Ratio (SNR)The signal-to-noise ratio (SNR) of the ADC reflects the ratio of the root mean square value of the noise-free signal part generated during the quantization process to the root mean square value of the quantization noise. If the input signal is a normalized sine wave 1/2sin(ωt+ψ), the SNR can be determined by the following formula: Among them, N is the resolution of ADC. It can be seen that the signal-to-noise ratio of the ADC mainly depends on the resolution. Every time the resolution increases by one bit, the SNR will increase by 6dB. However, as the resolution increases, the quantization level of the ADC becomes smaller, and the sampling process is more likely to be disturbed. 4) Effective Number of Bits (ENOB)ENOB is a measure of the dynamic range of an ADC converter. For the actual A/D conversion system, due to the influence of factors such as electrical noise, external interference, and non-linear distortion of analog circuits, it is not enough to measure system performance with ideal resolution. In order to better reflect the system performance, on the basis of the measured SNR, the above factors can be converted into quantization noise to get the ENOB. The calculation formula is as follows: ENOB is based on the equation for an ideal ADC's SNR: SNR = 6.02 × N + 1.76 dB, where N is the ADC's resolution.The difference between ENOB and ADC resolution reflects the degree of decrease in sampling accuracy caused by the decrease in SNR(here SNR caused by the error source). 5) Non-Linearity ErrorNon-linear error is an important accuracy index of the converter, which represents the difference between the actual conversion value of the ADC and the theoretical conversion value. Non-linear errors mainly include two types: Differential Non-Linearity (DNL) errors and Integral Non-Linearity (INL) errors. 6) Inter Modulation Distortion (IMD)When two sinusoidal signals are input to the ADC at the same time, due to the nonlinearity of the device, except the components of these two frequencies, the output spectrum will also produce many distortion products. The resulting distortion is called inter modulation distortion ( IMD, Inter Modulation Distortion), where the value of m+n represents the order of distortion. Among all inter-modulation distortions, the second-order and third-order inter-modulation products are the most important. The former is easily filtered out by a digital filter, while the latter is difficult to filter out. 7) Total Harmonic Distortion (THD)Due to the nonlinearity of the ADC, many high-order harmonics of the input signal appear in the output spectrum. These high-order harmonic components are called harmonic distortion components, and the resulting distortion is called Total Harmonic Distortion. Harmonic distortion and modulation distortion are two different concepts. The former is a distortion of the original signal waveform, even if a single frequency signal passes through the ADC, this phenomenon will occur, while the latter is mutual interference and influence between different frequencies.Figure 3. ADC on the ArduinoⅣ A/D Converter Applications and ICs4.1 Analog-to-Digital Converter ApplicationsMost ADC applications today belong to Four Segments: (a) Data acquisition(b) Precision industrial measurement(c) Voiceband and audio(d) High speed (sampling rates greater than about 5 MSPS)4.2 Analog-to-Digital Converter IC Modes ExplainedThere are many ADC ICs available in the market which can be used along to do conversion. Here lists several ADC ICs and their features and specifications as ADC selection references.⭕AD762116-Bit, 2 LSB INL, 3 MSPS PulSAR® ADC, High sampling rate, Available in a 48-lead LQFP or a 48-lead LFCSP⭕AD764118-Bit, 2 MSPS, Charge Redistribution SAR ADC 16 Bits Resolution with No Missing CodesNo Pipeline Delay ( SAR architecture )Differential Input Range: ±VREF (VREF up to 2.5V)Throughput:  3 MSPS (Wideband Warp and Warp Mode)  2 MSPS (Normal Mode)  1.25 MSPS (Impulse Mode)INL ±2 LSB Max (±30 ppm of FS)SINAD: 89 dB Typ @ 100 kHzTHD: -103 dB Typ @ 100 kHzParallel (16 or 8 bits bus) and Serial 5 V/3.3 V/2.5 V InterfaceSPI®/QSPI™/MICROWIRE™/DSP CompatibleOn-board Low Drift Reference with Buffer and Temperature SensorSingle 2.5 V Supply OperationPower Dissipation: 70 mW Typ @ 3 MSPS With REF18-bit resolution with no missing codes2.5 V internal low drift referenceThroughput:  2 MSPS (Warp mode)  1.5 MSPS (Normal mode)Differential input range: ± VREF (VREF up to 2.5 V)INL: ±2 LSB typicalNo pipeline delay (SAR architecture)Parallel (18-, 16-, or 8-bit bus)Serial 5 V/3.3 V/2.5 V interfaceSPI®/QSPI™/MICROWIRE™/DSP compatibleOn-board low drift reference with buffer and temperature sensor ⭕AD79088-Channel, 1 MSPS, 8-Bit ADC with Sequencer in 20-Lead TSSOP⭕AD79188-Channel, 1 MSPS, 10-Bit ADC with Sequencer in 20-Lead TSSOPFast throughput rate: 1 MSPSSpecified for AVDD of 2.7 V to 5.25 VLow Power:  6.0 mW max at 1 MSPS with 3 V supply  13.5 mW max at 1 MSPS with 5 V supplyEight (single-ended) inputs with sequencerWide input bandwidth: AD7928, 70 dB min SINAD at 50 kHz input frequencyFlexible power/serial clock speed managementNo pipeline delaysHigh speed serial interface SPI®/QSPI™/MICROWIRE™/DSP compatibleFast throughput rate: 1 MSPSSpecified for AVDD of 2.7 V to 5.25 VLow Power:  6.0 mW max at 1 MSPS with 3 V supply  13.5 mW max at 1 MSPS with 5 V supplyEight (single-ended) inputs with sequencerWide input bandwidth: AD7928, 70 dB min SINAD at 50 kHz input frequencyFlexible power/serial clock speed managementNo pipeline delaysHigh speed serial interface SPI®/QSPI™/MICROWIRE™/DSP compatible ⭕AD79288-Channel, 1 MSPS, 12-Bit ADC with Sequencer in 20-Lead TSSOP⭕AD5555Precision DUAL 16-Bit 14-Bit-DACs in Compact TSSOP PackagesFast throughput rate: 1 MSPSSpecified for AVDD of 2.7 V to 5.25 VLow Power:  6.0 mW max at 1 MSPS with 3 V supply  13.5 mW max at 1 MSPS with 5 V supplyEight (single-ended) inputs with sequencerWide input bandwidth: AD7928, 70 dB min SINAD at 50 kHz input frequencyFlexible power/serial clock speed managementNo pipeline delaysHigh speed serial interface SPI®/QSPI™/MICROWIRE™/DSP compatible14-bit resolution±1 LSB DNL monotonic±1 LSB INL2 mA full-scale current ±20%, with VREF = 10 V0.5 μs settling time2Q multiplying reference-input 6.9 MHz BWZero or midscale power-up presetZero or midscale dynamic reset3-wire interfaceCompact TSSOP-16 package ⭕AD823016 V Rail-to-Rail, Zero-Drift, Precision Instrumentation Amplifier⭕AD77993-Channel, Low Noise, Low Power, 24-Bit, Sigma Delta ADC with On-Chip In-AmpResistor programmable gain range: 101 to 1000Supply voltage range: ±4 V to ±8 VRail-to-rail input and outputMaintains performance over −40°C to +125°CExcellent ac and dc performance  110 dB minimum CMR @ 60 Hz, G = 10 to 1000  10 μV maximum offset voltage (RTI, ±5 V operation)  50 nV/°C maximum offset drift  20 ppm maximum gain nonlinearityRMS noise:  27 nV at 4.17 Hz (AD7799)  65 nV at 16.7 Hz (AD7799)  40 nV at 4.17 Hz (AD7798)  85 nV at 16.7 Hz (AD7798)Current: 380 μA typicalPower-down: 1 μA maximumLow noise, programmable gain, instrumentation ampUpdate rate: 4.17 Hz to 470 Hz 3 differential inputsInternal clock oscillatorSimultaneous 50 Hz/60 Hz rejectionReference detectLow-side power switchProgrammable digital outputsBurnout currentsPower supply: 2.7 V to 5.25 V ⭕AD944414-Bit, 80 MSPS A/D Converter⭕AD944514-Bit, 105 MSPS / 125 MSPS A/D Converter80 MSPS guaranteed sampling rate100 dB two-tone SFDR with 69.3 MHz and 70.3 MHz73.1 dB SNR with 70 MHz input97 dBc SFDR with 70 MHz inputExcellent linearity  DNL = ±0.4 LSB typical  INL = ±0.6 LSB typical1.2 W power dissipation3.3 V and 5 V supply operation2.0 V p-p differential full-scale inputLVDS outputs (ANSI-644 compatible)Data format selectOutput clock available125 MSPS guaranteed sampling rate (AD9445BSV-125)100 dB two-tone SFDR with 30 MHz and 31 MHz73.5 dB SNR with 70 MHz input85 dBc SFDR with 225 MHz inputExcellent linearity  DNL = ±0.25 LSB typical  INL = ±0.8 LSB typical2.3 W power dissipation3.3 V and 5 V supply operation2.0 V p-p to 3.2 V p-p differential full-scale inputLVDS outputs (ANSI-644 compatible) or CMOS outputsData format select (Offset Binary or 2’s compliment)Output clock available ⭕AD944616-Bit, 80 MSPS / 100 MSPS A/D Converter⭕AD923512-Bit, 20/40/65 MSPS, 3 V Analog-to-Digital Converter100 MSPS guaranteed sampling rate (AD9446-100)83.6 dBFS SNR with 30 MHz input(3.8 V p-p input, 80 MSPS)82.6 dBFS SNR with 30 MHz input(3.2 V p-p input, 80 MSPS)89 dBc SFDR with 30 MHz input(3.2 V p-p input, 80 MSPS)95 dBFS 2-tone SFDR with 9.8 MHz and10.8 MHz (100 MSPS)l 60 fsec rms jitterExcellent linearity  DNL = DNL = ±0.4 LSB typical  INL = ±3.0 LSB typical2.0 V p-p to 4.0 V p-p differential full-scale inputBuffered analog inputsLVDS outputs (ANSI-644 compatible) or CMOS outputsData format select (offset binary or twos complement)Output clock available3.3 V and 5 V supply operationSingle +3 V Supply Operation (2.7 V to 3.6 V)SNR = 70 dBc to Nyquist at 65 MSPSSFDR = 85 dBc to Nyquist at 65 MSPSLow Power: 300 mW at 65 MSPSOn-Chip Reference and SHADifferential Input with 500 MHz BandwidthDNL of ±0.4 LSBFlexible Analog Input: 1 V p-p to 2 V p-pOffset Binary or Twos Complement Data FormatClock Duty Cycle StabilizerPin out Migration to Either AD9215, AD9236, AD9245 Frequently Asked Questions about Analog to Digital Converter (ADC Basic)1. What is the use of analog to digital converter?Analog-to-digital converters, abbreviated as “ADCs,” work to convert analog (continuous, infinitely variable) signals to digital (discrete-time, discrete-amplitude) signals. In more practical terms, an ADC converts an analog input, such as a microphone collecting sound, into a digital signal. 2. What are the types of analog to digital converters?There are really five major types of ADCs in use today:Successive Approximation (SAR) ADCDelta-sigma (ΔΣ) ADCDual Slope ADCPipelined ADCFlash ADC 3. Which chip is used in analog to digital?An A/D converter is used to convert an analog signal like voltage to digital form so that it can be read and processed by a microcontroller. Some microcontrollers have built-in A/D converters. It is also possible to connect an external A/D converter to any type of microcontroller. 4. Which circuit is used in analog to digital converter?Analog to Digital Converter (ADC) is an electronic integrated circuit used to convert the analog signals such as voltages to digital or binary form consisting of 1s and 0s. Most of the ADCs take a voltage input as 0 to 10V, -5V to +5V, etc., and correspondingly produces digital output as some sort of a binary number.

Ⅰ IntroductionIn an analog world surrounded by digital devices, we exist in a fascinating intersection of two domains. In nature, everything we observe, feel, or measure is analog—such as light, temperature, speed, pressure, and sound. However, most electronic devices around us are digital, ranging from basic digital watches to sophisticated supercomputers and AI systems. Therefore, for microcontrollers, microprocessors, and modern computing systems to understand and process real-world phenomena, we need devices that can convert these analog parameters into digital values. This conversion is performed by an ADC (Analog-to-Digital Converter), and in this comprehensive guide, we will explore their functionality, types, and applications in modern electronics.Ⅱ Definition of ADC (Analog-to-Digital Converter)An Analog-to-Digital Converter (ADC) is a circuit that converts continuous voltage values (analog signals) into binary values (digital data) that can be interpreted and processed by digital computers and microcontrollers. These ADC circuits can be found as standalone integrated circuits (ICs) or embedded within microcontrollers, system-on-chip (SoC) designs, and digital signal processors (DSPs). The conversion process involves sampling the analog signal at discrete time intervals and quantizing the amplitude into digital codes.Modern ADCs are fundamental components in virtually all electronic systems that interface with the physical world, from smartphones and IoT devices to medical equipment and automotive sensors.Ⅲ The Reasons for Using ADCsToday's electronics ecosystem is predominantly digital; the era of analog computers has long passed. However, the physical world we inhabit remains inherently analog and continuous. Digital systems can only process discrete values—essentially ones and zeros—which creates a fundamental incompatibility with analog signals.For example, a temperature sensor such as the LM35 outputs a temperature-dependent voltage—specifically, 10 mV per degree Celsius. If we connect this directly to a digital input pin, the microcontroller will only register it as either HIGH or LOW based on threshold voltages (typically around 0.8V for LOW and 2V for HIGH in 5V systems), which provides no useful temperature information. Instead, we use an ADC to convert the analog voltage input into a multi-bit digital value that can be directly processed by the microprocessor's data bus, enabling precise calculations, data logging, and control decisions.Key reasons for using ADCs include:Enabling digital processing of real-world analog signalsFacilitating data storage and transmission in digital formatAllowing complex mathematical operations on sensor dataEnabling machine learning and AI applications with sensor inputsProviding noise immunity through digital signal processingⅣ Working Principles of ADCUnderstanding ADC operation is best approached by viewing it as a mathematical mapping function. The ADC maps continuous analog voltage values to discrete binary numbers within a defined range. This process involves three fundamental steps: sampling, quantization, and encoding.The ADC needs to bridge the gap between the analog voltage domain and the digital logic domain. Since digital registers can only accept discrete logic levels (HIGH/LOW), directly connecting an analog signal would produce unreliable results. The ADC acts as an intelligent interface that periodically samples the analog input and converts each sample into a binary representation.Figure 1: Analog to Digital Conversion ProcessHere are the essential characteristics of ADCs that determine their performance and suitability for different applications:4.1 Reference VoltageNo ADC operates in absolute terms; instead, it requires a reference voltage that defines the full-scale range. The reference voltage represents the maximum analog input that corresponds to the highest possible digital output value. For example, in a 10-bit converter with a 5V reference voltage, the binary value 1111111111 (1023 in decimal—the highest possible 10-bit number) corresponds to 5V, while 0000000000 (0 in decimal) corresponds to 0V.Since 10 bits provide 210 = 1024 possible values (0-1023), each binary step represents approximately 5V / 1024 ≈ 4.88 mV. This measure is called the resolution or LSB (Least Significant Bit) voltage of the ADC. The formula is:Resolution (V) = VREF / 2nwhere VREF is the reference voltage and n is the number of bitsIf the analog voltage changes by less than one LSB (4.88mV in this example), the ADC cannot detect the change—this creates a quantization error. To minimize this error and improve measurement precision, you can either use an ADC with higher resolution (more bits) or reduce the reference voltage to match your signal range more closely.Modern ADCs are available with resolutions ranging from 8 bits (256 levels) for simple applications to 32 bits (over 4 billion levels) for precision scientific instruments, though 12-bit and 16-bit converters are most common in embedded systems.4.2 Sample Rate (Sampling Speed)The sample rate, also called sampling frequency, refers to the number of analog-to-digital conversions the ADC performs per second, measured in samples per second (S/s or SPS). High-performance ADCs can achieve sample rates exceeding 1 GS/s (giga-samples per second, or one billion samples per second), while precision ADCs might operate at just a few samples per second.According to the Nyquist-Shannon sampling theorem, to accurately reconstruct a signal, the sampling rate must be at least twice the highest frequency component in the signal. For example, to digitize audio signals with frequencies up to 20 kHz, you need a sampling rate of at least 40 kHz (which is why CD audio uses 44.1 kHz).The sampling speed depends on the ADC architecture and the required accuracy. Generally, there's a trade-off between speed and resolution: high-speed ADCs (like flash ADCs) typically have lower resolution (8-10 bits), while high-resolution ADCs (like sigma-delta ADCs) operate at lower speeds. This is because achieving higher precision requires more time to accurately measure and convert the analog signal.4.3 Additional Key SpecificationsSignal-to-Noise Ratio (SNR): Measures the ratio of the desired signal power to background noise, typically expressed in decibels (dB). Higher SNR indicates better performance.Effective Number of Bits (ENOB): Accounts for real-world imperfections and indicates the actual resolution achieved in practice, which is typically less than the nominal bit count.Input Impedance: The electrical resistance presented by the ADC input, which affects how it loads the source circuit. High input impedance is generally desirable to minimize signal distortion.Ⅴ Types of ADCsVarious ADC architectures have been developed to optimize for different combinations of speed, resolution, power consumption, and cost. Here are the most common types:5.1 Flash ADCs (Parallel ADCs)Flash ADCs are the fastest type of analog-to-digital converter, capable of conversion rates exceeding 1 GS/s. They consist of a resistor ladder voltage divider and an array of comparators—one for each quantization level. For an n-bit flash ADC, 2n - 1 comparators are required.Figure 2: Flash ADC ArchitectureAll comparators operate simultaneously (in parallel), comparing the input voltage against their respective reference levels. The comparator outputs are then fed through a priority encoder that converts the thermometer code into binary format. The conversion speed is limited only by the propagation delays of the comparators and encoder, making flash ADCs ideal for high-speed applications like video processing and radar systems.Advantages: Extremely fast, simple operationDisadvantages: High power consumption, large chip area, limited resolution (typically 8-10 bits due to exponential growth in component count), expensive for high-resolution designs5.2 Successive Approximation Register (SAR) ADCsSAR ADCs are among the most popular and widely used converters, offering an excellent balance between speed, resolution, and power consumption. They consist of a sample-and-hold circuit, a comparator, a Digital-to-Analog Converter (DAC), and successive approximation logic.The conversion process uses a binary search algorithm. Starting with the most significant bit (MSB), the SAR sets each bit to '1' and compares the DAC output with the input voltage. If the DAC output exceeds the input, the bit is cleared to '0'; otherwise, it remains '1'. This process repeats for each bit from MSB to LSB, requiring n clock cycles for an n-bit conversion.SAR ADCs are ubiquitous in microcontrollers (including Arduino, STM32, ESP32, and most ARM Cortex-M devices) and can achieve resolutions from 8 to 18 bits with sampling rates from 100 kS/s to several MS/s.Advantages: Good resolution, moderate speed, low power consumption, cost-effectiveDisadvantages: Slower than flash ADCs, requires n clock cycles for n-bit conversion5.3 Sigma-Delta (ΣΔ) ADCsSigma-delta ADCs achieve very high resolution (16 to 32 bits) by using oversampling and noise-shaping techniques. They sample the input at a rate much higher than the Nyquist rate and use digital filtering to achieve high effective resolution at lower output data rates.These converters are ideal for precision measurement applications such as digital scales, industrial sensors, audio recording equipment, and medical instrumentation where accuracy is paramount and speed is less critical.Advantages: Excellent resolution and linearity, good noise rejection, simple analog circuitryDisadvantages: Slow conversion rate, complex digital filtering required, higher latency5.4 Dual-Slope (Integrating) ADCsDual-slope ADCs integrate the input signal for a fixed period, then integrate a reference voltage of opposite polarity until the integrator returns to zero. The time required for the second integration is proportional to the input voltage. A counter measures this time, providing the digital output.While slow, dual-slope ADCs offer excellent noise rejection (especially for 50/60 Hz line frequency noise) and are commonly used in digital multimeters and panel meters.Advantages: High accuracy, excellent noise rejection, low costDisadvantages: Very slow conversion speed, typically limited to a few conversions per second5.5 Pipeline ADCsPipeline ADCs divide the conversion into multiple stages, with each stage resolving a few bits. The residue from each stage is amplified and passed to the next stage. This architecture allows for high sampling rates (10-100 MS/s) with moderate resolution (8-16 bits), making them popular in video processing, communications, and imaging applications.Ⅵ Applications of ADCs6.1 Digital Oscilloscopes and MultimetersWhile analog oscilloscopes provide real-time display with minimal processing delay, they cannot store waveforms, perform automated measurements, or conduct advanced signal analysis. Digital oscilloscopes solve these limitations by employing high-speed, high-resolution ADCs (typically 8-12 bits at sampling rates up to several GS/s).Modern digital oscilloscopes can capture transient events, perform FFT analysis, decode serial protocols, and store thousands of waveforms for later analysis. Similarly, digital multimeters use precision ADCs (often dual-slope or sigma-delta types) to provide accurate voltage, current, and resistance measurements with 3½ to 8½ digit resolution.6.2 Microcontrollers and Embedded SystemsNearly all modern microcontrollers include integrated ADCs, making them essential for IoT devices, sensor interfaces, and embedded control systems. Common examples include:Arduino (ATmega328P): 10-bit SAR ADC, 6 channels, up to 15 kS/sSTM32 series: 12-bit SAR ADC, multiple channels, up to 5 MS/s (varies by model)ESP32: 12-bit SAR ADC, 18 channels, up to 2 MS/sRaspberry Pi Pico (RP2040): 12-bit SAR ADC, 4 channels, 500 kS/sNordic nRF52 series: 12-bit SAR ADC for low-power wireless applicationsThe Arduino IDE provides a convenient analogRead() function that reads an analog voltage on any analog input pin and returns a 10-bit integer value (0-1023), making ADC usage accessible even for beginners.6.3 Digital Power Supplies and Battery ManagementModern programmable power supplies and battery management systems rely heavily on ADCs to monitor output voltage, current, and temperature. These measurements enable precise regulation, protection features, and user interfaces displaying real-time parameters. High-resolution ADCs (16-24 bits) are often used in precision laboratory power supplies to achieve millivolt-level accuracy.6.4 Audio Recording and ProcessingProfessional audio equipment uses high-quality sigma-delta ADCs with 24-bit resolution and sampling rates of 44.1 kHz, 48 kHz, 96 kHz, or even 192 kHz. These converters enable digital recording, processing, and storage of audio signals with exceptional fidelity. Consumer devices like smartphones and laptops also incorporate audio ADCs for voice recording and communication.6.5 Medical InstrumentationMedical devices such as ECG monitors, pulse oximeters, blood glucose meters, and patient monitoring systems all depend on precision ADCs to convert physiological signals into digital data for analysis, display, and storage. These applications demand high accuracy, low noise, and often require specialized ADCs designed for biomedical signals.6.6 Automotive and Industrial SensorsModern vehicles contain hundreds of sensors monitoring engine parameters, emissions, tire pressure, temperature, acceleration, and more—all requiring ADCs for digital processing. Industrial automation similarly relies on ADCs for process control, quality monitoring, and predictive maintenance applications.Ⅶ How to Use External ADC ICsWhen the built-in ADC of a microcontroller doesn't meet your requirements—whether due to insufficient resolution, speed, or channel count—external ADC ICs provide a solution. Popular external ADC modules include the ADS1115, MCP3008, AD7606, and ADS1256, which can be interfaced with microcontrollers, Raspberry Pi, and other digital systems.Let's examine the Texas Instruments ADS1115, a popular 16-bit ADC with advanced features and excellent performance:Figure 3: ADS1115 16-bit ADC Module7.1 Key Features of Modern ADC ICsI²C/SPI Interface: The ADS1115 uses the I²C bus for communication, making it easy to interface with Arduino, Raspberry Pi, ESP32, and other platforms. Extensive libraries are available in multiple programming languages, simplifying implementation. The I²C interface also allows multiple ADCs to share the same bus using different addresses.Low Power Consumption: Modern ADC ICs are designed for efficiency, with the ADS1115 consuming only 150 µA in continuous conversion mode and less than 1 µA in power-down mode. The operating voltage range of 2.0V to 5.5V makes it compatible with both 3.3V and 5V systems.Programmable Gain Amplifier (PGA): The ADS1115 includes a built-in PGA with selectable gain settings (±6.144V, ±4.096V, ±2.048V, ±1.024V, ±0.512V, ±0.256V), allowing you to optimize the measurement range for your signal amplitude and maximize resolution.Flexible Input Configuration: The four analog inputs can be configured as four single-ended inputs or two differential pairs, providing versatility for different measurement scenarios. Differential inputs are particularly useful for rejecting common-mode noise.Programmable Comparator: An integrated comparator with programmable thresholds can generate interrupts when the input exceeds specified limits, enabling efficient event-driven programming without continuous polling.High Resolution: With 16-bit resolution, the ADS1115 provides 65,536 discrete levels, offering significantly better precision than typical 10-bit or 12-bit microcontroller ADCs. At the ±4.096V range, this translates to approximately 125 µV per step.Ⅷ Limitations and Considerations of ADCsWhile ADCs are essential components, they do have inherent limitations that designers must consider:Conversion Time: ADCs require finite time to perform conversions, ranging from nanoseconds (flash ADCs) to milliseconds (high-resolution sigma-delta ADCs). This introduces latency that may be problematic in real-time control systems.Quantization Error: The discrete nature of digital representation means that analog values between quantization levels cannot be precisely represented, introducing an inherent error of up to ±½ LSB.Aliasing: If the input signal contains frequency components above half the sampling rate (Nyquist frequency), aliasing occurs, causing high-frequency signals to appear as lower frequencies in the digital output. Anti-aliasing filters are required to prevent this.Noise and Interference: ADCs are sensitive to electrical noise, which can degrade measurement accuracy. Proper PCB layout, grounding, filtering, and shielding are essential for optimal performance.Input Impedance Effects: The ADC input impedance can load the source circuit, potentially affecting the signal being measured. Buffer amplifiers may be necessary for high-impedance sources.Cost and Complexity: High-performance ADCs (high resolution and high speed) are expensive and may require complex supporting circuitry, including precision voltage references, low-noise power supplies, and sophisticated digital signal processing.Power Consumption: High-speed ADCs can consume significant power, which may be problematic in battery-powered or energy-constrained applications.Ⅸ Frequently Asked Questions (FAQ)1. Why do we need an ADC converter?The physical world is inherently analog—sound waves, light, temperature, pressure, and other phenomena exist as continuous values. However, digital computers and microcontrollers can only process discrete binary numbers (ones and zeros). ADCs bridge this gap by sampling analog signals and converting them into digital representations that computers can store, process, and analyze. This enables applications ranging from digital audio recording and sensor data logging to medical diagnostics and industrial automation. Without ADCs, modern digital systems would be unable to interact with or measure real-world phenomena.2. What is the slowest type of ADC?Dual-slope (integrating) ADCs are among the slowest, typically performing only a few conversions per second. However, this slow speed is often intentional—these ADCs integrate the signal over a long period, which provides excellent noise rejection, particularly for 50/60 Hz power line interference. They're commonly used in digital multimeters where accuracy is more important than speed. Sigma-delta ADCs can also be quite slow when configured for maximum resolution, though they offer superior performance compared to dual-slope designs.3. What is the difference between 8-bit, 10-bit, and 12-bit ADCs?The bit count determines the resolution—how finely the ADC can divide the voltage range. An 8-bit ADC provides 256 discrete levels (2⁸), a 10-bit ADC provides 1,024 levels (2¹⁰), and a 12-bit ADC provides 4,096 levels (2¹²). With a 5V reference: an 8-bit ADC has ~19.5 mV per step, a 10-bit ADC has ~4.9 mV per step, and a 12-bit ADC has ~1.2 mV per step. Higher resolution allows detection of smaller voltage changes, making the measurement more precise. However, higher resolution often comes with trade-offs in speed, cost, and complexity. Choose the resolution based on your application's accuracy requirements.4. What is the difference between ADC and DAC?An ADC (Analog-to-Digital Converter) is an input device that converts continuous analog signals into discrete digital values for processing by digital systems. A DAC (Digital-to-Analog Converter) performs the opposite function—it's an output device that converts digital values into continuous analog signals. For example, when recording audio, an ADC converts sound waves (analog) into digital data; when playing back that audio, a DAC converts the digital data back into analog signals that drive speakers. Both are essential for digital systems to interact with the analog world.5. How does the ADC inside a microcontroller work?Most microcontrollers use SAR (Successive Approximation Register) ADCs due to their good balance of speed, resolution, and power efficiency. The process involves: (1) A sample-and-hold circuit captures and holds the input voltage stable during conversion; (2) The SAR logic performs a binary search, testing each bit from MSB to LSB by comparing the input against a DAC output; (3) After n clock cycles (for n bits), the final binary value is stored in a register where the CPU can read it. The entire process typically takes a few microseconds, and many microcontrollers can perform conversions automatically in the background using DMA (Direct Memory Access).6. How do you convert analog to digital?The conversion process involves three main steps: (1) Sampling: The continuous analog signal is measured at discrete time intervals determined by the sampling rate; (2) Quantization: Each sampled voltage value is mapped to the nearest discrete level based on the ADC's resolution; (3) Encoding: The quantized level is represented as a binary number. The sampling rate must be at least twice the highest frequency in the signal (Nyquist theorem) to avoid aliasing, and the resolution must be sufficient to capture the required detail in the amplitude.7. Why do we need to convert analog to digital?Digital representation offers numerous advantages: (1) Processing: Digital signals can be easily manipulated using algorithms, filters, and mathematical operations; (2) Storage: Digital data can be stored indefinitely without degradation; (3) Transmission: Digital signals are less susceptible to noise and interference during transmission; (4) Accuracy: Digital systems can perform precise calculations and measurements; (5) Integration: Digital data can be easily shared between different systems and processed by computers; (6) Advanced Features: Digital signals enable machine learning, pattern recognition, and sophisticated analysis impossible with analog systems.8. What are common applications of ADCs?ADCs are used in countless applications: digital oscilloscopes and multimeters for test equipment; microcontrollers and embedded systems for sensor interfaces; audio recording and playback equipment; medical devices (ECG, pulse oximeters, blood pressure monitors); automotive sensors (engine management, safety systems); industrial process control; telecommunications equipment; digital cameras and imaging systems; touchscreen interfaces; battery management systems; smart home devices and IoT sensors; scientific instrumentation; and data acquisition systems. Essentially, any application requiring a digital system to measure or respond to analog phenomena requires an ADC.9. What's the difference between analog and digital signals?Analog signals are continuous in both time and amplitude—they can take any value within a range and change smoothly over time. Examples include sound waves, temperature variations, and light intensity. Digital signals are discrete in both time and amplitude—they exist only at specific time intervals (samples) and can only take specific values (quantization levels). Digital signals are typically represented as binary numbers (sequences of 1s and 0s). While analog signals directly represent physical phenomena, digital signals are representations that approximate the analog world in a form that computers can process.10. What factors should I consider when choosing an ADC?Key selection criteria include: (1) Resolution: How many bits are needed for your accuracy requirements? (2) Sampling Rate: How fast must you sample to capture your signal's frequency content? (3) Input Range: Does it match your signal amplitude? (4) Number of Channels: How many signals need to be measured? (5) Interface: SPI, I²C, parallel, or integrated? (6) Power Consumption: Critical for battery-powered applications; (7) Cost: Balance performance with budget; (8) Package Size: PCB space constraints; (9) Input Type: Single-ended or differential? (10) Additional Features: Built-in PGA, reference, comparator, etc. Consider your application's priorities—speed, accuracy, power, or cost—and choose accordingly.Ⅹ ConclusionAnalog-to-Digital Converters are fundamental building blocks of modern electronics, serving as the essential bridge between our analog physical world and the digital systems that process information. From the simplest temperature sensor in a home thermostat to the sophisticated signal processing in medical imaging equipment, ADCs enable digital systems to perceive, measure, and respond to real-world phenomena.Understanding ADC specifications—resolution, sampling rate, input range, and architecture—is crucial for selecting the right converter for your application. Whether you're using the built-in ADC in a microcontroller for a hobby project or designing a precision measurement system with external high-resolution ADCs, the principles remain the same: sample the analog world accurately and convert it to digital form for processing.As technology advances, ADCs continue to improve in resolution, speed, and power efficiency while decreasing in cost and size. This ongoing evolution enables new applications in IoT, wearable devices, autonomous vehicles, and countless other fields where the digital and analog worlds intersect.Last Updated: November 2025

The LTC2185 is a 125Msps 16-bit ADC with excellent noise and linearity performance while only consuming 185mW per channel. It is ideal for demanding low power applications that require excellent AC performance. A high performance ADC like the LTC2185 requires a high performance amplifier driving it to maintain the excellent performance. The ADA4927-1 delivers the linearity performance required by the LTC2185 while only consuming 215mW. The well designed package of the ADA4927-1 allows for a simple layout that reduces parasitic capacitance in the feedback path that can erode the phase margin of the amplifier. This combination of ADC and driver allows excellent performance from 62.5-125MHz a region where other high speed amplifiers are lacking.  The LTC2185 is a two-channel simultaneous sampling parallel ADC which offers a choice of full-rate CMOS, or double data rate (DDR) CMOS/LVDS digital outputs. Pin-compatible speed grade options include 25Msps, 40Msps, 65Msps, 80Msps and 105Msps with approximate power dissipation of just 1.5mW/Msps per channel. It includes popular features such as the digital output randomizer and alternate bit polarity (ABP) mode that minimize digital feedback when using parallel CMOS outputs.  Analog full power bandwidth of 550MHz and ultralow jitter of 0.07psRMS allows under-sampling of IF frequencies with excellent noise performance. To maintain this level of performance the LTC2185 needs to be driven with an appropriate amplifier like the ADA4927-1. The ADA4927 is a high speed differential current feedback amplifier. Fabricated on Analog Devices’ silicon-germanium process, the ADA4927-1 has excellent distortion and an input voltage noise of only 1.3nV/rtHz. This allows it to drive high speed ADCs like the LTC2185. The gain of the ADA4927-1 is set with external feedback resistors located next to the input pins.  By keeping the feedback pins and input pins close on the package, the ADA4927-1 provides a clean layout and minimizing the parasitic capacitance in the feedback network. This make the ADA4927-1 an ideal choice for driving high performance ADCs, like the LTC2185, from DC to 125 MHz. Figure 1 shows a schematic of the ADA4927-1 driving the LTC2185. The corresponding layout is shown in figure 2.  The feedback pins on the ADA4927-1 are adjacent to the input pins which minimizes the parasitic capacitance of the feedback node and improves the phase margin of the amplifier. It also Simplifier the layout by making it possible to place feedback resistors directly across the two pins and not having additional trace length in the feedback path. There is a simple filter between the amplifier and ADC that reduces the wideband noise of the amplifier and improves the SNR of the system. This filter also attenuates the sampling glitches from the ADC before they reach the amplifier. This helps keep the output network of the ADA4927 from oscillating in response to these glitches. This filter network can be modified to accommodate a wide range of input bandwidth requirements. (Figure 1:  Schematic showing an ADA4927-1 driving one channel of the LTC2185)(Figure 2:  Layout showing an ADA4927-1 driving once channel of the LTC2185)Figure 3 and figure 4 show the SNR and SFDR of the LTC2185 and ADA4927-1 combination. The SFDR stays above 67dB out to 125MHz while the SNR is better than 63dB to the same frequency. This combination only consumes 250mW. With a sample rate of 125Msps, this combination provides good performance through the entire 2nd Nyquist zone where other amplifiers begin to have poor linearity.  (Figure 3:  SNR of the LTC2185 driven with the ADA4927-1)(Figure 4:  SFDR of the LTC2185 driven with the ADA4927-1) Using the ADA4927-1 to drive the LTC2185 provides excellent linearity while keeping the power consumption low. The fact that the ADA4927-1 stays very linear out to 125MHz allows this ADC amplifier combination to be used in demanding communication and medical applications that require the use of the second Nyquist zone of the LTC2185. The pin out of the ADA4927-1 and filter design minimize the complexity of the layout while maintaining excellent performance on a low power budget. Ref.KY32-LTC2185KY362-ADA4927-1