Products >> Analog signal chain chip >> Data converter AD, D/A

Analog-to-Digital Converter (A/D)
- Definition and Function
  - The analog-to-digital converter (Analog-to-Digital Converter, abbreviated as A/D or ADC) is an electronic device or circuit used to convert analog signals into digital signals. Its main function is to sample the continuously changing analog signal (such as voltage, current, etc.) and quantize the sampled value into a digital code, so that the analog signal can be stored, processed and transmitted in a digital system (such as a computer, digital signal processor, etc.). For example, in the audio recording process, the analog audio signal output by the microphone needs to be converted into a digital signal by an analog-to-digital converter before it can be stored in a digital audio device.
- Working Principle
  - Sampling: Sample the analog signal at certain time intervals to obtain the instantaneous value of the analog signal at each sampling moment. The sampling frequency determines the sampling fineness of the analog signal. According to the Nyquist-Shannon sampling theorem, in order to completely restore the original analog signal, the sampling frequency should be at least twice the highest frequency of the analog signal. For example, for an analog signal with a maximum frequency of 1kHz, the sampling frequency needs to be at least 2kHz.
  - Quantization: Convert the sampled instantaneous value of the analog signal into a discrete digital value. This is achieved by dividing the amplitude range of the analog signal into multiple quantization intervals, and each quantization interval corresponds to a specific digital code. The quantization process will introduce quantization error, and the magnitude of the quantization error depends on the size of the quantization interval and the quantization method.
  - Encoding: Convert the quantized digital value into a binary code that can be recognized and processed by the digital system. Commonly used encoding methods include two's complement code, Gray code, etc.
- Main Types
  - Successive Approximation Register (SAR) ADC: This is a relatively common type of analog-to-digital converter. It determines the digital output by successively comparing the analog input signal with the internal reference voltage. This type of ADC has moderate conversion speed and high resolution, and is suitable for many medium-speed data acquisition applications with high precision requirements, such as industrial process control, instrumentation, etc.
  - Integrating ADC: Use an integrator to integrate the analog input signal, and then realize conversion by comparing the integration result with the reference voltage. The advantage of the integrating ADC is its strong anti-interference ability, especially for low-frequency interference such as power supply noise. It is often used for low-speed signal conversion with extremely high precision requirements, such as digital voltmeters and other equipment.
  - Flash ADC: It has a very high conversion speed. It realizes rapid conversion by parallel comparison of multiple reference voltages and analog input signals. However, this type of ADC has relatively low resolution, and as the resolution increases, the circuit complexity and cost will increase sharply. It is mainly used in occasions with extremely high speed requirements, such as high-speed communication and radar signal processing.
- Main Characteristics
  - Resolution: Refers to the minimum analog signal change that the analog-to-digital converter can distinguish, usually expressed in bits. For example, a 12-bit ADC can distinguish a smaller minimum voltage change than an 8-bit ADC, and has a higher resolution. The resolution determines the degree to which the converted digital signal can accurately represent the analog signal.
  - Conversion speed: That is, the number of analog-to-digital conversions that can be completed per unit time, usually measured in samples per second (SPS). The speed of conversion determines the frequency range of the analog signal that the ADC can handle. For analog signals that change rapidly, an ADC with a high conversion speed is required.
  - Linearity: Describes the degree of linear relationship between the output digital code of the ADC and the input analog signal. Good linearity can ensure that the converted digital signal can accurately reflect the change of the analog signal and reduce distortion.
- Application Fields
  - Audio processing field: In audio recording and playback devices, convert analog audio signals into digital audio signals for storage and processing, or convert digital audio signals back to analog audio signals for playback. For example, analog-to-digital converters are indispensable in devices such as digital audio workstations and MP3 players.
  - Communication field: Used to convert received analog communication signals (such as radio frequency signals, baseband signals, etc.) into digital signals for processing in digital communication systems, such as in mobile phone base stations, communication terminals and other devices.
  - Industrial measurement and control field: Convert the analog signals output by various industrial sensors (such as temperature, pressure, flow, etc.), and then input the digital signals into the controller or computer for analysis and control to realize the automatic control of industrial processes.
Digital-to-Analog Converter (D/A)
- Definition and Function
  - The digital-to-analog converter (Digital-to-Analog Converter, abbreviated as D/A or DAC) is an electronic device or circuit that converts digital signals into analog signals. Its main function is to convert the digital code in the digital system into the corresponding continuous analog signal (such as voltage, current, etc.), so that the digital signal can drive analog devices (such as speakers, motors, etc.) or be used for the control of analog systems. For example, in an audio playback system, the digital audio signal stored in a digital device needs to be converted into an analog audio signal by a digital-to-analog converter before it can drive the speaker to make a sound.
- Working Principle
  - Decoding: First decode the input digital signal to determine the analog signal value corresponding to each digital code. This is realized based on the decoding circuit inside the digital-to-analog converter. Different decoding methods will produce different analog outputs.
  - Conversion: According to the analog signal value obtained by decoding, convert the digital signal into an analog signal through a resistor network, capacitor network or other conversion circuits. For example, in a commonly used binary weighted resistor network digital-to-analog converter, resistors of different resistances are connected to each bit of the digital signal, and the current distribution is controlled according to the value of each bit of the digital signal to generate an analog voltage output.
- Main Types
  - Binary weighted resistor type DAC: This type of DAC uses a binary weighted resistor network to realize the conversion from digital signal to analog signal. Its structure is relatively simple and the principle is intuitive. However, as the resolution increases, the value range of the resistors will become very wide, making it difficult to ensure the accuracy of the resistors and being more sensitive to environmental factors such as temperature.
  - R-2R ladder resistor type DAC: Conversion is performed through an R-2R resistor ladder network. Its advantage is that there are only two resistance values, which is convenient to achieve high-precision matching and is less sensitive to environmental changes such as temperature. This type of DAC is more common in medium and high-precision digital-to-analog conversion applications.
  - Current output type DAC: Mainly outputs current signals. The current signal can be converted into a voltage signal through an external load resistor. This type of DAC has a high conversion speed and good linearity, and is often used in application scenarios that require fast conversion and high precision.
- Main Characteristics
  - Resolution: Similar to the analog-to-digital converter, the resolution of the digital-to-analog converter is also expressed in bits. It determines the fineness of the analog signal that can be output. A high-resolution DAC can output a more accurate analog signal and more accurately restore the analog content represented by the digital signal.
  - Conversion speed: Measure the number of times digital-to-analog conversion can be completed per unit time. For some applications that require real-time output of analog signals (such as audio playback, video display, etc.), a DAC with a higher conversion speed is required.
  - Linearity: Reflects the degree of linear relationship between the analog signal output by the DAC and the input digital signal. Good linearity can ensure that the analog signal can change accurately according to the digital signal and avoid signal distortion.
- Application Fields
  - Audio and video fields: In audio playback and video display devices, convert digital audio and video signals into analog signals to drive analog devices such as speakers and displays. For example, digital-to-analog converters play a key role in home theater systems, high-definition televisions and other devices.
  - Automation control field: Used to convert the digital control signal output by the digital control system into an analog control signal to drive analog actuators such as motors and valves to realize the control of industrial processes, robot movements, etc.
  - Instrumentation field: In some instruments that require analog signal output (such as signal generators), digital-to-analog converters are used to generate corresponding analog signals according to the digital parameters set by the user for testing and calibration purposes