What Is An ADC Converter?

What Is An ADC Converter?

An ADC converts continuous analogue input voltage into a series of binary numbers. These digital output codes are then used to represent the analogue input voltage by a control circuit.

ADCs are available as discrete designs sometimes constructed with hybrid packaging or monolithic designs implemented as ICs. Some of the major types include flash, pipelined and successive approximation-register designs.

Definition

ADC is a device that transforms the Analog signals in various forms like sound or electricity into the binary digital data which can be understood by microprocessors. Almost every measurable parameter in the environment is in analog form like temperature, light etc. To use these parameters with digital microprocessors and computers, they need to be converted into the corresponding binary form which can be read and understood by them. That is where an ADC comes in.

A typical ADC works by comparing the input analog signal with the reference voltage and then producing a digital value representing the difference between the two. The number of bits which represent this digital value decides the resolution of an ADC. This process is called sampling and the fidelity of the sampled signal can be determined by the Nyquist sampling theorem.

In order to achieve high accuracy and resolution, an ADC needs to be able to perform its function at a uniform rate. This is achieved by using a clock which sequences the internal operations of the ADC at a certain frequency. The clock can either be generated by the ADC itself or an external clock can be fed to it. The time taken for converting an input analog signal into a digital output value depends on the clock frequency. This is why choosing the right clock frequency is very important for an ADC.

Operation

The operation of a DAC can be divided into three blocks. The first block is a sample and hold which samples the input signal at an interval of time. The next hot plug controller block is a quantize which converts the continuous amplitude of the signal into discrete amplitude values. Finally the last block is an encoder which takes the digital value of the signal and converts it into binary code. This completes the conversion process.

There are many different types of ADCs. Two important specifications are the sample rate and bit resolution. The sample rate determines how fast the ADC can operate and the bit resolution determines the number of distinct values it can represent.

The simplest type of ADC is a single-slope ADC which uses an integrator to build up a reference voltage. A comparator then compares the integrator output with the set reference voltage and generates a counter value which represents the digital value of the input signal. This method is relatively simple but it requires a large comparator which limits its use.

Other types of ADCs use multiple comparator stages to increase the resolution. This reduces the amount of dimmable led driver time needed for each comparison and the noise generated by the comparator. Other techniques, such as dither noise and averaging, can also be used to improve the ADC’s performance.

Applications

An ADC converts a continuous-time, continuous-amplitude analog signal to a discrete-time, discrete-amplitude digital signal. This conversion introduces a small amount of quantization error. It also limits the maximum bandwidth of the input signal. A wide variety of ADC integrated circuits are available for a number of applications, including industrial measurement and control systems, communication systems, and sensors that provide data to sensory-based systems.

The resolution of an ADC is set by the number of bits used in its output code. The higher the resolution, the greater the accuracy of the digital output. The output code is generated by dividing the sampled analog input voltage by a reference voltage and then converting it to a binary value. Each bit corresponds to one of the possible output codes, and the resulting code is displayed on the converter’s output pins.

To produce a continuous digital output, an ADC must maintain the same input analog voltage for a fixed duration called the conversion time. This is achieved by using a sample-and-hold circuit, which stores the original analog input in a capacitor and then electronically disconnects the capacitor to allow the output of the comparator to take over. Most ADC integrated circuits incorporate this subsystem internally.

An ADC’s performance can be measured in several ways, but the most important parameters are its static (DC) and transfer curve characteristics. Dynamic testing focuses on the ADC’s ability to correctly interpret changes in signal amplitude and frequency, and to detect noise related issues.

Specifications

The ADC converts the conditioned analog input signal into an array of digital values. It is a key component of many data acquisition systems and sensor-based devices. The performance of the ADC can be characterized by a number of specifications including resolution, noise spectral density (NSD), speed, power consumption and cost.

The number of bits used to represent the output code is commonly referred to as converter resolution. A higher resolution ADC requires more comparators and voltage levels. The result is an increased overall complexity of the circuit.

Other important parameters include the LSB step size (the difference between an actual code transition point and a straight line drawn between the end points of the ADC transfer function). This metric is closely related to the ADC resolution and should always be quoted in terms of LSBs. Other specifications such as non-linearity, gain error, offset error and integral non-linearity, define how accurately the ADC converts an input signal into a digitized output.

Another specification is the common-mode rejection (CMR). This measures how well a differential input ADC rejects unwanted signals induced by other circuit components. This is especially important for high-speed applications where the power supply ripple can induce signals that cause distortion products to appear on the outputs. In addition, the CMR should be sufficient to limit interference from external devices such as high-power signals induced on the ground plane and RF leakage through mixers and RF filters.

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