An Analog to Digital Converter (ADC) is an integrated circuit that helps transform analog signals into a digital form. Put more simply: ADCs convert physical variables that are analog in nature like audio signals, temperature, pressure, and various others into digital signals for processing. They provide high conversion efficiency and necessitate less power than other converter options.
There are several types of Analog to Digital Converters, those of which are flash, pipelined, sigma delta, and successive approximation ADC types. To better understand the complexity of these devices, this blog will outline each of these ADCs, along with their applications, advantages, and disadvantages.
Also called parallel ADCs, flash ADCs are faster than their counterparts and find use in high-speed, large bandwidth applications. With this converter, the analog input is connected to all comparators so that the output is generated simultaneously. Meanwhile, the Reference Voltage (Vref) is provided to the comparator via an external source, and the digital output from the comparators serves as an input to the encoder, allowing it to convert the code from the comparator into binary code.
Pipelined ADCs are designed using two or more low resolution flash ADCs. This converter’s architecture is divided into stages that consist of a Sample and Hold circuit (S/H circuit) which samples the analog signal and holds the sampled value for a short period of time. This signal is then fed to the flash ADC to acquire the binary output. Each binary output is time-aligned or pipelined to the shift register and undergoes error detection and correction using digital error correction logic to obtain the final binary output.
Often referred to as oversampling converters, the architecture of sigma-delta converters is very simple. It consists of two main blocks: a sigma-delta modulator and a digital filter. A sigma-delta modulator has an integrator, comparator, and a single-bit DAC. A digital filter, on the other hand, is the output from the sigma-delta modulator that acts as the input to this block. As its name suggests, the digital filter filters data and converts it into binary code.
Successive Approximation ADCs
This type of ADC takes advantage of a successive approximation algorithm to convert analog input into digital binary code. Additionally, successive approximation ADCs consist of a comparator, successive approximation register (SAR), an S/H circuit, and a DAC.
ADCs find use in a wide range of applications including audio/video devices, cell phones, digital multimeters, PLCs, RADAR processing digital oscilloscopes, medical instrumentation and imaging, CMOS image sensors for mobile applications, and so much more.
Advantages & Disadvantages
Each ADC offers different advantages and disadvantages, some of which we will cover. For instance, flash ADCs are faster than their counterparts, but sigma-delta ADCs offer high resolution at low-cost. When you require high speed and reliability, depend on successive approximation ADCs. Pipelined ADCs offer a combination of the previous types’ features, with high resolutions at high speeds. In terms of disadvantages, circuity complexity increases with the use of comparators in flash ADCs, and they can also be expensive. Pipeline ADCs do not easily convert non-periodic signals and are sensitive to board layout. Lastly, successive approximation converters utilized for high resolution application will be slower in operation.
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