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What is Analog to Digital Converter?

by Sonali

An Analog to Digital converter is an electronic device which is used to convert analog signal into digital. This converter is available in the form of IC which can directly convert continuous signal into discrete form. There are three types of A/D converters which are explained below.

Dual Slope Analog to Digital Converter

An integrator is used in this type of converter which compares the generated voltage. The circuit consists of an Op-Amp with resistor and capacitor. There is a pre-defined reference voltage value Vref. The main work of this integrator circuit is to generate sawtooth waveform at its output. This waveform varies from value zero to Vref. The circuit also consists of a counter which starts to count on the application of input to the integrator. The counter counts from 0 to 2^n-1 where n is the number of bits of ADC.

As seen from the above circuit when the Vin i.e. input voltage becomes equal to the voltage of the waveform the counter takes the value of the analog input. The value of the input at that instance is recorded which is in digital form. The Dual slope converter is slow in speed. The cost is also in the medium range.

Flash A/D Converter’

This converter is most commonly used as it has good speed. The Flash A/D converter is also known as parallel ADC. The circuit consists of many comparators connected in series which compare the input voltage with the reference voltage. When the value of analog input voltage will be greater than the reference voltage the output of each comparator will be high. This output is fed to a priority encoder which produces binary code depending upon the higher order input. The cost of this converter is high.

Successive Approximation A/D Converter

This converter is fastest amongst all three discussed in this section. It is the latest type of IC used for analog to digital conversion. The digital logic used is very accurate as they converge the analog input to the closest value. The circuit components are SAR, comparators, latches and D/A converters.

Initially the SAR is having low value as it is reset first. There is a low to high transition due to which the MSB of SAR is set. The output produced is then fed to the D/A converter which in turn produces analog output of equivalent MSB. This output is then compared with analog input voltage Vin. When the output of a comparator is low MSB is cleared. If not, then the value of MSB is set to the next position. The process continues until all the bits are done. At last when Q0 is tried the successive approximation register produces output with proper data in parallel form.

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