The resistor net and comparators provide an input to the combinational logic circuit, so the conversion time is just the propagation delay through the network - it is not limited by the clock rate or some convergence sequence. Illustrated is a 3-bit flash ADC with resolution 1 volt (after Tocci). A comparator and a DAC are used in the process. The successive approximation ADC is much faster than the digital ramp ADC because it uses digital logic to converge on the value closest to the input voltage. Illustration of 4-bit SAC with 1 volt step size (after Tocci, Digital Systems). The transition of the comparator stops the binary counter, which at that point holds the digital value corresponding to the analog voltage. Since the output of the DAC is increasing with the counter, it will trigger the comparator at some point when its voltage exceeds the analog input. The output of the DAC is applied to the other terminal of the comparator. A common way to do that is to apply the analog voltage to one terminal of a comparator and trigger a binary counter which drives a DAC. HyperPhysics***** Electricity and magnetismĬonversion from analog to digital form inherently involves comparator action where the value of the analog voltage at some point in time is compared with some standard. It is typical for an ADC to use a digital-to-analog converter ( DAC) to determine one of the inputs to the comparator. The basic principle of operation is to use the comparator principle to determine whether or not to turn on a particular bit of the binary number output. This is a sample of the large number of analog-to-digital conversion methods. Analog to Digital Conversion Analog-to-Digital Conversion
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