Q.With block diagram and waveform explain the working of the counting Analog to Digital converter.

A counting ADC converts an analog voltage to digital by letting a binary counter drive a DAC to build a rising staircase, and stopping the count when that staircase just reaches the analog input. …

[!TLDR]

A counting ADC uses a counter to drive a DAC that builds a rising staircase voltage; a comparator stops the counting the instant the staircase reaches the analog input, and the stopped count is the digital output.

Purpose: An analog-to-digital converter (ADC) converts an analog input (for example the output of a thermocouple representing a temperature difference) into a digital output that can be displayed.

Block diagram: The counting ADC consists of four blocks — a comparator, a binary counter, a DAC, and an AND gate. The clock feeds one input of the AND gate; the gate output drives the binary counter; the counter's binary output is the digital output and also feeds the DAC; the DAC output $V_O$ is compared with the analog input $V_A$ by the comparator, whose output controls (gates) the AND gate. A 'clear' line resets the counter.

Working:

1. The clear pulse resets the counter to zero count.
2. The counter then counts the clock pulses that pass through the AND gate.
3. The counter's binary output drives the DAC, whose output is a staircase waveform $V_O$ that rises one step per clock pulse.
4. The comparator continuously compares this staircase $V_O$ with the analog input $V_A$:
   • While $V_A > V_O$, the comparator output is high, which keeps the AND gate open, so clock pulses continue to reach the counter and the staircase keeps rising.
   • When the staircase $V_O$ just exceeds $V_A$, the comparator output goes low, disabling the AND gate; no more clock pulses reach the counter and the count stops (with $V_A \approx V_O$).
5. The value now held in the counter is the digital equivalent of the analog input voltage. …