Counter-ramp ADC architecture If the same analog signal is digitized to 8-bit resolution using a counter-ramp (integrating) ADC, how many comparator circuits are required in the converter hardware?

Introduction / Context:
Different ADC architectures trade off speed, complexity, and hardware cost. The counter-ramp (or digital ramp) ADC uses a simple structure compared with flash ADCs. Understanding how many comparators are needed helps in estimating silicon area, power, and cost.

Given Data / Assumptions:

• Resolution = 8 bits.
• Architecture = counter-ramp (digital ramp) ADC.
• Reference DAC and a single comparator are typical in this topology.

Concept / Approach:

In a counter-ramp ADC, a binary counter drives a DAC to generate a rising staircase. A single comparator compares the DAC output with the analog input. When the DAC output equals or just exceeds the input, the comparator stops the counter, and the counter value is the digital result. Unlike flash ADCs, which require 2^n − 1 comparators, counter-ramp ADCs require only one comparator regardless of resolution.

Step-by-Step Solution:

Verification / Alternative check:

Compare with flash ADC: for 8 bits, flash needs 2^8 − 1 = 255 comparators. Successive-approximation ADCs also use one comparator. The single-comparator result aligns with established architectures.

Why Other Options Are Wrong:

• 8, 127, 255: These reflect multi-comparator designs like flash ADC; not applicable to counter-ramp.

Common Pitfalls:

• Confusing counter-ramp with flash or SAR and assuming comparator count scales with 2^n.

Final Answer:

1