Tracking (up/down) digital-ramp ADC In practical data-converter design, how would you characterize the conversion speed of an up/down tracking (digital-ramp) ADC compared with other common architectures such as SAR or flash?

Introduction / Context:
The up/down tracking (digital-ramp) ADC is a classic converter architecture used when simplicity and low cost are more important than raw speed. Unlike flash or successive-approximation (SAR) converters, the tracking ADC adjusts its internal count step by step toward the input value, which has direct consequences for speed and response time.

Given Data / Assumptions:

• The device is a tracking (up/down) digital-ramp ADC.
• We are comparing its speed qualitatively against other architectures.
• No specific clock or resolution is provided; focus is on architectural behavior.

Concept / Approach:

A tracking ADC uses a counter and a DAC. The comparator determines if the DAC's output is above or below the analog input, then the counter increments or decrements by one step per clock until it matches the input. This “chasing” behavior means conversion time depends on how far the current code is from the new code, which can be many counts for large signal changes.

Step-by-Step Solution:

Verification / Alternative check:

Datasheet comparisons typically show tracking ADCs with bandwidth limited by the counter step rate; SAR devices at the same resolution complete conversions in a fixed, small number of cycles (for example, 8–16 cycles), confirming tracking ADCs are slower overall.

Why Other Options Are Wrong:

• 20 µs / 10 µs / 1 µs: These are arbitrary numbers and depend on clock, resolution, and design. The correct characterization is architectural, not a fixed time.

Common Pitfalls:

• Assuming speed is constant; tracking ADC time varies with input step size.
• Confusing tracking with SAR, which does not step linearly code by code.

Final Answer:

Relatively slow