ADC architecture identification: Which converter uses an up/down counter and associated circuitry to “track” or follow changes in the analog input signal over time?
Digital Electronics
Digital Signal Processing
Difficulty: Easy
Choose an option
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Asingle-slope ramp converter
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Bdual-slope ramp converter
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Csuccessive-approximation converter
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Dtracking converter
Answer
Correct Answer: tracking converter
Explanation
Introduction / Context: Various ADC structures trade off speed, complexity, and noise immunity. A tracking (or servo) ADC maintains a running estimate of the input and adjusts up or down as the input changes, making it intuitive for slowly varying signals.
Given Data / Assumptions:
- The description mentions an up/down counter following the input.
- Tracking ADCs use a DAC and comparator in a feedback loop.
- Other architectures exhibit different, non-tracking behaviors.
Concept / Approach: In a tracking ADC, the digital output drives a DAC. The comparator compares the DAC output to the input. If the input is larger, the counter counts up; if smaller, it counts down. Thus, the code “tracks” the analog signal with a rate limited by clock and step size.
Step-by-Step Solution:
Initialize counter to a starting code.Compare DAC(code) to analog input.If input > DAC, increment; if input < DAC, decrement.Repeat continuously; digital code follows the input trajectory.Verification / Alternative check:
Block diagrams in textbooks show the counter–DAC–comparator feedback loop characteristic of tracking ADCs.Why Other Options Are Wrong:
single-slope ramp: Uses a counter with a fixed ramp and timing measurement, not continuous tracking.dual-slope: Integrating technique for high noise rejection; no up/down tracking loop.successive-approximation: Bit-by-bit binary search per sample, not continuous up/down following.Common Pitfalls:
Assuming tracking ADCs are best for all cases; they can be slower to respond to abrupt changes than SAR or flash.Ignoring the steady-state limit cycle behavior around a changing input.Final Answer:
tracking converter