Single-slope (ramp) A/D converter operation Which statement best describes the basic operating principle of a single-slope A/D converter?
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AThe input voltage sets a VCO frequency that is then measured as a proxy for voltage.
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BA ramp generator enables a counter through a comparator; when the ramp equals the input, the counter is latched and reset. The count is proportional to the input.
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CAn integrating capacitor is charged by the input until it equals a separate ramp; the ramp is then read out as the result.
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DAny of the above could be correct depending on converter type.
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EThe comparator outputs a PWM signal whose duty cycle is the result.
Answer
Correct Answer: A ramp generator enables a counter through a comparator; when the ramp equals the input, the counter is latched and reset. The count is proportional to the input.
Explanation
Introduction / Context:Single-slope (ramp) A/D converters are classic measurement circuits in panel meters and simple data acquisition. They trade speed and noise rejection for simplicity.
Given Data / Assumptions:
- The converter generates a known, linear ramp (constant V/second).
- A comparator detects when the ramp crosses the unknown input voltage.
- A digital counter measures ramp time from start to crossing.
Concept / Approach:If the ramp slope is constant, the time to reach the unknown input is proportional to the input magnitude. Counting clock pulses during this interval yields a digital number proportional to the analog input.
Step-by-Step Solution:Start ramp at a known time and zero level.Enable counter simultaneously and feed clock pulses.Comparator trips when ramp voltage equals input voltage.Latch the count, reset ramp and counter for the next measurement.
Verification / Alternative check:Contrast with dual-slope ADCs (integrate input for a fixed time, then de-integrate with a reference) and SAR ADCs (binary search). The single-slope clearly matches the ramp-and-count description.
Why Other Options Are Wrong:VCO frequency measurement (option A) describes a voltage-to-frequency converter based ADC, not single-slope.Integrating to match a ramp (option C) confuses integrator methods with dual-slope behavior.“Any of the above” (option D) is too broad; specific architectures differ.PWM duty cycle (option E) describes a different modulation-based scheme.
Common Pitfalls:Assuming single-slope provides good noise rejection like dual-slope; it does not, since noise directly perturbs the trip timing.
Final Answer:A ramp generator enables a counter through a comparator; when the ramp equals the input, the counter is latched and reset. The count is proportional to the input.