DAC verification – practical method for testing a digital-to-analog converter What is the basic, effective approach to test a D/A converter over its operating range?
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Aapply a sequence of binary codes covering the full range of input values to the circuit input while observing the output on an oscilloscope. The output should consist of a linear stairstep ramp.
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Bsingle-step the device through its full input range while checking the output with a DMM.
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Ccheck the output with zero input and then full input. The output of the converter should extend from zero to its maximum value. If so, then everything in between can be assumed to be operating properly.
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Dapply the correct input to the analog terminal and then check to see if the proper binary code exists on the digital inputs.
Answer
Correct Answer: apply a sequence of binary codes covering the full range of input values to the circuit input while observing the output on an oscilloscope. The output should consist of a linear stairstep ramp.
Explanation
Introduction / Context:Testing DACs involves verifying monotonicity, resolution, and linearity. A practical bench method examines the converter's response to all digital input codes and inspects the analog output for expected behavior.
Given Data / Assumptions:
- D/A converter under test; output can be observed on an oscilloscope or precision DMM.
- Full digital input code range is available.
- We want a quick but thorough functional check.
Concept / Approach:Feeding the DAC a count sequence from 0 to full scale and plotting output versus time should yield a monotonic staircase that approximates a straight ramp after filtering. This reveals missing codes, nonlinearity, glitches, and monotonicity violations. Spot checks at only two points (zero and full scale) do not validate intermediate behavior.
Step-by-Step Solution:
Drive DAC inputs with an up-counting binary counter through all codes.Observe output: a staircase rising in equal steps (LSB size).Assess linearity by comparing the staircase to a straight line; look for missing steps or reversals.Verification / Alternative check:Alternatively, capture pairs (digital code, analog output) and compute INL/DNL numerically; the oscilloscope method is a fast qualitative equivalent.
Why Other Options Are Wrong:
- Single-step with DMM: Better than two points, but too slow and still easy to miss dynamic issues/glitches.
- Zero and full scale only: Does not detect missing codes or nonlinearity.
- Applying analog to DAC and checking digital: Reversed; that describes ADC testing.
Common Pitfalls:
- Using insufficient settling time per code and misinterpreting transient glitches as errors.
- Failing to ensure reference stability and low-noise grounding during measurement.
Final Answer:apply a sequence of binary codes covering the full range … linear stairstep ramp