Testing an A/D with a ramp — expected oscilloscope display When a proper ramp test is applied to an A/D converter (and its reconstructed output is observed), what should the oscilloscope display look like if the A/D is functioning correctly?

Introduction / Context:A common dynamic test for A/D converters feeds a linear ramp input and observes the digitized-then-reconstructed output. This reveals missing codes, DNL/INL errors, and monotonicity issues by visual inspection of the staircase shape on an oscilloscope.

Given Data / Assumptions:

• Input to A/D: linear voltage ramp spanning the converter range.
• Observation: either the A/D digital code decoded to a DAC or a scope plotting input vs. output.
• Ideal behavior: codes increment one by one with equal width steps.

Concept / Approach:If the converter is healthy, the output will change by exactly 1 LSB per code transition, producing a staircase with uniform step heights and widths. Nonuniform steps indicate DNL/INL issues; skipped steps indicate missing codes; reversals indicate nonmonotonic behavior.

Step-by-Step Solution:Apply ramp → A/D outputs successive codes.Convert codes back to analog (or XY display) → see stepwise increase.Ideal display is a uniform stairstep pattern.

Verification / Alternative check:Many application notes use the ramp test and show ideal staircases to illustrate linear, monotonic converters without missing codes.

Why Other Options Are Wrong:

• Lissajous pattern: Relates to two sinusoidal inputs, not A/D ramp testing.
• Straight line: Would imply continuous analog behavior, not quantized steps.
• Binary count display: That is a logic analyzer view, not an analog staircase on a scope.

Common Pitfalls:

• Mistaking a smoothed staircase due to bandwidth limits as ideal; verify sampling/hold effects.

Final Answer:A uniform stairstep pattern