To compare input and output signals simultaneously during troubleshooting (e.g., verify gain, phase, and distortion), which test instrument is most appropriate?

Introduction / Context:
Many diagnostics require observing two or more nodes at once—such as an amplifier’s input vs. output to assess gain and phase, or two related digital lines to examine timing relationships. The chosen instrument must display multiple traces concurrently with a shared time base.

Given Data / Assumptions:

• Need to visualize two or more signals at the same time.
• Accurate timing correlation is required (same horizontal sweep).
• Qualitative and quantitative comparisons (amplitude, delay) are desired.

Concept / Approach:
A multitrace (dual- or multi-channel) oscilloscope displays multiple signals stacked vertically but time-aligned horizontally. This allows direct, visual comparison of amplitude, phase shift, propagation delay, and distortion.

Step-by-Step Solution:
Connect probes to input and output nodes; select identical attenuation.Set time base and trigger on the input for stable display.Adjust vertical scales; measure gain (Vout/Vin) and phase/time shift.Use math functions if available (e.g., A–B) for further analysis.

Verification / Alternative check:
Frequency response can be corroborated using a network analyzer, but for quick, in-circuit comparisons, a multitrace oscilloscope remains the fastest approach.

Why Other Options Are Wrong:

• Single-channel oscilloscope: Cannot show both signals simultaneously with shared timing.
• Logic probe: Indicates logic levels but not analog shape or timing.
• Spectrum analyzer: Frequency-domain visualization; not time-domain comparison across nodes.

Common Pitfalls:

• Mismatched probe compensation skews waveform comparisons.
• Incorrect ground referencing can introduce ground loops or ringing.

Final Answer:
a multitrace oscilloscope