Test and Measurement Techniques

Overview

Reliable measurement is the backbone of good design. This chapter describes how to set up reproducible tests using oscilloscopes, spectrum analysers, probes, proper grounding, and how to document results for debugging and verification.

Prerequisites

• Familiarity with basic bench instruments (multimeter, oscilloscope)

Learning objectives

• Choose appropriate probes and measurement setups to avoid loading and artefacts
• Use spectrum analysers and scopes to characterise noise, jitter, and spectral content
• Create repeatable test procedures and record results for verification

Tools & materials

• Oscilloscope, spectrum analyser, probes, near-field probes (optional), calibrated sources

Hands-On Mini Task

1. Create a simple measurement checklist for verifying a regulator: setup, probes, expected ranges, and acceptance criteria.
2. Measure output ripple and spectrum, and document findings with screenshots and a short report.

Expected result: clear, repeatable measurements and a basic report that can be used to compare design revisions.

Measurement theory and best practices

• Always consider the measurement bandwidth: scope bandwidth, sampling rate, and probe response define what you can trust in a measurement.
• Probe loading: active probes reduce loading for high-impedance or high-frequency nodes; use short ground connections to avoid loops.

Setting up repeatable tests

• Create a checklist: instrument settings, probe types, grounding points, ambient conditions, and steps to reproduce a test.
• Capture metadata with each screenshot: sample rate, probe attenuation, and date/time.

Advanced measurement techniques

• Use FFT and windowing properly for spectral measurements; record sample length and window type when reporting SNR or THD.
• Near-field probing helps localise radiating hotspots for EMI debugging.

Worked example — regulator ripple and spectrum

1. Place scope probe at regulator output with 10× probe, short ground spring. Set scope to 50 MHz bandwidth limit and capture waveform.
2. Use FFT with a Hanning window, record the RMS ripple and spectral peaks; compare pre- and post-decoupling changes.

Troubleshooting measurement artefacts

• If you see unexpected spikes, verify the probe ground isn't creating a loop; try a differential probe or a ground spring.
• If measurements vary between runs, stabilise the DUT (warm-up), and ensure consistent load conditions.

Further reading and resources

• Tektronix/Keysight application notes on probing and spectrum analysis.
• Manufacturer ANs for specific probe usage and measurement accuracy.

Navigation

• Previous: Thermal Management and Reliability
• Next: RF Basics