Noise Reduction Tips for Oscilloscope Measurements
Even a high-performance oscilloscope can show noise on the waveform if the measurement setup is not optimized. This guide explains simple, practical techniques to reduce noise and achieve cleaner, more reliable measurements.
1. What Causes Noise in Oscilloscope Measurements?
Oscilloscope noise typically comes from grounding issues, environmental interference, and incorrect oscilloscope settings. The table below summarizes the most common noise sources and their impact.
| Noise Source | Description | Impact Level |
|---|---|---|
| Long Ground Lead | Forms a loop that acts like an antenna and picks up AC and RF noise. | High |
| EMI (Lab Environment) | Noise from switching power supplies, laptops, motors, lighting, etc. | Medium |
| Oscilloscope Bandwidth | High bandwidth shows more high-frequency noise than required. | Medium |
| Probe Placement | Probing on long wires or poor PCB contact increases interference pickup. | High |
| Vertical Scale Sensitivity | Very small mV/div settings amplify even tiny noise components. | Low |
2. Use the Shortest Possible Ground Connection
A long ground clip is the number one cause of unnecessary noise. Shortening the ground connection significantly reduces ground-loop interference.
Recommended practice:
- Use the short ground spring or blade adapter included with your UNI-T probes.
- Always connect ground close to the measurement point.
- Avoid test wires or flying leads longer than necessary.
3. Optimize Probe Placement and PCB Contact
Incorrect probing increases noise dramatically. Probing directly on high-quality PCB pads ensures stable and clean measurements.
Probe placement tips:
- Always probe directly on test pads or short PCB traces.
- Avoid probing over long wires—they act as antennas.
- Use a differential probe if measuring differential signals.
4. Use Bandwidth Limit and Averaging
UNI-T oscilloscopes include digital tools that clean up your measurement without affecting the actual signal.
Useful features:
- Bandwidth Limit (20MHz) – removes unnecessary high-frequency noise.
- Averaging Mode – averages multiple acquisitions to smooth random noise.
- Math Filters – apply low-pass or high-pass filtering to isolate waveform details.
5. Adjust Vertical Scale and Coupling
Incorrect vertical settings can make the waveform look noisier than it is.
- Use a vertical scale that fits the entire waveform.
- Use AC coupling when measuring ripple on a DC line.
- Avoid unnecessarily sensitive mV/div settings.
6. Reduce EMI and Ground Loops
Environmental noise can significantly affect sensitive measurements.
Reduce EMI:
- Move the scope away from laptop chargers, transformers, or motors.
- Use shielded cables when possible.
- Avoid placing the DUT near switching power supplies.
Prevent ground loops:
- Ensure all instruments share a common grounding point.
- Never disconnect or bypass protective earth from the oscilloscope.
Quick Noise Reduction Checklist
- Use short ground spring / blade.
- Probe directly on PCB pads.
- Enable 20MHz bandwidth limit.
- Use averaging for repetitive signals.
- Set proper vertical scale and coupling.
- Minimize EMI & avoid ground loops.
