What Are Noise and SNR?
1 min read
Quick answer
Noise is an unwanted, random signal mixed into the useful one. SNR (Signal-to-Noise Ratio) is the ratio of the useful signal to the noise, and it's the most important measure of signal quality.
What Is Noise?
Every real circuit has some noise. The problem is the size of the noise relative to the useful signal; noise on top of a weak signal can make it unreadable.
Noise Sources
| Source | Example |
|---|---|
| Thermal noise | Thermal motion in resistors |
| External interference (EMI) | Motors, switching, RF |
| Power line | Mains hum (50/60 Hz) |
| Ground loop | Poor GND layout |
Signal-to-Noise Ratio (SNR)
The higher the SNR, the cleaner the signal; it's usually given in decibels (dB). A high SNR means clear audio and accurate measurement.
Reducing Noise
Filtering, a good ground layout, shielding, short cables and amplifying the signal at its source all reduce noise. Applying gain late also amplifies the noise.
Common Mistakes
- Amplifying noise with the signal: boosting a weak signal later instead of at its source ruins the SNR.
- Neglecting the ground: a poor GND layout is the most common noise source.
- Skipping shielding: sensitive analog lines are exposed to external interference.
Frequently Asked Questions
Why does SNR matter?+
It shows how well the signal can be distinguished from the noise; it's the measure of quality and accuracy.
Can noise be eliminated completely?+
No; fundamental sources like thermal noise always exist, but they can be reduced.
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