Solution: Noise Sources and Noise Reduction Techniques

Noise

Noise is an unwanted electrical signal that interferes with the desired measurement signal and reduces measurement accuracy.

Major Noise Sources

1. Thermal Noise

Produced by random motion of charge carriers in resistive components. Its noise power increases with temperature and bandwidth.

2. Shot Noise

Caused by the random arrival of charge carriers, especially in semiconductor devices and junctions.

3. Flicker Noise

Also called 1/f noise. It becomes important at low frequencies and is associated with electronic devices and materials.

4. Electromagnetic Interference (EMI)

Motors, transformers, switching circuits, mobile/radio transmitters and power lines can induce unwanted signals.

5. Ground Loops

Different ground potentials can create unwanted circulating currents and 50/60 Hz interference.

6. Crosstalk

A signal from one channel can couple into another through electrical or electromagnetic coupling.

7. Quantization Noise

Introduced when an analog value is represented by a finite number of ADC levels.

Noise Reduction Techniques

1. Shielding

Use shielded cables and conductive enclosures to reduce electromagnetic pickup.

2. Proper Grounding

Use a carefully designed grounding scheme and avoid unnecessary ground loops.

3. Twisted-Pair Cables

Twisting reduces pickup from external electromagnetic fields, especially for differential signals.

4. Differential Measurement

Measure the voltage difference between two signal terminals rather than relying on a common ground reference. This improves rejection of common-mode interference.

5. Filtering

Use low-pass, high-pass, band-pass or notch filters according to the measurement bandwidth.

6. Isolation

Isolation amplifiers, transformers or digital isolators can break unwanted electrical paths.

7. Short and Proper Wiring

Keep sensitive signal wires short, route them away from high-power cables and separate analog and noisy digital wiring.

8. Averaging and Digital Filtering

Repeated measurements can be averaged, and digital filters can reduce random noise after acquisition.

Conclusion

Noise reduction requires a combination of shielding, grounding, differential measurement, filtering, isolation and proper wiring. The best technique depends on the source and frequency of the interference.