How do you design and test electronic circuits for noise immunity and robustness?

1 Noise sources

Noise sources can be classified into two categories: intrinsic and extrinsic. Intrinsic noise sources are inherent to the physical components and processes of the circuit, such as thermal noise, shot noise, flicker noise, and burst noise. Extrinsic noise sources are external to the circuit, such as electromagnetic interference, power supply noise, and environmental noise. Some noise sources are deterministic, meaning they have a predictable pattern or frequency, while others are random, meaning they have a variable or unpredictable nature.

2 Noise types

Noise types can be classified into two categories: common-mode and differential-mode. Common-mode noise is the same for both the signal and the reference, and it affects the signal level or offset. Differential-mode noise is the difference between the signal and the reference, and it affects the signal quality or shape. For example, a common-mode noise can cause a DC shift or a low-frequency drift in the signal, while a differential-mode noise can cause a distortion or a high-frequency fluctuation in the signal.

3 Noise immunity

Noise immunity is the ability of a circuit to resist or reject noise, and to maintain its functionality and performance under noisy conditions. Noise immunity depends on several factors, such as the signal-to-noise ratio, the bandwidth, the filtering, the shielding, the grounding, and the layout of the circuit. To improve noise immunity, you can use techniques such as differential signaling, balanced lines, twisted pairs, coaxial cables, ferrite beads, decoupling capacitors, and low-pass filters.

4 Noise robustness

Noise robustness is the ability of a circuit to tolerate or adapt to noise, and to recover its functionality and performance after a noisy event. Noise robustness depends on several factors, such as the error detection, the error correction, the feedback, the redundancy, and the fault tolerance of the circuit. To improve noise robustness, you can use techniques such as parity bits, checksums, cyclic redundancy codes, error correction codes, retransmission, acknowledgment, watchdog timers, and fail-safe modes.

5 Noise measurement

Noise measurement is the process of quantifying and characterizing the noise in a circuit, and evaluating its impact on the signal. Noise measurement can be done using various instruments, such as oscilloscopes, spectrum analyzers, noise generators, noise meters, and noise figure meters. Some common noise parameters that can be measured are the noise voltage, the noise current, the noise power, the noise density, the noise factor, the noise figure, and the signal-to-noise ratio.

6 Noise simulation

Noise simulation is the process of modeling and analyzing the noise in a circuit, and predicting its behavior and performance under noisy conditions. Noise simulation can be done using various software tools, such as SPICE, MATLAB, LTspice, and Cadence. Some common noise models that can be used are the white noise model, the pink noise model, the Gaussian noise model, and the Poisson noise model. Noise simulation can help you to optimize your circuit design for noise immunity and robustness, and to verify your noise measurement results.