Noise sources and input-referred noise
Noise sources in electronic devices and components refer to various origins of unwanted electrical signals, such as thermal noise, shot noise, and flicker noise, which can interfere with desired signals. Input-referred noise is the equivalent noise level that, if applied to the input of a device or circuit, would produce the observed output noise. This concept allows engineers to compare the noise performance of different devices by referencing all noise contributions back to the input.
Noise sources and input-referred noise
Noise sources in electronic devices and components refer to various origins of unwanted electrical signals, such as thermal noise, shot noise, and flicker noise, which can interfere with desired signals. Input-referred noise is the equivalent noise level that, if applied to the input of a device or circuit, would produce the observed output noise. This concept allows engineers to compare the noise performance of different devices by referencing all noise contributions back to the input.
💡 Key Takeaways
- Identify common noise sources in electronics (thermal, shot, and flicker noise) and how they influence input-referred noise.
- Define input-referred noise and learn how to express different noise sources as an equivalent input signal for comparison.
- Understand how noise is quantified using spectral density and bandwidth, and how temperature and bandwidth affect total noise.
- Explore practical ways to reduce input-referred noise through careful component selection, bandwidth control, layout, shielding, and filtering.
❓ Frequently Asked Questions
What is input-referred noise?
The equivalent noise at the input that would produce the observed output noise, used to compare noise performance across stages with a common reference.
What are the main noise sources in electronic circuits?
Thermal (Johnson–Nyquist) noise in resistors, shot noise in diodes/transistors, flicker (1/f) noise in active devices, and noise from power supplies/EMI; op-amp voltage and current noise are common contributors.
How is thermal noise for a resistor calculated?
RMS noise voltage = sqrt(4 k T R B); k is Boltzmann’s constant, T is temperature in kelvin, R is resistance, B is bandwidth in Hz.
How do you refer a noise source to the input?
Express the noise as an equivalent input quantity. For a voltage noise source, divide the output noise by the gain to get input noise. For a current noise source, multiply by the input impedance to obtain input-referred voltage. Combine all input-referred noises in RMS terms.