Flicker Noise
Understanding Flicker Noise
Flicker noise is particularly important in RF because it converts to close-in phase noise in oscillators. The 1/f noise of the active device modulates the oscillation frequency, creating a 1/f^3 phase noise region close to the carrier. Lower flicker noise results in better close-in phase noise performance.
Flicker Noise by Technology
- GaAs pHEMT: Corner frequency 1-10 MHz. Moderate 1/f noise.
- SiGe HBT: Corner frequency 1-100 kHz. Excellent 1/f noise (bipolar advantage).
- GaN HEMT: Corner frequency 1-100 MHz. Higher 1/f due to material defects.
- InP HEMT: Corner frequency 100 kHz - 10 MHz.
- Silicon MOSFET: Corner frequency 1 kHz - 10 MHz. Varies with process.
Impact on Phase Noise
In oscillators, Leeson's model shows that the 1/f noise corner of the active device creates a 1/f^3 phase noise region. Beyond the corner, phase noise follows a 1/f^2 slope (from white noise). This is why SiGe oscillators often have better close-in phase noise than GaAs oscillators.
Frequently Asked Questions
What is flicker noise?
Flicker noise is low-frequency noise with power spectral density proportional to 1/f. It is caused by charge carrier trapping at semiconductor defects. It is the dominant noise mechanism at low frequencies and converts to close-in phase noise in oscillators.
Why does flicker noise matter for oscillators?
Flicker noise in the oscillator's active device modulates the oscillation frequency, creating a 1/f^3 close-in phase noise region. Lower device flicker noise directly improves oscillator phase noise performance at small frequency offsets from the carrier.
Which semiconductor technology has the lowest flicker noise?
SiGe HBTs have the lowest flicker noise corner frequency (1-100 kHz) due to the bipolar junction's lower trap density. GaAs HEMTs are moderate (1-10 MHz). GaN HEMTs have the highest (1-100 MHz) due to material quality challenges.