Effects of gain compression, bias conditions, and temperature on the flicker phase noise of an 8.5 GHz GaAs MESFET amplifier

The authors have measured the phase noise of an 8.5-GHz GaAs MESFET amplifier at temperatures from 1.7 K to 300 K for input powers from -30 dBm to well past the 1-dB gain compression point and for sideband frequencies from 0.1 Hz to 25 kHz. The observed flicker phase noise was independent of input power, even at levels producing 4 dB of gain compression, and also changed very little with bias conditions. The intrinsic phase noise at temperatures below 2.17 K was slightly higher than that observed at room temperature. However, no sign of the dramatic increase in flicker phase noise at low temperatures recently reported at 9.7 GHz was observed. Based on this data, it is predicted that a cryogenic loop oscillator built from such an amplifier should have exceptionally good short-term frequency stability.>