O. Llopis et al., PHASE NOISE IN CRYOGENIC MICROWAVE HEMT AND MESFET OSCILLATORS, IEEE transactions on microwave theory and techniques, 41(3), 1993, pp. 369-374
This paper addresses the influence of cooling on the phase noise of HE
MT and MESFET oscillators. The initial measurements of the device dc c
haracteristics and low frequency noise (0.1 kHz-100 kHz) under cooling
give indications on the suitability of a given device for use in low
phase noise cooled oscillators. Cooled pseudomorphic AlGaAs/GaInAs/GaA
s HEMT's (PHEMT's) turn out to be particularly well-suited as they are
free of collapse and they are free of g-r noise in the frequency rang
e of interest. We report on 4 GHz oscillators operated at 110 K and fe
aturing a phase noise below -100 dBc/Hz at 10 kHz from the carrier in
spite of a very modest loaded Q (160). It is suggested that high tempe
rature superconductor resonators could greatly enhance the spectral pu
rity of PHEMT's oscillators.