ANALYSIS OF NOISE UP-CONVERSION IN MICROWAVE FIELD-EFFECT TRANSISTOR OSCILLATORS

The conversion process of the low frequency noise into phase noise in field-effect transistors (FET) oscillators is investigated, First, an evaluation of the baseband noise contribution to the oscillator phase noise is provided from the analysis of the baseband noise and the freq uency noise spectra, A distinction is made within the different compon ents of the low frequency noise contributions to close-in carrier phas e noise, Next, the frequency noise of the oscillator circuit is analyz ed in terms of the FET's low frequency noise multiplied by the oscilla tor's pushing factor, Though this product usually provides a good eval uation of the phase noise, experimental results presented here show th e inaccuracy of this method at particular gate bias voltages where the pushing factor decreases to zero, To account for these observations, a new nonlinear FET model involving at least two noise sources distrib uted along the channel is proposed.