THE ROLE OF BASEBAND NOISE AND ITS UP-CONVERSION IN HBT OSCILLATOR PHASE NOISE

The phase noise spectral density pound(f(m))) of an 11.02-GHz heteroju nction bipolar transistor (HBT) dielectric resonator oscillator (DRO) has been investigated in terms of the HBT's low frequency noise and th e oscillator's upconversion coefficient. Experimental studies have bee n used for this purpose and the measured pound(f(m)) ranged from -89 d Bc/Hz to -101 dBc/Hz at a 10-kHz offset frequency (best phase noise sp ectral density performance was -124 dBcM/Hz at 100 kHz). It was shown that, in most test cases, pound(f(m)) can be described by the upconver sion of the HBT's baseband noise, As a result the frequency dependence , of pound(f(m)), is dictated by the low frequency noise spectrum rath er than the upconversion itself, Deviation from pure 1/f frequency dep endence found for the HBT's baseband noise at frequencies above 100 Hz resulted in d pound(f(m))/d(f(m)) deviating from about -30-dB/decade rate. Reduced oscillator phase noise at high collector current is attr ibuted to reduced upconversion in the oscillator.