Phase Noise of Various Frequency Doublers

Previous studies of phase noise contributed by amplifiers and frequency multipliers have indicated the existence of a so-called "flicker of phase noise law of p-n junction." Contradictions of this law were obtained using low-noise transistors in frequency doublers. Schottky barrier diode and vacuum-tube multipliers were compared to the p-n junction devices. The tube doublers exhibited an anomaly, since their phase noise did not change with the application of negative feedback, indicating the possibility that the tubes themselves may be much better than the observed noise. The noise of the transistor doublers was progressively reduced by application of increasing amounts of negative feedback until a lower limit was reached. The noise then remained constant in spite of further increases in the amount of negative feedback. Measurements were obtained on all doublers from 2 Hz to 5 kHz with extrapolation to 1 Hz. During the investigation, a low-flicker-noise low-drift dc preamplifier was developed.