Treatment of Flicker Noise in Oscillators and Methods of Its Suppression

This paper deals with impact to oscillator phase noise from flicker noise in elements of oscillator circuitry and aims to estimate an available level of close-in phase noise in perspective oscillator schemes and discuss some ways of phase noise improvement. The treatment exploits an idea that any structural element of an oscillator, e. g., any stage of a cascaded sustaining amplifier operates, besides its main function, like a variable phase shifter guided with noise which modulates an induced phase shift. This approach explains the PM noise dependence on power gain in bipolar transistor amplifiers and helps to optimize a number of stages. The paper undeceives a widely distributed opinion that an amplifier design technique that achieves highly linear operation certainly lowers oscillator phase noise. As estimated, an X-band room temperature bridge-type oscillator can reach as low phase noise as -(140...145) dBc/Hz at 1 kHz offset. The theoretical limit of phase noise in optimized oscillators equipped with an automatic frequency control is approximately -165 dBc/Hz in the same conditions