Short-Term Frequency Stability of Relaxation Crystal Oscillators

Due to the need for stable frequency rectangular wave signals, various relaxation quartz crystal oscillators were designed. Therefore it is of interest to have data on their short-term frequency stability. The generally accepted definitions of measures for short-term frequency stability and measurement procedures are reviewed in this paper. Measurement results for the short-term frequency stability of quartz crystal multivibrators in time and frequency domains show a high spectral purity of the multivibrator output signal. The single-sideband-to-carrier phase noise has values lower than -90 and -120 dB on the offset frequencies of 1 and 10 Hz, respectively. The white phase noise is about -160 dB. The power law spectral density model of fractional frequency fluctuations for the quartz multivibrators is established and a discussion on the noise sources is given.