Low Frequency Noise Quartz Crystal Oscillator

For years, engineers and scientists have been plagued by an extremely undesirable property of the quartz crystal unit-its significant frequency shift as a function of drive level for drive levels in excess of 10 to 100 μW. This fact was reported by Hammond [1]. As a result, all precision and moderate precision quartz oscillators have been operated at low drive in an effort to avoid the phenomena. The author has discovered, however, that this unique property of the quartz resonator can be effectively utilized in the design of the quartz oscillator with the result of substantial improvement in oscillator short-term frequency stability. Futhermore, since the crystal frequency-drive characteristic is repeatable, maintenance of moderately high crystal drive in the oscillator circuit will not result in long-term frequency instability in excess of that required for the majority of radar and communication systems [2].