Reduction of quartz crystal oscillator flicker-of-frequency and white phase noise (floor) levels and acceleration sensitivity via use of multiple resonators

Through the use of N series-connected, quartz crystal resonators in an oscillator circuit, a 10log_N reduction in both flicker-of-frequency noise and white phase noise (floor) levels is possible. The reduction in flicker noise occurs as a result of the uncorrelated short-term frequency instability in each of the resonators, and the reduction in noise floor level is a result of the increase in net, allowable crystal drive level. This technique has been used in 40-MHz, 80-MHz, 100-MHz, AT, BT, and SC-cut crystal oscillators using low flicker-of-phase noise, modular amplifier sustaining stages, and four series-connected crystals. The use of four crystals allows crystal mounting in fixed, relative orientations so that, if the direction and amplitude of the acceleration sensitivity of each individual crystal vector are identical, exact cancellation occurs for all directions. In practice, unit-to-unit sensitivity vector amplitude and direction are nonidentical. However, even under these circumstances, a four- to five-fold reduction in acceleration sensitivities has been demonstrated