A SAWR oscillator vibration sensitivity and phase noise reduction technique using multiple resonators and RF outputs

Abstract

A technique previously described by the author for reduction of quartz crystal oscillator vibration sensitivity and phase noise has been modified and applied to the design of a UHF, SAWR oscillator. Use of four SAW resonators mounted in an in-plane orientation provides 3-axis vibration sensitivity cancellation. Because of variations in individual SAWR vibration sensitivity vector magnitude and direction, the cancellation is non-exact. However, a 14:1 reduction in vibration sensitivity has been achieved using resonators having fairly uniform individual sensitivities in the range 44/spl times/10/sup -9/ to 55/spl times/10/sup -9/ per g. The novel oscillator loop circuitry consists of cascaded stages of SAWR/modular amplifier/power divider combinations, providing multiple, per-stage RF output signals whose noise phase floors are uncorrelated as a result of individual SAW resonator frequency selectivity. Thus, output signal amplitude (power combiner) or frequency (mixer) summation of M oscillator outputs yields a 10logM noise floor improvement. A minimum, 10logN improvement in flicker-of-frequency noise is obtained via use of N resonators due to the uncorrelated nature of the individual resonator frequency instabilities and N times increase in oscillator loop group delay. Phase noise floor levels on the order of -185 dBc/Hz and flicker-of-frequency noise levels given by f(100 Hz)=-124 dBc/Hz have been demonstrated in an oscillator using 320 MHz SAW resonators manufactured by SAWTEK, Inc., using the technique (with M=N=4), which is also applicable to oscillators incorporating other types of resonators.