Phase noise measurements on vibrating crystal filters

It is shown that bulk acoustic wave and surface acoustic wave crystal filters may induce phase modulation during mechanical vibration. The resulting phase modulation which occurs when the resonator is used in a filter is reviewed in terms of an effective acceleration sensitivity vector for the filter. The degradation in spectral purity is expressed as a function of this sensitivity. The phase shift through the filter is then quantified in terms of the acceleration sensitivity and the filter group delay. By considering typical values of acceleration sensitivity for bulk-wave resonators, estimates of the phase noise induced by the filter are made. Measurement results are presented for phase noise degradation in sine and random vibration. Measured results on a 5 MHz signal passed through a crystal filter show an increase in phase noise of greater than 20 dB in random vibration over static values. A degradation in Allan variance is also discussed