Electronic Activity Dip Measurement

The frequency- or immittance-temperature anomalies occurring in quartz-crystal resonators are generically called activity dips. Because of their potentially disastrous effects on oscillator and filter performance, testing for their presence can represent a considerable addition to the manufacturing cost. An electronic method is described, in several variations, that is rapid, simple, and well adapted to microprocessor control. The electronic method obviates tedious and costly temperature runs. It makes use of the fact that the desired mode of vibration is shifted in frequency by a variable series capacitor, while interfering modes, that cause activity dips, are nearly unaffected.