PURPOSE: To eliminate defective oscillators earlier, by finding out the relation between a frequency drift and a usage time and expecting the state after a long time.
CONSTITUTION: Taking a difference of oscillated frequency of an oscillator from the design value as Y axis and the power of 10 like 1, 10, 100, 1,000 for the lapse of usage time, e.g., number of days as X axis, a frequency drift is a straight line passing through the origin. After the start of an oscillator Fs2 to be tested, the amount of drift is detected at a phase comparator PD in comparison with a standard oscillator Fs1. For example, a voltage of the phase comparator PD is greatly changed with a difference of frequency 1Hz, and the change is counted at a counter CNT1 after frequency division at a frequency divider 1/L via a differentiation circuit. The count value of the counter CNT1 is read when an output signal from a counter CNT2 is present, and the value is compared with α, 2α..., which is a value set as the standard drift. If the drift is α or more, the value is taken care and it is inspected if the value is 2α or more at 100 days, and if it exceeds 2α, the oscillator is taken as a defective good.
TANIGUCHI YOSHIHIKO
SUZUKI HAYASHI
