Improved correlation between quartz crystal manufacturing and oscillator requirements

Specification of quartz crystal parameters for oscillator applications is an inexact science. In many cases, the measured crystal performance is determined by the vendor to meet or exceed the stated specifications. Yet, the crystal will not perform as expected in the oscillator. This is especially true in center frequency and in tuning range. During the nearly 40 years that Hewlett-Packard, now Agilent Technologies, produced quartz crystals, we devoted significant engineering resources to continually increase yield throughout the entire process. Part of that work was centered on the need to have repeatable center frequency with a tolerance of /spl plusmn/0.3 ppm and a mechanical tuning range that was always at least /spl plusmn/1 ppm for a 10 MHz, 3/sup rd/ overtone, SC-cut. Continuing oscillator development eventually led to an EFC range requirement that was always at least /spl plusmn/0.5 ppm.. Key to achieving the requirements with high yield are several factors. First, the final frequency plating is done using an S-parameter network analyzer with adequate software to measure crystal performance at its future operating points. Second is an intimate knowledge of the oscillator performance, especially at the end points of both the mechanical and electrical tuning ranges. Third is a willingness to perturb the crystal parameters to meet continuing changes in the oscillator electronics.