Pericom Semiconductor Corporation

Craig M Taylor

Tony Yeung

Wing Faat Liu

Boris Drakhlis

David J Kenny

A crystal oscillator operates at the third overtone of the crystal's fundamental frequency. A value of a shunt resistor between the two phase-shift leg nodes is chosen so that the absolute value of the product gm&#xd7;(Xc)&#xd7;(Xc) is greater than the effective reactance of the crystal, where gm is the gain of the amplifier attached to the phase-shift legs, and Xcand Xcare the effective capacitive reactances of phase-shift legs at nodes Xand X. The third overtone is doubled by a multiplier and the final output filtered to remove the third overtone and select a frequency six times the fundamental frequency. A pair of Colpitts or Pierce amplifier half circuits is attached to the phase-shift leg nodes. The leg nodes can be capacitively isolated from Pierce-amplifier circuit nodes to improve start-up. Frequency doubling can be performed by summing currents from the two oscillator half circuits.

Crystal clock generator operating at third overtone of crystal's fundamental frequency

A printed-circuit board (PCB) module has co-planar solder pads on a bottom surface. The solder pads can be surface-mounted to pads on a main board, allowing the PCB module to be surface mounted without wire leads extending from the PCB module substrate. A cavity is formed between the solder pads on the bottom surface. The cavity is formed by milling away some of the thickness of a sacrificial insulator layer, which is the insulator layer under the solder-pad metal layer. The sacrificial insulator layer can be made thicker to allow for milling the cavity without milling into inner metal layers on the PCB module. After milling away much of the sacrificial insulator layer, stand-offs remain under the solder pads, providing a stand-off gap between the top of the cavity and the solder pads when soldered to the main board. The stand-off gap allows for cleaning under the PCB module.

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Pleasanton, CA, United States of America

Craig M Taylor