Crystal oscillator driver with amplitude control

Details Crystal oscillator driver with amplitude control Crystal oscillator driver with amplitude control

1998-02-27

1999-12-07

Mis, David

Oscillators

Solid state active element oscillator

Transistors

331 74, 331108A, 331109, 331160, 331175, 331183, H03B 536

Patent

active

059990627

ABSTRACT:
A crystal oscillator drive circuit controls the maximum amplitude of the drive signal to a crystal by limiting the bias current of a gm cell which senses the oscillation amplitude of the crystal. The bias current is commutated by the gm cell responsive to the crystal oscillation. The commuted current is converted to a single-ended current by a current mirror. An output stage converts the current to an output voltage having a voltage swing that is determined by the resistance of a load resistor. The output voltage is then fed back to drive the crystal through a positive feedback path. The output voltage swing and the drive signal to the crystal are limited by the bias current of the gm cell. A fully complementary implementation of the drive circuit includes two complementary gm cells, two current mirrors, and an output stage having two load resistors. The complementary implementation is self biasing from the supply voltage and provides a symmetric topology that reduces crystal loading by cancelling the base currents in the gm cells. Unbalanced current mirrors having high current gain are utilized to provide a wide output voltage swing while reducing crystal loading by reducing the bias currents in the gm cells.

REFERENCES:
patent: 5770980 (1998-06-01), Barrett, Jr. et al.

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