Crystal oscillator circuit for fast reliable start-up

Abstract

Abstract The present invention provides a circuit which facilitates fast and reliable start-up of an oscillator crystal without the amplification of undesirable frequencies of noise. A crystal is provided which is connected in parallel to an amplifying inverter having an input and an output. Grounded capacitors are connected respectively to the input and output of the inverter for stability. A first high resistance feedback path and a second low resistance feedback path are provided between the output of the inverter and the input of the inverter. A switch is also provided for selectively engaging or disengaging the low resistance feedback path with the inverter at preselected points in time. During operation of the circuit in the preferred manner, the switch engages the low resistance feedback path with the inverter to allow maximum charge build-up at the stabilizing capacitors upon turn-on of a supply voltage, thus quickly generating a large input voltage at the inverter. The voltage at the input of the inverter quickly becomes equal to the voltage at the output of the inverter, resulting in high gain. Thereafter, the switch disengages the low resistance path from the inverter, creating a voltage transition. The voltage transition results in high level noise which may quickly be amplified by the high gain inverter to generate maximum amplitude at the crystal. The high resistance path keeps the inverter biased at high gain, while the opening of the low resistance path minimizes noise during subsequent oscillator operation.

Inventors

• 👤 Kenneth W. Ouyang
• 👤 Karl M. J. Lofgren
• 👤 Gerald W. Shearer

Bibliographic Details