Common reference crystal systems

摘要

One embodiment of communication system comprises a crystal oscillator configured to output a reference clock; cellular radio frequency (RF) and baseband phase locked loops configured to receive the reference clock within a cellular module and compensate for calculated frequency errors between a received cellular downlink signal and a cellular local oscillator signal during operation of the cellular module; global positioning system (GPS) frequency compensation circuitry configured to receive the reference clock within a GPS module and compensate for calculated frequency errors during operation of the GPS module; and a temperature sensing circuit which includes a plurality of sensing resistors and is configured to output a signal corresponding to a temperature of a reference crystal which is translated to a frequency deviation, wherein the (GPS) frequency compensation circuitry is configured to offset the frequency deviation and output a temperate compensated signal to meet GPS clock frequency requirements.

主权项

1. A system comprising:
a crystal oscillator configured to support a cellular receiver and a global positioning system (GPS) receiver; an uncompensated crystal resonator coupled to the crystal oscillator, the uncompensated crystal resonator configured to generate a reference signal; a temperature sensing circuit configured to output a signal substantially proportional to a current temperature; and a compensation module integrated with the GPS receiver and configured to calculate frequency errors due to temperature drift over an operational temperature region based on a temperature sensing circuit output and temperature dependent polynomial coefficients of a calibrated temperature-frequency characteristic curve.