TEMPERATURE COMPENSATION OF A CRYSTAL REFERENCE USING DIRECT SYNTHESIS

摘要

Certain operational characteristics of a crystal (104) are measured during a tes ting and grading process. Once determined, information representing these operational characteristics are stored in memory (120) and utilized by a controller (122) to increment a phase increment register (114) upon determining the crystals ambient temperature via a temperature sensing circuit (124). The value stored in the phase increment register (114) is then sent to a phase a ccumulator (116) where successive phase increments are summed together. This summed value is in turn sent to a sine lookup table (1 18) where the instantaneous phase value is converted into sine amplitude. Finally, a digital to analog converter (126) conv erts the amplitude bit stream into an analog signal for use as a reference oscillator frequency having extremely high frequency reso lution. The above-mentioned process is repeated every clock cycle until a complete sine wave is produced at which point the phas e accumulator is reset to zero and the process begins again.