Digitally temperature compensated voltage-controlled oscillator

Abstract

A digitally temperature compensated oscillator (TCO) system is provided which is capable of ascertaining and memorizing in an EEPROM-based look-up table, appropriate digital values of a temperature-compensating tuning voltage to the TCO during calibration. An on-board temperature sensing mechanism tracks variations in temperature in the TCO and produces an analog voltage value corresponding to the instantaneous temperature. The voltage value of the sensor output is digitized and designated to constitute an address into the EEPROM based look-up table. As the temperature changes, the digitized output of the temperature sensor and hence the address to the EEPROM changes accordingly. The TCO tuning voltage value corresponding to the address represented by the measured temperature is extracted from the values stored within the EEPROM table and then converted into a corresponding analog voltage which is used to drive the voltage-controlled oscillator (VCO) in order to maintain the output frequency of the TCO stabilized at a desired value. The EEPROM contained within the TCO is preferably calibrated during production, under the control of a calibration and test circuit which regulates the calibration and testing of a TCO in a chamber whose temperature is ramped over a desired temperature range. The TCO includes an on-board microprocessor which allows integration of several of the TCO functions, including the analog-to-digital and the storage and retrieval of data to and from the EEPROM containing the look-up table and extremely simplifies the calibration and test procedure.