Temperature compensation of crystal oscillators using microcontroller-/spl mu/CTCXO

The design of compensation circuit in microcontroller temperature compensated crystal oscillator (/spl mu/CTCXO) and design of production line (ACCL) for oscillator automatic calibration are presented. The communication property of /spl mu/CTCXO is introduced in order to provide automatic calibration. The shortened successive approximation algorithm gives short calibration time and reliable convergence of oscillator adjustment by the ACCL system. The /spl mu/CTCXO is realized as a low-cost device encapsulated in a single cubic inch volume. The 0.5 ppm accuracy of frequency in -40/spl deg/C/+85/spl deg/C temperature range is obtained by a 9-bit A/D converter, 10-bit D/A output and 512 bytes of software placed in an EEPROM. Including the standard laboratory frequency counter, temperature chamber and PC host computer the ACCL system requires only the additional analog multiplexer and interface board. The calibration software of 250 Kbytes is executed by the host computer. The ACCL system can compensate many oscillators simultaneously without selection of components and without human control in only one temperature run during production and exploitation.