The design of a microcontroller temperature compensated crystal oscillator (/spl mu/CTCXO) and automatic compensation line

A new concept in the design of the compensation circuit in microcontroller temperature compensated crystal oscillators (/spl mu/CTCXO) and the corresponding production line (ACL-automatic compensation line) for fully automatic oscillator calibration are presented. The communications ability of /spl mu/CTCXO is introduced to provide automatic calibration. The shortened successive approximation calibration algorithm gives a short calibration time and a reliable convergence of oscillator adjustment by the ACL system. The /spl mu/CTCXO is realized as a low-cost device encapsulated in a single cubic inch volume. The /spl plusmn/0.5 ppm frequency accuracy in the -40/spl deg/C/+85/spl deg/C temperature range is obtained by a 9-bit A/D converter, 10-bit D/A and 512 bytes of software placed in an EEPROM. The ACL system, in addition to the standard laboratory frequency counter, temperature chamber and a PC host computer, requires only two additional boards: an analog multiplexer board and an interface board. During production and recalibration, the ACL system can compensate many oscillators simultaneously in a single temperature run, without requiring component selection and human supervision.