ABSTRACT A new concept in the design of the compensation circuit in microcontroller temperature compensated crystal oscillators (µCTCXO) and the corresponding production line (ACL-automatic compensation line) for fully automatic oscillator calibration are presented.
The communications ability of µCTCXO 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 µCTCXO is realized as a low-cost device encapsulated in a single cubic inch volume. The ±0.5 ppm frequency accuracy in the -40°C/+85°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.
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