Low power, high accuracy clock circuit and method for integrated

Details Low power, high accuracy clock circuit and method for integrated Low power, high accuracy clock circuit and method for integrated

1997-03-11

1998-12-01

Wells, Kenneth B.

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Synchronizing

327 99, 327160, 327292, 375369, 331 55, 395556, H03L 706

Patent

active

058444351

ABSTRACT:
A clock circuit for providing an integrated circuit with a high accuracy, crystal oscillator clock which interfaces to an "off-chip" crystal to provide a high accuracy clock signal while an internal, low power oscillator provides a low power clock source. Either clock may be selected to drive a programmable processor under program control. When high accuracy and stability are required, the crystal oscillator may be chosen as the processor clock, and when lower power is desired, the low power oscillator may be chosen as the processor clock while the high accuracy clock is disabled. The high accuracy oscillator is used to clock a first timer circuit, while the low power oscillator is used to clock a second timer circuit. The second timer circuit output, in turn, is synchronized to the processor clock so that the programmable processor can utilize the second timer circuit even when the processor clock is asynchronous to the second timer circuit. When the high accuracy oscillator has been selected as the timing source to the programmable processor and to the first timer circuit, and the low power oscillator is clocking the second timer circuit, the programmable processor under program control can effectively measure the frequency of the "on-chip" low power oscillator in terms of the frequency of the high accuracy clock. Accordingly, when the high accuracy clock is disabled, the programmable processor can use the low power oscillator more accurately.

REFERENCES:
patent: 4344046 (1982-08-01), Zumsteg
patent: 5126695 (1992-06-01), Abe
patent: 5416435 (1995-05-01), Jokinen et al.
patent: 5430393 (1995-07-01), Shankar et al.
patent: 5475324 (1995-12-01), Tomiyori
A Microprocessor-Based Analog Wristwatch Chip with 3 Seconds/Year Accuracy, Didier Lanfranchi, Evert Dijkstra, Daniel Aebischer, Feb. 16, 1994.

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