Ultra-low power crystal oscillator with adaptive self-start

Abstract

A crystal oscillator is started in a high power mode for a certain period of time to ensure starting oscillation with average grade crystals, then once the certain time period is over the oscillator switches into a low power mode and sustains oscillation with energy pulses triggered by and synchronized with the oscillator output frequency. These energy pulses may be generated on the positive, negative or both positive and negative edges of the clock output waveform.

Description

[0001] Related Patent Applications [0002] This application claims priority to commonly-owned U.S. Provisional Patent Application No. 62 / 181,554, filed June 18, 2015, which is hereby incorporated by reference herein for all purposes middle. technical field [0003] The present disclosure relates to crystal oscillators, and in particular to a very low power crystal oscillator with adaptive self-start. Background technique [0004] To ensure low power consumption in sleep mode, the microcontroller can be switched to a very low frequency system clock provided by an internal or external oscillator. A conventional 32KHz oscillator consumes about one microampere, and the power budget for the entire system in industry standard deep sleep mode is one (1) microampere. To meet this industry standard deep sleep requirement, the oscillator must consume less than 150 nanoamps (including bias generation) and still be able to support a wide range of crystals. With this wide variation ...

AI Technical Summary

Problems solved by technology

With this wide variation in temperature-dependent crystal quality (R ESR from about 30 kohms to about 90 kohms), the crystal oscillator will not start or maintain oscillation at these low current values

Lower power crystal oscillators (around 200 nanoamps) will only work with very low ESR crystals, which are expensive and not readily available

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