Fast wakeup for crystal oscillator

Abstract

Techniques for fast wakeup for crystal oscillator circuits are described. Embodiments operate in the context of a crystal oscillator coupled to a phase locked loop (PLL). For example, prior to entering a sleep mode, the embodiment retains a previously obtained coarse code for coarse tuning the voltage controlled oscillator of the PLL. Upon waking up, the PLL is configured in a chirp mode, whereinthe retained coarse code and a scan voltage are used to generate a chirp signal at a target excitation frequency of the crystal oscillator or at a frequency close to the target excitation frequency. The chirp signal can be used to inject energy into the crystal oscillator such that the crystal oscillator transitions from the sleep mode to a steady state oscillation mode relatively quickly.

Description

technical field [0001] The present invention relates generally to clock circuits. More specifically, embodiments of the invention relate to fast wake-up for a crystal oscillator reference clock coupled with a phase locked loop circuit. Background technique [0002] Various types of oscillators are commonly used to provide reference signals used in electronic applications. Their piezoelectric properties make them frequency-determining components in electronic circuits. Crystal oscillators, especially those made of quartz crystals, are distorted by an electric field when a voltage is applied to electrodes near the crystal or to electrodes on the crystal. This property is called electrostriction or inverse piezoelectricity. When the field is removed, the quartz, which oscillates at a precise frequency, generates an electric field as it returns to its previous shape, and can generate an oscillating voltage that can be used as a precise clock signal. [0003] Typically, a cry...

AI Technical Summary

Problems solved by technology

Variations in crystal resistance result in the use of more power at start-up than is required for optimum noise performance in steady-state operation

However, reducing power to achieve the best noise performance in steady state increases the amount of time the crystal oscillator takes from startup to steady state

Therefore, there is often a design trade-off between crystal oscillator power efficiency and start-up time

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