RELIABLE CRYSTAL OSCILLATOR START-UP

摘要

The method concerns the reliable start-up of a crystal oscillator where the drive levels the crystal is subjected to are kept low in order to avoid over-driving the crystal. After applying a start-up value of a parameter controlling the drive level where the drive level associated with the start-up value is rather high such that reliable start-up is ensured the parameter is modified step-wise so as to reduce the drive level until the crystal oscillator ceases to operate regularly. To assess whether this is the case, the frequency of the crystal oscillator is compared with the frequency of an auxiliary oscillator. A safety margin is added to the parameter and the result stored in a non-volatile memory as an operating value. The crystal oscillator is then restarted with the start-up value and after a delay the operating value is applied.

主权项

1. A method of starting up a crystal oscillator with a crystal and an oscillator circuit connected to a non-volatile memory, where a parameter which controls a drive level of the crystal is configured, the method comprising:
setting the value of the parameter to a start-up value where the associated drive level is high enough to assure that the crystal oscillator begins to oscillate, modifying the value of the parameter such as to monotonically reduce the drive level of the crystal while monitoring the crystal oscillator, determining, in the course of monitoring the crystal oscillator, a breakdown value of the parameter where the crystal oscillator ceases to operate regularly, employing as a criterion of regular operation the condition that a cycle count of the crystal oscillator signal does not deviate from a cycle count of a reference signal by more than a predetermined amount, and selecting an operating value of the parameter such that the drive level associated with said operating value is above the drive level associated with the breakdown value by a safety margin.