Reliable crystal oscillator start-up

A technology of crystal oscillators and oscillators, applied in the direction of power oscillators, generator start-up, power automatic control, etc., can solve problems such as increasing power consumption

Active Publication Date: 2015-08-05
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

This rather complex signal processing als

Method used

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  • Reliable crystal oscillator start-up
  • Reliable crystal oscillator start-up
  • Reliable crystal oscillator start-up

Examples

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Embodiment Construction

[0011] figure 1 The device 1 shown comprises a crystal oscillator 2 with a crystal 3, usually a quartz crystal, and an oscillator circuit 4 connected to the crystal 3 and used to control the crystal. The oscillator circuit 4 is in turn controlled by a processing unit 5 . The processing unit is preferably a microprocessor and is connected to a non-volatile memory 6 such as RAM with always-on power supply. The non-volatile memory 6 includes at least one look-up table and other storage locations to store at least one start-up value and run-time value as described below.

[0012] A switch 7 is used to connect the clock input of the processing unit 5 with the output of the crystal oscillator 2 , or alternatively, the clock input of the processing unit 5 with the output of the auxiliary oscillator 8 . The auxiliary oscillator 8 can be implemented by another crystal oscillator, or preferably, by a ring oscillator or an LC resonator oscillator. During shutdown, the switch is not op...

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Abstract

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 (12) 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 (17, 18). 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 (19). The crystal oscillator is then restarted with the start-up value (13) and after a delay the operating value is applied (14). The start-up value can be determined using an initial value for the parameter which is associated with a moderate drive level and where necessary modifying the parameter step-wise, increasing the drive level until the oscillator starts up. The start-up value so determined is also stored in the non-volatile memory. In subsequent start-ups the stored start-up value and operating value can be applied immediately.

Description

technical field [0001] The invention relates to a method of starting a crystal oscillator and a device comprising a crystal oscillator for carrying out the method. Crystal oscillators are used as clocks for electronic devices, where a reliable and accurate reference frequency is a requirement. Background technique [0002] The method in the preamble of claim 1 is disclosed in US patent publication US 7940137B2. The bias current, a parameter used to control the excitation level of the oscillator, is set high at start-up and then gradually decreased until the oscillator signal amplitude falls below the threshold. This requires the use of fairly complex circuits with expensive high-quality components. This circuit is used to monitor the amplitude and control the bias current through a feedback loop. The feedback circuit involves rectification, analog-to-digital conversion of the output signal, and digital-to-analog conversion of the digital signal that controls the bias curr...

Claims

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Application Information

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IPC IPC(8): H03B5/06
CPCH03B2200/0082H03L3/00H03B2200/0094H03L7/099H03B5/32H03B5/36
Inventor 达历桑德罗·卡尔米内
Owner U-BLOX
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