Field calibration of a digitally compensated crystal oscillator over a temperature range
First Claim
1. An apparatus for compensating an oscillator to correct frequency changes of an output signal of the oscillator due to aging of the oscillator with the oscillator having a first set of compensation values to correct the output signal for frequency changes due to temperature changes over a temperature range and the apparatus using an external reference signal, comprising:
- means for detecting a difference in frequency between the output signal and the external reference signal;
means for determining the temperature of the oscillator;
means for storing the first set of compensation values with each compensation value corresponding to an individual temperature in the temperature range;
means for establishing that the temperature has been stable for a predefined amount of time;
means for establishing the stability of the external reference signal;
means for determining a new compensation value to correct the output signal to have the same frequency as the external reference signal at the determined temperature upon the temperature and external reference signal stable;
means for checking that the absolute difference between the new compensation value and the one of the first set of compensation values at the determined temperature is less than a predefined value; and
means for generating a second set of compensation values upon the absolute difference being less than the predefined value by adding the difference between the new compensation value and the one of the first set of compensation values at the determined temperature to each of the first set of compensation values where the second set of compensation values corrects the oscillator throughout the operating temperature range of the oscillator for change due to aging.
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Accused Products
Abstract
Solving the aging problem of crystal oscillators by doing field recalibration. The solution is to utilize an accurate external reference signal to determine when the frequency of the digital temperature compensated crystal oscillator (DTCXO) has drifted from the reference signal in excess of a specification. When this occurs, the DTCXO has used its internal compensation values to correct its output hence the difference between the external reference signal and the frequency of the DTCXO in excess of the specification is due to aging. A new compensation value for the present temperature is calculated using the reference signal. Using the well known fact that the temperature aging uniformly shifts the frequency over the temperature range, a controller utilizes the difference between the new compensation value and the stored compensation value for the present temperature to shift the entire set of compensation values to compensate for the aging effect.
40 Citations
8 Claims
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1. An apparatus for compensating an oscillator to correct frequency changes of an output signal of the oscillator due to aging of the oscillator with the oscillator having a first set of compensation values to correct the output signal for frequency changes due to temperature changes over a temperature range and the apparatus using an external reference signal, comprising:
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means for detecting a difference in frequency between the output signal and the external reference signal; means for determining the temperature of the oscillator; means for storing the first set of compensation values with each compensation value corresponding to an individual temperature in the temperature range; means for establishing that the temperature has been stable for a predefined amount of time; means for establishing the stability of the external reference signal; means for determining a new compensation value to correct the output signal to have the same frequency as the external reference signal at the determined temperature upon the temperature and external reference signal stable; means for checking that the absolute difference between the new compensation value and the one of the first set of compensation values at the determined temperature is less than a predefined value; and means for generating a second set of compensation values upon the absolute difference being less than the predefined value by adding the difference between the new compensation value and the one of the first set of compensation values at the determined temperature to each of the first set of compensation values where the second set of compensation values corrects the oscillator throughout the operating temperature range of the oscillator for change due to aging. - View Dependent Claims (2, 3, 4)
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5. A method for compensating an oscillator to correct frequency changes of an output signal of the oscillator due to aging of the oscillator with the oscillator having a first set of compensation values to correct the output signal for frequency changes due to temperature changes over a temperature range and the method using an external reference signal, the method comprising the steps of:
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detecting a difference in frequency between the output signal and the external reference signal; determining the temperature of the oscillator; storing the first set of compensation values with each compensation value corresponding to an individual temperature in the temperature range; establishing that the temperature has been stable for a predefined amount of time; establishing the stability of the external reference signal; determining a new compensation value to correct the output signal to have the same frequency as the external reference signal at the determined temperature upon the temperature and external reference signal being stable; checking that the absolute difference between the new compensation value and the one of the first set of compensation values at the determined temperature is less than a predefined value; and generating a second set of compensation values upon the absolute difference being less than the predefined value by adding the difference between the new compensation value and the one of the first set of compensation values at the determined temperature to each of the first set of compensation values where the second set of compensation values correct the oscillator throughout the operating temperature range of the oscillator for changes due to aging. - View Dependent Claims (6, 7, 8)
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Specification