Oscillator temperature compensating circuit using stored and calculated values
First Claim
1. A voltage-controlled crystal oscillator, said oscillator including:
- A. an oscillator crystal having an output signal whose frequency varies with temperature;
B. a temperature sensor for sensing ambient temperature and producing a signal related to the temperature;
C. a memory for storing for each of a predetermined number of ambient temperatures a temperature offset value equal to the difference between the oscillator frequency at the ambient temperature and the oscillator frequency at a known different temperature, said temperature offset values being stored at memory locations associated with the ambient temperatures;
D. an address decoder connected between said temperature sensor and said memory, said address decoder receiving the output of said temperature sensor and addressing locations in said memory associated with the ambient temperature;
E. a function calculator connected to receive the contents of the memory locations addressed by said address decoder and the output of said temperature sensor for calculating a compensating signal value depending on the retrieved temperature offset values and directly related to the ambient temperature; and
F. a converter connected to receive the calculated compensating signal value for converting the signal value to a compensating signal and applying the signal to the controlling input of the crystal oscillator.
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Accused Products
Abstract
A voltage-controlled oscillator includes a compensating signal value calculator which calculates the value of a function representing the portion of the oscillator temperature-frequency transfer curve corresponding to the ambient temperature. A signal corresponding to the calculated value is then applied to the voltage-controlled oscillator as the control voltage. Basically, an oscillator temperature-frequency transfer curve is partitioned into n segments. For each segment an offset value, xn, equal to the difference between the frequency at the start of the segment and the desired frequency, is stored in a look-up table. When a compensating signal value is required, the compensating signal value calculator retrieves from the look-up table the xn values corresponding to the segment immediately preceding and succeeding segment k, segments "k-1" and "k+1". The retrieved values are labeled xk, xk-1, and xk+1, respectively. It then calculates a function representing the portion of the transfer curve passing through three points corresponding to the values: ##EQU1## The compensating signal value is then calculated by substituting the actual delta T value into the equation. If the oscillator output frequency has shifted due to aging of the crystal, an aging offset value, xA, is added to the equation, and the compensating signal compensates for frequency variations related to both temperature and aging.
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Citations
13 Claims
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1. A voltage-controlled crystal oscillator, said oscillator including:
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A. an oscillator crystal having an output signal whose frequency varies with temperature; B. a temperature sensor for sensing ambient temperature and producing a signal related to the temperature; C. a memory for storing for each of a predetermined number of ambient temperatures a temperature offset value equal to the difference between the oscillator frequency at the ambient temperature and the oscillator frequency at a known different temperature, said temperature offset values being stored at memory locations associated with the ambient temperatures; D. an address decoder connected between said temperature sensor and said memory, said address decoder receiving the output of said temperature sensor and addressing locations in said memory associated with the ambient temperature; E. a function calculator connected to receive the contents of the memory locations addressed by said address decoder and the output of said temperature sensor for calculating a compensating signal value depending on the retrieved temperature offset values and directly related to the ambient temperature; and F. a converter connected to receive the calculated compensating signal value for converting the signal value to a compensating signal and applying the signal to the controlling input of the crystal oscillator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of compensating a voltage-controlled crystal oscillator for output signal frequency variations including the steps of:
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A. sensing ambient temperature and producing a signal related to the ambient temperature; B. retrieving from a look-up table temperature offset values associated with the ambient temperature, said offset values representing compensating signal values corresponding to predetermined temperatures associated with the ambient temperature; C. using the retrieved temperature offset values, calculating coefficients of a function describing for the crystal a temperature-frequency relationship over a predetermined temperature range, said range including the ambient temperature; D. calculating a compensating signal value corresponding to the ambient temperature using the function; E. converting the calculated compensating signal value to an analog compensating signal; and F. applying the compensating signal to the crystal oscillator as the voltage-control signal. - View Dependent Claims (10, 11, 12, 13)
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Specification