Method and apparatus for providing a modified temperature compensation signal in a TCXO circuit
AssigneeMotorola, Inc.
InventorsDennis F. Marvin, Daniel J. Russell
Life of this patent
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Abstract
A modified temperature compensation signal (110) is provided in a temperature compensated crystal oscillator (TCXO) circuit (100) in the following manner. A temperature dependent current generator (104) produces a temperature compensation signal (108) whose amplitude changes responsive to changes in ambient temperature. The temperature compensation signal (108) is scaled, based on a plurality of discrete frequency adjust values (212), to produce the modified temperature compensation signal (110).
Claims19
In a temperature compensated crystal oscillator (TCXO) circuit that includes an oscillator for generating a signal whose frequency changes responsive to a temperature compensation signal, the oscillator including a piezoelectric device whose frequency characteristics change responsive to changes in ambient temperature, a method for modifying the temperature compensation signal to offset a trim effect caused by a variation in load capacitance of the piezoelectric device, the method comprising the steps of:
- A) providing a temperature compensation signal whose amplitude changes responsive to changes in the ambient temperature;
- B) providing a plurality of discrete frequency adjust values;
- and
- C) scaling the temperature compensation signal, responsive to the plurality of discrete frequency adjust values to produce a modified temperature compensation signal that offsets the trim effect.
A temperature compensated crystal oscillator (TCXO) circuit, comprising:
- an oscillator circuit that includes a piezoelectric device whose frequency characteristics change responsive to changes in ambient temperature, the oscillator circuit generating a signal whose frequency changes responsive, at least in part, to a modified temperature compensation signal;
- a current generator that provides current levels responsive to changes in the ambient temperature to produce a temperature compensation signal;
- a partitioned current mirror, operably coupled to the current generator and the oscillator circuit, that includes a plurality of current mirroring devices, wherein the plurality of current mirroring devices provide current levels proportional to the current levels produced by the current generator;
- memory means for storing discrete frequency adjust values;
- and
- control means, operably coupled between the memory means and the partitioned current mirror, for selecting at least a first of the plurality of current mirroring devices based on the discrete frequency adjust values to modify the temperature compensation signal.
A temperature compensated crystal oscillator (TCXO) circuit comprising:
- an oscillator circuit that includes a piezoelectric device whose frequency characteristics change responsive to changes in ambient temperature, the oscillator circuit generating a signal whose frequency chariots responsive, at least in part, to a modified temperature compensation signal;
- a current generator that provides current levels responsive to changes in the ambient temperature to produce a temperature compensation signal;
- a partitioned resistance device, operably coupled to the current generator, that includes a plurality of resistive devices:
- memory means for storing discrete frequency adjust values
- signal means, operably coupled to the memory means, for providing a trim signal to the oscillator circuit;
- and
- control means, operably coupled between the memory means and the partitioned resistance device, for selecting at least a first of the plurality of resistive devices based on the discrete frequency adjust values to produce the modified temperature compensation signal.
Dependencies are inferred from the claim text.