Apparatus and method for temperature compensation of crystal oscillators

• US 20080061899A1
• Filed: 09/04/2007
• Published: 03/13/2008
• Est. Priority Date: 09/12/2006
• Status: Active Grant

• Current Assignee: CTS Corporation
• Original Assignee: CTS Corporation
• Inventors: Stolpman, James
• Granted Patent: US 7,649,426 B2
• Time in Patent Office: Days
• US Class Current: 331/176
• CPC Class Codes: H03L 1/022 by indirect stabilisation, i.e. by generating an electrical correction signal which is a function of the temperature H03L1/021 takes precedence
• CPC Class Codes: H03L 1/023 by using voltage variable capacitance diodes
• CPC Class Codes: H03L 1/028 of generators comprising piezoelectric resonators H03L1/021, H03L1/022 take precedence; oscillation generators with a piezoelectric resonator H03B5/32

Abstract

An oscillator includes an oscillator circuit and a resonator that produces an output frequency. A temperature compensation circuit is coupled to the oscillator circuit. The temperature compensation circuit stabilizes the output frequency in response to changes in temperature. At least one temperature sensor and a temperature sensor signal modification circuit are coupled to the temperature compensation circuit. The temperature sensor signal modification circuit receives a temperature signal from the temperature sensor and generates a modified temperature sensor signal that is transmitted to the temperature compensation circuit.

Claims

1. An oscillator comprising:

a resonator;

an oscillator circuit connected to the resonator and operable to produce an output frequency;

a temperature compensation circuit associated with the oscillator circuit, the temperature compensation circuit being adapted to stabilize the output frequency in response to changes in temperature;

at least a first temperature sensor; and

a temperature sensor signal modification circuit associated with the first temperature sensor and the temperature compensation circuit, the temperature sensor signal modification circuit being adapted to receive a first temperature signal from the first temperature sensor and generate a modified temperature sensor signal that is transmitted to the temperature compensation circuit.

2. The oscillator according to claim 1, wherein the first temperature sensor is a thermistor located adjacent the resonator.

3. The oscillator according to claim 1, wherein the first temperature sensor is located on one side of the resonator, the oscillator further comprising a second temperature sensor located on the opposite side of the resonator.

4. The oscillator according to claim 3, wherein the first and second temperature sensors are thermistors.

5. The oscillator according to claim 1, wherein the first temperature sensor is a semiconductor device adapted to produce a voltage or current proportional to the temperature sensed by the first temperature sensor.

6. The oscillator according to claim 1, wherein the temperature sensor signal modification circuit further comprises:

a first amplifier adapted to receive the first temperature signal and generate a first amplifier output signal;

a second amplifier connected to the first amplifier and adapted to receive the first amplifier output signal and generate a second amplifier output signal; and

a third amplifier connected to the first and second amplifiers and adapted to receive the first temperature signal and the second amplifier output signal and generate the modified temperature sensor signal.

7. The oscillator according to claim 1, wherein the modified temperature sensor signal compensates for the thermal gradient between the resonator and the first temperature sensor.

8. The oscillator according to claim 7 further comprising a second temperature sensor, the first amplifier being adapted to receive the second temperature signal and generate a first amplifier output signal, the thermal gradient between the resonator and the first temperature sensor being approximately the same as the thermal gradient between the first temperature sensor and the second temperature sensor.

9. An oscillator, comprising:

frequency stabilizing means for stabilizing a reference frequency;

oscillator circuit means connected to the frequency stabilizing means and adapted to generate the reference frequency;

temperature compensation means connected to the oscillator circuit means for adjusting the reference frequency in response to a change in temperature;

temperature sensor means for sensing a temperature and generating at least one temperature sensor signal; and

temperature sensor signal modification means connected to the temperature sensor means and the temperature compensation means, the temperature sensor signal modification means receiving the temperature sensor signal and generating a modified temperature sensor signal that is provided to the temperature compensation means.

10. The oscillator according to claim 9, wherein the oscillator circuit means includes:

a transistor;

a resistor feedback network connected to the transistor; and

a varactor.

11. The oscillator according to claim 9, wherein the temperature sensor means comprises:

a first temperature sensor adapted to generate a first temperature sensor signal; and

a second temperature sensor adapted to generate a second temperature sensor signal.

12. The oscillator according to claim 11, wherein the temperature sensor signal modification means comprises:

a first amplifier adapted to receive the first and second temperature signals and generate a first amplifier output signal;

a second amplifier connected to the first amplifier and adapted to receive the first amplifier output signal and generate a second amplifier output signal; and

a third amplifier connected to the first and second amplifiers and adapted to receive the first temperature signal and the second amplifier output signal and generate the modified temperature sensor signal.

13. The oscillator according to claim 9, wherein the oscillator is located in a housing.

14. The oscillator according to claim 11, wherein the first and second temperature sensors are spaced apart from each other.

15. The oscillator according to claim 11, wherein the first temperature sensor is located in proximity to the frequency stabilizing means.

16. The oscillator according to claim 15, wherein the second temperature sensor is located in proximity to the oscillator circuit means.

17. A method of temperature compensating an oscillator comprising the steps of:

providing an oscillator circuit in communication with a resonator;

generating a reference frequency from the oscillator circuit;

sensing at least a first temperature;

generating a modified temperature sensor signal from the at least first sensed temperature;

generating a temperature compensation voltage from the modified temperature sensor signal; and

adjusting the reference frequency using the temperature compensation voltage.

18. The method according to claim 17, wherein the modified temperature sensor signal compensates for a thermal lag time between the resonator and the sensed first temperature.

19. An oscillator comprising:

a resonator;

an oscillator circuit connected to the resonator and operable to produce an output frequency;

first and second temperature sensors associated with the oscillator;

a temperature sensor signal modification circuit in communication with the first and second temperature sensors;

a processor in communication with the oscillator circuit and the temperature sensor signal modification circuit; and

software operable on the processor for;

receiving a modified temperature sensor signal from the temperature sensor signal modification circuit;

generating a temperature compensation signal from the modified temperature sensor signal; and

adjusting the output frequency using the temperature compensation signal.

20. The oscillator according to claim 19, wherein the first and second temperature sensors are located on opposite sides of the resonator.