Digital indirectly compensated crystal oscillator

• US 6,630,872 B1
• Filed: 07/20/2001
• Issued: 10/07/2003
• Est. Priority Date: 07/20/2001
• Status: Expired due to Term

• Current Assignee: CMC Electronics Incorporated (Transdigm Group Incorporated)
• Original Assignee: CMC Electronics Incorporated (Transdigm Group Incorporated)
• Inventors: Lanoue, Jean-Claude, Domey, Daniel
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Mai, Lam T.
• Application Number:
  US09/910,182
• Time in Patent Office: 809 Days
• Field of Search: 331/176, 331/17, 331/18, 331/25, 331/158, 331/177.V, 331/66
• 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 1/026 by using a memory for digitally storing correction values H03L1/025 takes precedence
• 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

A temperature compensation technique is disclosed which allows to obtain a compensated clock signal. The temperature compensation technique comprises the use of a thermal model of the oscillator with a temperature sensor in order to accurately compute the oscillator frequency, irrespective of time-variations and rates.

Claims

1. An estimation generator of the effects of temperature on an oscillator in a GPS receiver system, the estimation generator comprising:

a temperature sensor thermally coupled to said oscillator, said temperature sensor outputting a temperature signal;

a memory storing data characterizing oscillator frequency as a function of said temperature signal and time according to a thermal model;

a calculator receiving said temperature signal over time for estimating oscillator frequency using said thermal model and said data.

2. The estimation generator as claimed in claim 1 wherein said data comprises a plurality of look-up table and said calculator derives said estimate from said plurality of look-up table.

3. The estimation generator as claimed in claim 1, wherein said thermal modelis a first order model.

4. The estimation generator as claimed in claim 2, wherein one of said plurality of look-up table relates said temperature signal to the sensor temperature, one of said plurality of look-up table relates said oscillator frequency to oscillator temperature;

and the thermal model relates said oscillator temperature to said sensor temperature and to ambient temperature over time.

5. A method for generating an estimation of the effects of temperature on an oscillator in a GPS receiver system, the method comprising the steps of:

(a) varying temperature and measuring oscillator frequency and temperature over time for calibrating the oscillator frequency as a function of the temperature over time according to a thermal model;

(b) in use, estimating the oscillator frequency using said thermal model, said calibration data and said temperature over time.

6. The method as claimed in claim 5, wherein calibrating the oscillator frequency comprises the steps of:

(a) varying the temperature and measuring temperature and oscillator frequency over time;

(b) calculating estimates of the oscillator temperature from temperature measurements over time using the thermal model;

(c) calculating estimates of the oscillator frequency from oscillator temperature estimates;

(d) observing errors between the oscillator frequency estimates and the oscillator frequency measurements;

(e) adjusting the parameters of the thermal model such as to reduce the errors, until said errors are acceptable;

thereby calibrating the thermal model;

(f) calibrating the oscillator frequency as a function of the estimated oscillator temperature using the oscillator frequency measurements;

thereby removing the effect of time variations and rates.

7. The method as claimed in claim 6, wherein the step of observing errors is performed by displaying the error versus a temperature estimate using a Lissajous plot, and estimating the size of the Lissajous pattern on the Lissajous plot.

8. The method as claimed in claim 5, further comprising the step of calibrating said temperature sensor as a function of ambient temperature.

9. The method as claimed in claim 8, wherein calibrating said temperature sensor is performed according to a thermal model of the temperature sensor and the ambient temperature.

10. The method as claimed in claim 9, wherein calibrating the temperature sensor comprises the steps of:

(a) varying the ambient temperature and measuring temperature and ambient temperature over time;

(b) calculating estimates of sensor temperature from the ambient temperature measurements over time using the thermal model of the temperature sensor;

(c) calculating estimates of the sensor temperature from the temperature measurements;

(d) observing errors between the estimates of the sensor temperature from the ambient temperature measurements, and the estimates of the sensor temperature from the temperature measurements;

(e) adjusting the parameters of the thermal model of the temperature sensor in order to reduce the errors, until said errors are acceptable;

thereby calibrating the thermal model;

(f) calibrating the temperature as a function of the estimated sensor temperature using the temperature measurements;

thereby removing the effect of time variations and rates.

11. The method as claimed in claim 10, wherein the step of observing errors is performed by displaying the error versus a temperature estimate using a Lissajous plot, and estimating the size of the Lissajous pattern on the Lissajous plot.

12. The method as claimed in claim 9, wherein calibrating the oscillator frequency as a function of said sensor temperature and time according to a thermal model of the oscillator comprises the steps of:

(a) varying the ambient temperature and measuring temperature and oscillator frequency over time;

(b) calculating estimates of the sensor temperature from the temperature measurements using said calibration data of the temperature sensor;

(c) calculating estimates of the oscillator temperature from the sensor temperature estimates over time using the thermal model of the oscillator;

(d) calculating estimates of the oscillator frequency using the oscillator temperature estimates;

(e) observing errors between the oscillator frequency estimates and the oscillator frequency measurements;

(f) adjusting the parameters of the thermal model of the oscillator in order to reduce the errors, until said errors are acceptable;

thereby calibrating the thermal model;

(g) calibrating the oscillator frequency as a function of the estimated oscillator temperature using the oscillator frequency measurements;

thereby removing the effect of time variations and rates.

13. The method as claimed in claim 12, wherein the step of observing errors is performed by displaying the error versus a temperature estimate using a Lissajous plot, and estimating the size of the Lissajous pattern on the Lissajous plot.