Digitally-based temperature compensation for a crystal oscillator

• US 10,333,525 B1
• Filed: 12/06/2016
• Issued: 06/25/2019
• Est. Priority Date: 12/07/2015
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Gandolfi, Gabriele, Bernardi, Giacomo, Bongiorni, Marco, Chiabrera, Michele, Colonna, Vittorio, Demarziani, Alberto, Marchese, Stefano, Pelle, Alessio, Rezzi, Francesco, Savo, Alessandro
• Primary Examiner(s): Kinkead, Arnold M
• Application Number:
  US15/369,909
• Time in Patent Office: 931 Days
• Field of Search: 331158, 331116 FE, 331116 R, 331177 V, 331176
• CPC Class Codes: H03B 2200/0018 relating to the cutting angle of a crystal, e.g. AT cut quartz
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03B 5/364 the amplifier comprising field effect transistors H03B5/366 takes precedence
• CPC Class Codes: H03L 1/02 against variations of temperature only
• 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 1/025 and a memory for digitally storing correction values
• 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
• CPC Class Codes: H03L 1/04 Constructional details for maintaining temperature constant
• CPC Class Codes: H04W 88/02 Terminal devices

Abstract

An apparatus includes a temperature sensor, a digitally-controlled capacitor and a processor. The temperature sensor is coupled to a crystal oscillator and configured to generate an input signal depending on a temperature of the crystal oscillator. The digitally-controlled capacitor is connected to the crystal oscillator and configured to receive a control signal and, based on the control signal, to control a frequency of an output signal generated by the crystal oscillator. The processor is configured to receive the input signal from the temperature sensor, to convert the input signal into the control signal based on parameters that characterize the crystal oscillator and the digitally-controlled capacitor, and to apply the control signal to the digitally-controlled capacitor.

Claims

1. An apparatus, comprising:

a temperature sensor, coupled to a crystal oscillator and configured to generate an input signal depending on a temperature of the crystal oscillator;

a digitally-controlled capacitor, which is connected to the crystal oscillator and is configured to receive a control signal and, based on the control signal, to control a frequency of an output signal generated by the crystal oscillator; and

a processor, which is configured to;

receive the input signal from the temperature sensor;

convert the input signal into the control signal based on parameters that characterize the crystal oscillator and the digitally-controlled capacitor, the parameters comprising at least capacitances of a series capacitor and a parallel capacitor of an electrical model of the crystal oscillator, and multiple coefficients of a polynomial that models a relationship between frequency deviation and temperature of the crystal oscillator; and

apply the control signal to the digitally-controlled capacitor.

3. The apparatus according to claim 1, wherein the processor is configured to convert the input signal into the control signal by estimating the temperature of the crystal oscillator using a sensor model of the temperature sensor that translates the input signal into temperature.

4. The apparatus according to claim 1, wherein the processor is configured to convert the input signal into the control signal by translating the estimated temperature into a frequency deviation using a frequency-temperature model of the crystal oscillator.

5. The apparatus according to claim 1, wherein the processor is configured to estimate, based on the input signal, a frequency deviation of the crystal oscillator from a target frequency, and to translate the estimated frequency deviation into the control signal using a frequency deviation model of the crystal oscillator.

6. The apparatus according to claim 1, wherein the temperature sensor comprises a Negative Temperature Coefficient (NTC) resistor.

7. The apparatus according to claim 1, wherein the digitally-controlled capacitor comprises a two-dimensional (2D) capacitor array in a capacitive DAC.

8. The apparatus according to claim 1, wherein the processor is further configured to estimate one or more parameters that characterize the crystal oscillator, by setting the digitally-controlled capacitor, independently of the input signal, to multiple predefined different capacitance values at a same given temperature, and measuring multiple respective resulting frequency deviations from a target frequency of the crystal oscillator.

9. The apparatus according to claim 1, wherein the processor is configured to approximate a relationship between the control signal and the input signal by applying to the input signal two or more polynomial expressions in series.

10. A wireless communication terminal comprising the apparatus of claim 1.

11. A chipset for processing signals in a wireless communication terminal, comprising the apparatus of claim 1.

2. An apparatus, comprising:

a temperature sensor, coupled to a crystal oscillator and configured to generate an input signal depending on a temperature of the crystal oscillator;

a digitally-controlled capacitor, which is connected to the crystal oscillator and is configured to receive a control signal and, based on the control signal, to control a frequency of an output signal generated by the crystal oscillator; and

a processor, which is configured to;

receive the input signal from the temperature sensor by sampling the input signal at a first sampling rate and decimating the sampled input signal to a second sampling rate lower than the first sampling rate;

convert the input signal into the control signal based on parameters that characterize the crystal oscillator and the digitally-controlled capacitor; and

apply the control signal to the digitally-controlled capacitor.

12. A method, comprising:

receiving an input signal from a temperature sensor, coupled to a crystal oscillator, the input signal being dependent upon a temperature of the crystal oscillator;

converting the input signal into a control signal based upon parameters that characterize the crystal oscillator and a digitally-controlled capacitor, connected to the crystal oscillator, the parameters comprising at least capacitances of a series capacitor and a parallel capacitor of an electrical model of the crystal oscillator, and multiple coefficients of a polynomial that models a relationship between frequency deviation and temperature of the crystal oscillator; and

applying the control signal to the digitally-controlled capacitor, for controlling a frequency of an output signal generated by the crystal oscillator.

13. The method according to claim 12, wherein receiving the input signal comprises sampling the input signal at a first sampling rate and decimating the sampled input signal to a second sampling rate lower than the first sampling rate.

14. The method according to claim 12, wherein converting the input signal into the control signal comprises estimating the temperature of the crystal oscillator using a sensor model of the temperature sensor that translates the input signal into temperature.

15. The method according to claim 14, wherein converting the input signal into the control signal comprises translating the estimated temperature into a frequency deviation using a frequency-temperature model of the crystal oscillator.

16. The method according to claim 12, wherein converting the input signal into the control signal comprises estimating, based on the input signal, a frequency deviation of the crystal oscillator from a target frequency, and translating the estimated frequency deviation into the control signal using a frequency deviation model of the crystal oscillator.

17. The method according to claim 12, further comprising estimating one or more parameters that characterize the crystal oscillator by setting the digitally-control capacitor, independently of the input signal, to multiple predefined different capacitance values at a same given temperature, and measuring multiple respective resulting frequency deviations from a target frequency of the crystal oscillator.

18. The method according to claim 12, wherein converting the input signal into the control signal comprises approximating a relationship between the control signal and the input signal by applying to the input signal two or more polynomial expressions in series.