Frequency and/or phase compensated microelectromechanical oscillator

• US 7,907,027 B2
• Filed: 05/12/2009
• Issued: 03/15/2011
• Est. Priority Date: 01/09/2004
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Partridge, Aaron, Lutz, Markus
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US12/464,304
• Publication Number:
  US 20090278619A1
• Time in Patent Office: 672 Days
• Field of Search: 331/18, 331/66, 331/74, 331/75, 331/116.R, 331/116.FE, 331/116.M, 331/154, 331/156, 331/175, 331/176
• US Class Current: 331/154
• 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 5/30 with frequency-determining element being electromechanical resonator
• 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 1/027 by using frequency conversion means which is variable with temperature, e.g. mixer, frequency divider, pulse add/substract logic circuit H03L1/023, H03L1/026 take precedence
• CPC Class Codes: H03L 1/04 Constructional details for maintaining temperature constant
• CPC Class Codes: H03L 7/07 using several loops, e.g. for redundant clock signal generation
• CPC Class Codes: H03L 7/08 Details of the phase-locked loop
• CPC Class Codes: H03L 7/1974 for fractional frequency division

Abstract

Example embodiments of the present invention are directed to a compensated microelectromechanical oscillator, having a microelectromechanical resonator that generates an output signal and frequency adjustment circuitry, coupled to the microelectromechanical resonator to receive the output signal of the microelectromechanical resonator and, in response to a set of values, to generate an output signal having second frequency. The values may be determined using the frequency of the output signal of the microelectromechanical resonator, which depends on the operating temperature of the microelectromechanical resonator and/or manufacturing variations of the microelectromechanical resonator. The frequency adjustment circuitry may include frequency multiplier circuitry, for example, PLLs, DLLs, digital/frequency synthesizers and/or FLLs, as well as any combinations and permutations thereof. The frequency adjustment circuitry, in addition or in lieu thereof, may include frequency divider circuitry, for example, DLLs, digital/frequency synthesizers (for example, DDS) and/or FLLs, as well as any combinations and permutations thereof.

Claims

1. A system for generating a timing signal comprising:

a microelectromechanical system (MEMS) resonator;

drive circuitry coupled to the MEMS resonator and configured to drive the MEMS resonator with a drive signal to generate a reference signal having a first frequency;

a memory device storing compensation data;

control circuitry coupled to the memory device and configured to generate a set of values based on the compensation data and one or more operating temperature readings; and

frequency adjustment circuitry coupled to the control circuitry and configured to;

receive the reference signal generated by the MEMS resonator,

receive the set of values generated by the control circuitry, and

based on the reference signal and the set of values, generate a timing signal having a second frequency that is different from the first frequency.

2. The system of claim 1, further comprising temperature compensation circuitry coupled to the control circuitry and the MEMS resonator and configured to provide the one or more operating temperature readings to the control circuitry.

3. The system of claim 1, wherein the control circuitry is further configured to:

access the memory device to retrieve the compensation data; and

generate the set of values based on the retrieved compensation data.

4. The system of claim 1, wherein the compensation data comprises a look-up table relating the first frequency to an operating temperature of the MEMS resonator.

5. The system of claim 4, wherein the set of values is generated based on data in the look-up table.

6. The system of claim 1, wherein the memory device comprises read-only memory or random-access memory.

7. The system of claim 1, wherein the control circuitry, the frequency adjustment circuitry, the temperature compensation circuitry, and the memory device reside within a single chip.

8. The system of claim 1, wherein the first frequency depends on an operating temperature of the MEMS resonator.

9. The system of claim 1, wherein the set of values is generated based on empirical data or a mathematical relationship.

10. The system of claim 1, wherein the compensation data is stored or programmed in the memory device during testing of the MEMS resonator, calibration of the MEMS resonator, or operation of the MEMS resonator.

11. The system of claim 1, wherein the frequency adjustment circuitry comprises a fractional-N synthesizer.

12. The system of claim 11, wherein the fractional-N synthesizer comprises a charge pump, a phase detector, a loop filter, a voltage controlled oscillator (VCO), and a divider.

13. The system of claim 12, wherein the phase detector comprises a phase-frequency detector.

14. The system of claim 13, wherein the loop filter comprises an RC circuit.

15. The system of claim 14, wherein the VCO comprises a wideband VCO.

16. The system of claim 15, wherein the divider is programmable.

17. The system of claim 1, wherein the control circuitry is further configured to adjust the drive signal driving the MEMS resonator.

18. The system of claim 17, wherein the control circuitry adjusts the drive signal according to changes in operating conditions or environment of the MEMS resonator.

19. The system of claim 17, wherein the control circuitry adjusts the drive signal based on the reference signal and the one or more operating temperature readings.

20. The system of claim 1, wherein the second frequency is greater than the first frequency.

21. The system of claim 1, wherein the second frequency is less than the first frequency.

22. A system for generating a timing signal comprising:

a microelectromechanical system (MEMS) resonator;

drive circuitry coupled to the MEMS resonator and configured to drive the MEMS resonator with a drive signal to generate a reference signal having a first frequency;

a memory device storing compensation data;

control circuitry coupled to the memory device and configured to generate a set of values based on the compensation data and one or more operating temperature readings;

temperature compensation circuitry coupled to the control circuitry and the MEMS resonator and configured to provide the one or more operating temperature readings to the control circuitry; and

a fractional-N synthesizer comprising a charge pump, a phase detector, a loop filter, a voltage controlled oscillator, and a divider, wherein the factional-N synthesizer is coupled to the control circuitry and configured to;

receive the reference signal generated by the MEMS resonator,

receive the set of values generated by the control circuitry, and

based on the reference signal and the set of values, generate a timing signal having a second frequency that is different from the first frequency.

23. The system of claim 22, wherein the second frequency is greater than the first frequency.

24. The system of claim 22, wherein the second frequency is less than the first frequency.