Method and Apparatus for MEMS Phase Locked Loop

• US 20110254599A1
• Filed: 04/14/2011
• Published: 10/20/2011
• Est. Priority Date: 04/14/2010
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Dikshit, Abhinav Kumar, Krishnaswamy, Anjan Kumar, Kumar, Gadam Chetty Deva Phanindra
• Granted Patent: US 8,624,679 B2
• Time in Patent Office: Days
• US Class Current: 327/156
• CPC Class Codes: H03L 3/00 Starting of generators
• CPC Class Codes: H03L 7/02 using a frequency discriminator comprising a passive frequency-determining element

Abstract

The proper operation of a phase locked loop is determined by monitoring certain signals within the loop for their phase relationship or duty cycle. If a malfunction of the loop is detected, proper operation may be imposed or restored by resetting a phase-frequency detector, or by flipping the output of the phase-frequency detector.

Claims

1. A method of driving an oscillating member, the method comprising:

applying a drive signal to the oscillating member, the drive signal having a drive frequency;

providing a first reference signal indicative of the phase shift imparted on the drive signal by the oscillating member;

decreasing the drive frequency if the phase shift is less than ninety degrees, and increasing the drive frequency if the phase shift is between ninety and one hundred eighty degrees.

2. A method of driving an oscillating member according to claim 1, further comprising:

providing a second reference signal, the second signal having the same frequency as the drive signal, but leading the drive signal by ninety degrees; and

determining the phase shift by determining the phase between the second reference signal and the first reference signal.

3. A method of driving an oscillating member according to claim 2, wherein determining the phase difference between the second reference signal and the first reference signal comprises:

determining whether an edge of the first reference signal leads or lags a corresponding edge of the second reference signal,

wherein the corresponding edge occurs within one quarter of a period of the drive frequency from the edge of the first reference signal.

4. A method of driving an oscillating member according to claim 1, wherein decreasing the drive frequency if the phase shift is less than ninety degrees, and increasing the drive frequency if the phase shift is between ninety and one hundred eighty degrees, comprises:

generating a first control signal if the phase shift is less than ninety degrees, and generating a second control signal if the phase shift is greater than ninety degrees.

5. A method of addressing positive feedback in a circuit driving an oscillating member, the method comprising:

applying a drive signal having a drive frequency to the oscillating member;

providing a first reference signal to a phase detector, the first reference signal indicative of the phase shift imparted on the drive signal by the oscillating member;

providing a second reference signal to the phase detector, the second signal having the same frequency as the drive signal, but leading the drive signal by ninety degrees;

generating a first control signal if a phase detector determines that the first reference signal leads the second reference signal; and

resetting the phase detector if the first control signal is active at a falling edge of the second reference signal.

6. A method of addressing positive feedback in a circuit driving an oscillating member according to claim 5, wherein applying a drive signal comprises:

generating the second reference signal; and

producing the drive signal by imposing a phase shift of negative ninety degrees on the second reference signal,

such that the second reference signal leads the drive signal by 90 degrees.

7. A method of addressing positive feedback in a circuit driving an oscillating member according to claim 5, wherein providing a second reference signal comprises:

generating the drive signal; and

producing the second reference signal by imposing a phase shift of 270 degrees on the reference signal,

such that the second reference signal leads the drive signal by 90 degrees.

8. A method of addressing positive feedback in a circuit driving an oscillating member according to claim 5, the method further comprising:

generating a second control signal if a phase detector determines that the first reference signal lags the second reference signal; and

resetting the phase detector if the second control signal is active at a falling edge of the second reference signal.

9. A method of driving an oscillating member using a phase locked loop, comprising:

applying a drive signal having a drive frequency to the oscillating member;

providing a reference signal indicative of the phase shift imparted on the drive signal by the oscillating member;

comparing the phase of the drive signal to the reference signal in a phase detector;

generating a first control signal if the reference signal lags the drive signal; and

determining whether the duty cycle of the first control signal exceeds a predetermined percent; and

increasing the frequency of the drive signal if the duty cycle of the first control signal exceeds the predetermined percent.

10. The method of claim 9, wherein the predetermined percent is at least 25 percent.

11. The method of claim 9, wherein the predetermined percent is at least 50 percent.

12. The method of claim 9, wherein the predetermined percent is at least 75 percent.

13. The method of claim 9 wherein determining whether the duty cycle of the first control signal exceeds a predetermined percent comprises determining whether the duty cycle of the first control signal exceeds a predetermined percent for at least a predetermined number of cycles of the drive signal, the predetermined number of cycles of the drive signal being at least two.

14. The method of claim 13 wherein the predetermined number of cycles of the drive signal is at least three cycles.

15. A method of driving an oscillating member using a driver, wherein the driver provides a drive signal to the oscillating member, the drive signal having a drive frequency, the method comprising:

determining whether the oscillating member is oscillating above a desired frequency;

determining whether the driver is increasing the drive frequency; and

resetting the driver if the oscillating member is oscillating above a desired frequency and the driver increasing the drive frequency.

16. A method of driving an oscillating member using a driver, wherein the driver provides a drive signal to the oscillating member, the drive signal having a drive frequency, the method comprising:

determining whether the oscillating member is oscillating below a desired frequency;

determining whether the driver is decreasing the drive frequency; and

resetting the driver if the oscillating member is oscillating above a desired frequency and the driver decreasing the drive frequency.

17. A circuit for driving an oscillating member, comprising:

a variable-frequency oscillator having an oscillator output;

an arrival-time detector having a first arrival-time detector input and a second arrival-time detector input, an up output and a down output, and a reset input, the first arrival-time detector input coupled to the oscillator output;

a phase shifter having an phase shifter input and a phase shifter output, the phase shifter input coupled to the oscillator output;

an oscillating member having a member input and a member output, the member input coupled to the phase shifter output, and the member output coupled to the second arrival-time detector input;

an error detector having a first error detector input coupled to the up output of the arrival-time detector, and a second error detector input coupled to the down output of the arrival-time detector, and an error detector output coupled to the reset input of the arrival-time detector.

18. A method of driving an oscillating member using a phase locked loop, the method comprising:

applying a drive signal having a drive frequency to the oscillating member;

providing a first reference signal to a phase detector, the first reference signal indicative of the phase shift imparted on the drive signal by the oscillating member;

providing a second reference signal to the phase detector, the second signal having the same frequency as the drive signal, but leading the drive signal by ninety degrees;

generating a first control signal if a phase detector determines that the first reference signal leads the second reference signal, and generating a second control signal if a phase detector determines that the first reference signal lags the second reference signal; and

transposing at least one of the first control signal and the second control signal is active at a falling edge of the drive signal.

19. A method of driving an oscillating member using a phase locked loop according to claim 18, wherein applying a drive signal comprises:

generating the second reference signal; and

producing the drive signal by imposing a phase shift of negative ninety degrees on the second reference signal,

such that the second reference signal leads the drive signal by 90 degrees.

20. A method of driving an oscillating member using a phase locked loop according to claim 18, wherein providing a second reference signal comprises:

generating the drive signal; and

producing the second reference signal by imposing a phase shift of 270 degrees on the reference signal,

such that the second reference signal leads the drive signal by 90 degrees.