MEMS device automatic-gain control loop for mechanical amplitude drive

• US 9,618,361 B2
• Filed: 04/05/2013
• Issued: 04/11/2017
• Est. Priority Date: 04/05/2012
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Opris, Ion, Tao, Hai, Lee, Shungneng
• Primary Examiner(s): Chapman, Jr., John
• Application Number:
  US13/857,363
• Publication Number:
  US 20130268227A1
• Time in Patent Office: 1,467 Days
• CPC Class Codes: G01C 19/5726 Signal processing
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

This document discusses, among other things, apparatus and methods for digital automatic gain control for driving a MEMS device, such as a proof mass. In an example, an apparatus can include a driver configured to oscillate a proof mass of a MEMS device, a charge-to-voltage (C2V) converter configured to provide oscillation information of the proof mass, an analog-to-digital converter (ADC) configured to provide a digital representation of the oscillation information, and a digital, automatic gain control circuit to provide oscillation amplitude error information using a comparison of the oscillation information to target amplitude information, and to provide a digital drive command signal using an amplified representation of the oscillation amplitude error information.

Claims

1. An apparatus comprising:

a driver configured to oscillate a proof mass of a MEMS gyroscope;

a charge-to-voltage (C2V) converter configured to receive a sense signal from a MEMS gyroscope and to provide oscillation information of the proof mass;

an analog-to-digital converter (ADC) configured to receive the oscillation information of the proof mass and to provide a digital representation of the oscillation information; and

a digital, automatic gain control circuit configured to receive the digital representation of the oscillation information, to provide oscillation amplitude error information using a comparison of the oscillation information to target amplitude information, and to provide a digital drive command signal using an amplified representation of the oscillation amplitude error information, the digital, automatic gain control circuit includes an output stage, the output stage including;

a fine gain register configured to provide a basic unit of change of the digital drive command signal;

a low pass filter; and

a coarse gain counter configured to increment on overshoot of the fine gain register, to decrement on undershoot of the fine gain register, and to provide a correction to the amplified representation of the oscillation amplitude error information.

2. The apparatus of claim 1, wherein the ADC is configured to provide the digital representation of the sense signal using a single-bit data stream.

3. The apparatus of claim 2, wherein the digital, automatic gain control circuit includes a down-sample module to receive the single-bit data stream and provide a second digital representation of the sense signal using a first multi-bit data stream.

4. The apparatus of claim 3, wherein the digital, automatic gain control circuit includes a band pass filter configured to receive the first multi-bit data stream and provide a third digital representation of the sense signal using a second multi-bit data stream.

5. The apparatus of claim 4, wherein the digital, automatic gain control circuit includes an amplitude detector configured to perform a square operation of the third digital representation of the sense signal to provide amplitude information of the sense signal.

6. The apparatus of claim 4, wherein the digital, automatic gain control circuit includes a digital comparator configured to receive amplitude information and the target information and to provide the oscillation amplitude error information.

7. The apparatus of claim 6, wherein the digital, automatic gain control circuit includes a finite impulse response filter configured to average the oscillation amplitude error information over a plurality of sample periods to provide a smoothed error signal.

8. The apparatus of claim 1, wherein the ADC includes a band-pass, delta-sigma ADC.

9. The apparatus of claim 1, including a digital-to-analog converter configured to receive at least a portion of the digital drive command signal and to provide an analog command signal to the driver.

10. A method comprising:

oscillating a proof mass of a MEMS gyroscope using a driver;

receiving oscillation information of the proof mass using a charge-to-voltage converter;

providing a digital representation of the oscillation information using an analog to digital converter;

providing oscillation amplitude error information using a comparison of the oscillation information to target amplitude information, and a digital automatic gain control circuit;

providing a digital drive command signal using the oscillation amplitude error information and the digital automatic gain control circuit;

receiving an amplified representation of the oscillation amplitude error information at an output stage of the digital automatic gain control circuit;

processing the amplified representation of the oscillation amplitude error information using a digital limiter and one or more digital up-samplers to provide a fine portion of the digital drive command signal; and

processing the amplified representation of the oscillation amplitude error information using a low pass filter and a gain control counter to provide a coarse portion of the digital drive command signal.

11. The method of claim 10, wherein providing a digital representation includes providing a digital representation of the oscillation information using a using a single-bit data stream.

12. The method of claim 11, including down-sampling the single-bit data stream to provide a second digital representation of the oscillation information using a multi-bit data stream.

13. The method of claim 12, including processing the first multi-bit data stream using a band-pass filter to provide a third digital representation of the oscillation information.

14. The method of claim 13, including:

receiving the third digital representation of the oscillation information at a amplitude detector of the digital automatic gain control circuit; and

providing amplitude information of the oscillation information using the amplitude detector.

15. The method of claim 14, including comparing the amplitude information to the target information to provide the oscillation amplitude error information using a digital comparator of the digital automatic gain control circuit.

16. The method of claim 15, including averaging the oscillation amplitude error information over a predetermined number of samples using a finite impulse response filter to provide a smoothed error signal.

17. The method of claim 10, including converting the digital, drive command signal to an analog, drive command signal using an digital-to-analog converter;

and

receiving the analog command signal at the driver.

18. The method of claim 10, wherein processing the amplified representation of the oscillation amplitude error information using a low pass filter and a gain control counter includes incrementing the gain control counter when the low pass filter overshoots;

and

decrementing the gain control counter when the low pass filter undershoots.

19. The method of claim 10, wherein processing the amplified representation of the oscillation amplitude error information using a low pass filter and a gain control counter includes feeding back a correction to the amplified representation of the oscillation amplitude error information when a value of the gain control counter changes.