Methods and apparatus for generating a sinusoidal motor drive signal for a MEMS gyroscope

• US 6,982,538 B2
• Filed: 09/06/2002
• Issued: 01/03/2006
• Est. Priority Date: 09/06/2002
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: White, Stanley A.
• Primary Examiner(s): DUDA, RINA I
• Application Number:
  US10/236,418
• Publication Number:
  US 20040046520A1
• Time in Patent Office: 1,215 Days
• Field of Search: 318/702, 318/714, 74/5.R, 74/53.7, 74/54, 74/55, 74/56.D, 74/57
• US Class Current: 318/702
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: H03H 17/0285 Ladder or lattice filters
• CPC Class Codes: H03H 17/0294 Variable filters; Programmable filters
• CPC Class Codes: H03H 17/0416 with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing
• CPC Class Codes: H03H 17/0444 where the output-delivery frequency is higher than the input sampling frequency, i.e. interpolation
• CPC Class Codes: Y10T 74/12 Gyroscopes
• CPC Class Codes: Y10T 74/1225 with rotor drives
• CPC Class Codes: Y10T 74/1229 Gyroscope control
• CPC Class Codes: Y10T 74/1257 Damping
• CPC Class Codes: Y10T 74/1275 Electrical
• CPC Class Codes: Y10T 74/1282 with rotor drive

Abstract

An apparatus is described which reduces a time delay and a resultant phase shift in a gyroscope motor drive signal. The motor drive signal originates from a numerically controlled oscillator whose output is sampled at a predetermined rate. The apparatus includes a first element which upsamples the oscillator output signal samples and a band pass filter configured to receive an output from the first element and remove spectral components from the output of the first element. The apparatus further includes a third element which generates a tuning parameter, β′_o, for tuning of the band pass filter and a scaling multiplier configured to normalize an output of the filter.

Claims

1. An apparatus to reduce a time delay and a resultant phase shift in a gyroscope motor drive signal, the motor drive signal originating from a numerically controlled oscillator having an output, the oscillator output being sampled at a predetermined rate, said apparatus comprising:

a first element which upsamples the oscillator output samples;

a band pass filter configured to receive an output from said first element and remove spectral components of the output of said first element;

a third element which generates a tuning parameter, β

′

_o, to tune said band pass filter, and

a scaling multiplier configured to normalize an output of said filter.

2. An apparatus according to claim 1 wherein said first element is configured to upsample the oscillator output by a factor of I by placing I−

1 values of zero samples between each pair of samples received from the oscillator, where I is an integer.

3. An apparatus according to claim 1 wherein I is an integer greater than one.

4. An apparatus according to claim 1 wherein I is an integer from eight to sixteen.

5. An apparatus according to claim 1 wherein said band pass filter comprises a Gray-Markel lattice-based, second order band pass interpolation filter, clocked at a frequency of I/T, where 1/T is a clock rate of the oscillator, and I is an integer.

6. An apparatus according to claim 5 wherein said band pass filter comprises an input parameter α

, for determining a bandwidth for said band pass filter, where α

has a nominal value of 0.999.

7. An apparatus according to claim 5 wherein said band pass filter comprises an input parameter a which is determined as α

=tan(π

f_BWT/I), and where f_BW is a 3 dB bandwidth (in Hz) of the pass band, 1/T is a clock rate of the oscillator, and I is an integer.

8. An apparatus according to claim 5 wherein a tuning parameter for the pass band of said filter is ${\beta }_{}^{}$

o′

=cos⁡

(2⁢

π

⁢

 

⁢

fo⁢

T/I)=cos⁡

[1I⁢

cos-1⁡

(β

o)],

where β

_o is an input to the oscillator, 1/T is a clock rate of the oscillator, I is an integer, and f₀ is a fundamental frequency.

9. An apparatus according to claim 1 wherein the tuning parameter, β

′

_o, is set to β

′

_o≈

α

₀+α

₁β

_o²+α

₂β

_o⁴, where the term β

₀², is provided by the oscillator, and α

₀, α

₁, and α

₂ are calculated coefficients.

10. An apparatus according to claim 1 wherein said scaling multiplier has a value of I/2, where I is an integer.

11. A method for reducing a time delay and a resultant phase shift in a gyroscope motor drive signal which originates from a numerically controlled oscillator, said method comprising:

placing I−

1 zero value samples between each pair of oscillator output samples, I being an integer;

filtering spectral components from the combined oscillator output samples and zero value samples;

generating a tuning parameter, β

′

_o, for said filtering; and

scaling an output of said filtering.

12. A method according to claim 11 wherein I is an integer greater than one.

13. A method according to claim 11 wherein I is an integer from eight to sixteen.

14. A method according to claim 11 wherein said filtering comprises filtering with a Gray-Markel lattice-based, second order band pass interpolation filter, clocked at a frequency of I/T, where 1/T is a clock rate of the oscillator, and I is an integer.

15. A method according to claim 14 further comprising:

providing an input parameter, α

, to the filter which has a nominal value of 0.999; and

determining a bandwidth for the band pass filter using the input parameter.

16. A method according to claim 14 further comprising providing an input parameter, α

, to the filter which is determined as α

=tan(π

f_BWT/I), and where f_BW is a 3 dB bandwidth (in Hz) of the pass band, 1/T is a clock rate of the oscillator, and I is an integer.

17. A method according to claim 14 further comprising providing a tuning parameter for the pass band of the band pass filter, the tuning parameter calculated as ${\beta }_{}^{}$

o′

=cos⁡

(2⁢

π

⁢

 

⁢

fo⁢

T/I)=cos⁡

[1I⁢

cos-1⁡

(β

o)],

where β

_o is an input to the oscillator, and f₀ is a fundamental frequency, 1/T is a clock rate of the oscillator, and I is an integer.

18. A method according to claim 14 further comprising determining the tuning parameter, β

′

_o, using a power series, where β

′

_o≈

α

₀+α

₁β

_o²+α

₂β

_o⁴, where the term β

₀², is provided by the oscillator, and α

₀, α

₁, and α

₂ are calculated coefficients.

19. A method according to claim 11 wherein said scaling an output of said filtering comprises providing a scaling multiplier with a value of I/2, where I is an integer.

20. An angular rate measurement system comprising:

a gyroscope configured to sense an angular rate input and provide a modulated angular rate information signal and a sinusoidal demodulation reference signal;

a numerically controlled oscillator (NCO) configured to receive as an input a tuning parameter β

, which is a digitized signal derived from the sinusoidal demodulation reference signal, said oscillator further configured to provide output samples;

an automatic gain control (AGC) circuit configured to amplify the output samples of said NCO;

an interpolator configured to place I−

1 zero value samples between each pair of amplified output samples, said interpolator comprising a filter configured to filter extraneous spectral components from the combined amplified output samples and zero value samples, generate a tuning parameter, β

′

_o, for said filter, and scale the filtered samples to be output from said interpolator, where I is an integer; and

a digital-to-analog converter and filter, said converter and filter configured to produce a motor drive signal from an output of said interpolator.

21. An angular rate measurement system according to claim 20 wherein I is an integer ranging from eight to sixteen.

22. An angular rate measurement system according to claim 20 wherein said interpolator comprises a Gray-Markel lattice-based, second order band pass interpolation filter, clocked at a frequency of I/T, where 1/T is a clock rate of said NCO and I is an integer.

23. An angular rate measurement system according to claim 20 wherein an input parameter to said interpolator, α

, is determined according to α

=tan(π

f_BWT/I), and where f_BW is a 3 dB bandwidth (in Hz) of a pass band for said filter, where 1/T is a clock rate of said NCO, 1/T is a clock rate of the oscillator, and I is an integer.

24. An angular rate measurement system according to claim 20 wherein a tuning parameter for a pass band for said filter is calculated as ${\beta }_{}^{}$

o′

=cos⁡

(2⁢

π

⁢

 

⁢

fo⁢

T/I)=cos⁡

[1I⁢

cos-1⁡

(β

o)],

where β

_o is an input to said NCO, f₀ is a fundamental frequency, 1/T is a clock rate of the oscillator, and I is an integer.

25. An angular rate measurement system according to claim 20 wherein said interpolator is configured to approximate a tuning parameter, β

′

_o, for said filter using a power series, where β

′

_o≈

α

₀+α

₁β

_o²+α

₂β

_o⁴, where the term β

₀², is provided by said oscillator, and α

₀, α

₁, and α

₂ are calculated coefficients.

26. An angular rate measurement system according to claim 25 wherein α

₀ is 0.9967032511, α

₁ is 0.00526891, and α

₂ is −

0.0021640344.