Method and apparatus for synchronous demodulation of multiply modulated signals

• US 6,714,025 B2
• Filed: 02/19/2002
• Issued: 03/30/2004
• Est. Priority Date: 02/17/2001
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Bauer, Wolfram, Mohaupt, Jens
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): Dole, Timothy J.
• Application Number:
  US10/079,765
• Publication Number:
  US 20020125940A1
• Time in Patent Office: 770 Days
• Field of Search: 324/681, 324/682, 324/686, 329/315, 735/040.2, 735/040.3
• US Class Current: 324/681
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces

Abstract

A method and an apparatus for synchronous demodulation of the multiply modulated rotation rate signal of a rotation rate sensor which comprises a spring-mass system that oscillates at its natural resonant frequency, and at least one capacitor for ascertaining a Coriolis effect acting on the spring-mass system or a rotation rate, the rotation rate being ascertained by a time-variable capacitance change, brought about by the rotation rate, of the at least one capacitor by multiple demodulation of a multiply modulated electrical signal that comprises a time-variable first electrical signal and a second electrical signal, overlaid thereon, at the natural resonant frequency of the rotation rate sensor, the amplitude of the second electrical signal of the time-variable capacitance change of the at least one capacitor being correspondingly modulated. To substantially reduce the outlay for synchronous demodulation, the first electrical signal is generated so that it exhibits a time-invariant phase relationship to the natural resonant frequency of the rotation rate sensor.

Claims

1. A method to synchronously demodulate a multiply modulated rotation rate signal of a rotation rate sensor having a spring-mass system that oscillates at its natural resonant frequency and at least one capacitor to ascertain a rotation rate of a Coriolis effect acting on the spring-mass system, the method comprising:

generating a time-variable first electrical signal so that it exhibits a time-invariant phase relationship to the natural resonant frequency of the rotation rate sensor;

superimposing a second electrical signal, at the natural resonant frequency of the rotation rate sensor, on the first electrical signal to provide a multiply modulated electrical signal, an amplitude of the second electrical signal of a time-variable capacitance change of the at least one capacitor being correspondingly modulated; and

ascertaining the time-variable capacitance change associated with the rotation rate and ascertaining the rotation rate by multiply demodulating a multiply modulated electric signal;

wherein;

the at least one capacitor includes two stationary capacitor electrodes and a capacitor electrode that is movable as a consequence of the action of the rotation rate;

the capacitor electrode is movable toward a first one of the two stationary capacitor electrodes and simultaneously movable away from a second one of the two stationary capacitor electrodes, the moving of the capacitor electrode bringing about two time-variable and mutually inverse capacitance changes;

the second electrical signal superimposed on the first electrical signal is modulated in accordance with the two time-variable and mutually inverse capacitance changes; and

the multiply modulated electrical signal is conveyed to a capacitance/voltage converter that delivers two mutually inverse time-variable voltage signals;

wherein in a first step, a first mutually inverse time-variable voltage signal is conveyed to a first input of a summer under a control of a first control signal, and a second mutually inverse time-variable voltage signal is conveyed to a second input of the summer under the control of the first control signal.

2. The method of claim 1, wherein the first electrical signal is generated so that a frequency of the first signal corresponds to 2ⁿ times the natural resonant frequency, where n is a positive integer.

3. The method of claim 1, wherein the at least one capacitor includes a first stationary capacitor electrode and a second capacitor moved with respect to the first capacitor electrode as a consequence of an action of the rotation rate, as a result of which a capacitance changes.

4. The method of claim 3, wherein the multiply modulated electrical signal is conveyed to a capacitance/voltage converter that delivers a time-variable voltage signal based on an amplitude modulation of the second electrical signal brought about by the time-variable capacitance of the at least one capacitor.

5. The method of claim 1, wherein in a second step, the first mutually inverse time-variable voltage signal is conveyed to the second input of the summer under the control of a second control signal, and the second mutually inverse time-variable voltage signal is conveyed to the first input of the summer under the control of the second control signal.

6. The method of claim 5, wherein the second control signal is a switch-on signal during a time period during which the first mutually inverse time-variable voltage signal exhibits a positive voltage pulse.

7. The method of claim 5, wherein the first control signal one of opens and closes two first electronic switches, and the second control signal one of opens and closes two second electronic switches.

8. The method of claim 5, wherein the first control signal and the second control signal are generated by a logic circuit to which the first electrical signal, the second electrical signal, and the two mutually inverse time-variable voltage signals are conveyed.

9. The method of claim 5, wherein the first control signal, the second control signal and the mutually inverse voltage signals are conveyed to a synchronous demodulator that includes a summer and four electronic switches controlled by the first and second control signals, the summer delivering one of a rotation rate signal reproducing the rotation rate of the rotation rate sensor and a precursor stage of the rotation rate signal.

10. The method of claim 1, wherein the first control signal is a switch-on signal during a time period during which the second mutually inverse time-variable voltage signal exhibits a positive voltage pulse.

11. The method of claim 1, wherein the first electrical signal is generated by a phase lock loop (PLL) based on the natural resonant frequency of the rotation rate sensor.

12. The method of claim 11, wherein the PLL includes a voltage controlled oscillator to generate the first electrical signal.

13. The method of claim 1, wherein the capacitance/voltage converter is a charge amplifier having switched capacitor technology.

14. An apparatus to synchronously demodulate a multiply modulated rotation rate signal of a rotation rate sensor, the apparatus comprising:

a spring-mass system that oscillates at its natural resonant frequency; and

at least one capacitor to ascertain a rotation rate of a Coriolis effect acting on the spring-mass system;

a generating arrangement to generate a time-variable first electrical signal so that it exhibits a time-invariant phase relationship to the natural resonant frequency of the rotation rate sensor;

a superimposing arrangement to superimpose a second electrical signal, at the natural resonant frequency of the rotation rate sensor, on the first electrical signal to provide a multiply modulated electrical signal, an amplitude of the second electrical signal of a time-variable capacitance change of the at least one capacitor being correspondingly modulated; and

an ascertaining arrangement to ascertain the time-variable capacitance change associated with the rotation rate and ascertaining the rotation rate by multiply demodulating a multiply modulated electric signal;

wherein;

the at least one capacitor includes two stationary capacitor electrodes and a capacitor electrode that is movable as a consequence of the action of the rotation rate;

the capacitor electrode is movable toward a first one of the two stationary capacitor electrodes and simultaneously movable away from a second one of the two stationary capacitor electrodes, the moving of the capacitor electrode bringing about two time-variable and mutually inverse capacitance changes;

the second electrical signal superimposed on the first electrical signal is modulated in accordance with the two time-variable and mutually inverse capacitance changes; and

the multiply modulated electrical signal is conveyed to a capacitance/voltage converter that delivers two mutually inverse time-variable voltage signals;

wherein a first mutually inverse time-variable voltage signal is conveyed to a first input of a summer under a control of a first control signal, and a second mutually inverse time-variable voltage signal is conveyed to a second input of the summer under the control of the first control signal.

15. The apparatus of claim 14, further comprising:

a capacitance/voltage converter to deliver at least one time-variable voltage signal;

a PLL to generate at least one electrical signal based on the natural resonant frequency of the rotation rate sensor;

a logic circuit to generate at least one control signal; and

a synchronous demodulator to demodulate the multiply modulated rotation rate signal.

16. The apparatus of claim 14, wherein the capacitance/voltage converter is a charge amplifier having switched capacitor technology.

17. The apparatus of claim 14, wherein the first mutually inverse time-variable voltage signal is conveyed to the second input of the summer under the control of a second control signal, and the second mutually inverse time-variable voltage signal is conveyed to the first input of the summer under the control of the second control signal.

18. The apparatus of claim 17, wherein the second control signal is a switch-on signal during a time period during which the first mutually inverse time-variable voltage signal exhibits a positive voltage pulse.

19. The apparatus of claim 17, wherein the first control signal one of opens and closes two first electronic switches, and the second control signal one of opens and closes two second electronic switches.

20. The apparatus of claim 17, wherein the first control signal and the second control signal are generated by a logic circuit to which the first electrical signal, the second electrical signal, and the two mutually inverse time-variable voltage signals are conveyed.

21. The apparatus of claim 17, wherein the first control signal, the second control signal and the mutually inverse voltage signals are conveyed to a synchronous demodulator that includes a summer and four electronic switches controlled by the first and second control signals, the summer delivering one of a rotation rate signal reproducing the rotation rate of the rotation rate sensor and a precursor stage of the rotation rate signal.

22. The apparatus of claim 14, wherein the first control signal is a switch-on signal during a time period during which the second mutually inverse time-variable voltage signal exhibits a positive voltage pulse.

23. The apparatus of claim 14, wherein the first electrical signal is generated by a phase lock loop (PLL) based on the natural resonant frequency of the rotation rate sensor.

24. The apparatus of claim 17, wherein the capacitance/voltage converter is a charge amplifier having switched capacitor technology.