Sensor having an off-frequency drive scheme and a sense bias generator utilizing tuned circuits

• US 5,703,292 A
• Filed: 04/19/1995
• Issued: 12/30/1997
• Est. Priority Date: 03/28/1994
• Status: Expired due to Term

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Ward, Paul A.
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): Noori, Max H.
• Application Number:
  US08/425,960
• Time in Patent Office: 986 Days
• Field of Search: 73/503.3, 73/504.02, 73/504.03, 73/504.08, 73/504.16, 73/504.18
• US Class Current: 73/504.02
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: H03F 1/083 in transistor amplifiers H03F1/10 - H03F1/22 take precedence

Abstract

Electronics for use in Coriolis and other sensors for reducing errors in the sensor output signal. The electronics includes an off-frequency drive scheme for reducing in-band drive signal coupling to the output signal and techniques for reducing errors in the sensor output signal due to quadrature and phase shift. The off-frequency drive scheme includes a frequency translation circuit in the excitation feedback loop of a sensor system to suppress components of the sensor drive signal at a predetermined frequency so that coupling of the drive signal to the sensor output signal can be readily removed by conventional filtering techniques. The sensor system includes a nonlinear input transducer for converting the drive signal to a force signal such that the force signal has a component at the predetermined frequency while the drive signal does not. A tuned circuit amplifies and filters the frequency shifted output signal of the translation circuit to provide the drive signal. Also provided is a sense bias generator including a tuned circuit for amplifying the available bias supply voltage to enhance sensitivity.

Claims

1. A sensor system comprising:

an input transducer receiving a drive signal and converting said drive signal into a force signal having a non-linear relationship with respect to said drive signal;

a sensor responsive to said force signal and an external stimulus for providing a first sensor output signal having a predetermined frequency and being indicative of said force signal and a second sensor output signal having said predetermined frequency and being indicative of said external stimulus;

a frequency translation circuit responsive to said first sensor output signal for suppressing a component of said first sensor output signal at said predetermined frequency to provide a frequency translated signal capable of producing a force at said predetermined frequency; and

a tuned circuit responsive to said frequency translated signal for generating said drive signal, wherein said tuned circuit comprises an inductor and a capacitor for amplifying said frequency translated signal, so as to increase the amplitude of said drive signal.

2. The sensor system recited in claim 1 further comprising a first output transducer for converting said first sensor output signal into a feedback signal, wherein said frequency translation circuit is responsive to said feedback signal.

3. The sensor system recited in claim 1 further comprising a second output transducer for converting said second sensor output signal into a signal indicative of said external stimulus.

4. The system recited in claim 1 wherein said force signal is proportional to the square of said drive signal.

5. The sensor system recited in claim 1 wherein said tuned circuit further comprises a resistor in series with said inductor.

6. Apparatus comprising:

a sensor having a resonant frequency;

an electrostatic element responsive to a drive signal having a second frequency for generating a force signal having a component at said resonant frequency to excite said sensor, wherein said second frequency is greater than said resonant frequency; and

a tuned circuit comprising at least one capacitor and at least one inductor for amplifying said drive signal provided to said element.

7. The apparatus recited in claim 6 wherein said electrostatic element is an electrostatic actuator and said tuned circuit amplifies a drive signal provided to said electrostatic actuator.

8. The apparatus recited in claim 6 wherein said electrostatic element is a sense electrode and said tuned circuit amplifies a sense bias voltage provided to said sense electrode.

9. A method for sensing a stimulus comprising the steps of:

generating a force signal having a first frequency by applying a drive signal having a second frequency greater than said first frequency to an electrostatic element;

electrostatically actuating a sensor subjected to said stimulus and having a resonant frequency substantially equal to said first frequency with said force signal;

detecting a response of said sensor to said stimulus; and

amplifying said drive signal with a tuned circuit comprising at least one capacitor and at least one inductor.

10. The method recited in claim 9 further comprising the step of amplifying a sense bias voltage with which said response of said sensor is detected.

11. Apparatus comprising:

an electrostatic element having an admittance; and

a tuned circuit having an admittance and comprising at least one capacitor and at least one inductor for amplifying a signal provided to said element, wherein said admittance of said electrostatic element is substantially negligible with respect to said admittance of said tuned circuit.

12. A sensor system comprising:

an actuator having an admittance and receiving a drive signal;

a sensor responsive to said actuator and to a stimulus for producing an output signal;

an electrode biased by a sense bias voltage for sensing said output signal; and

a tuned circuit for amplifying at least a selected one of said drive signal and said sense bias voltage, said tuned circuit having an admittance, wherein said admittance of said actuator is substantially negligible with respect to said admittance of said tuned circuit.