Electronics for Coriolis force and other sensors

• US 5,672,949 A
• Filed: 05/24/1995
• Issued: 09/30/1997
• 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
• Primary Examiner(s): IP, SHIK LUEN PAUL
• Application Number:
  US08/449,020
• Time in Patent Office: 860 Days
• Field of Search: 318/560-696, 318/490, 244/3.17, 244/3.11, 364/570, 364/565, 364/484, 364/481, 364/480, 364/485, 329/307, 329/325, 329/341, 329/343, 329/356, 329/360, 331/27, 331/60, 367/135, 367/901, 73/1 D, 73/517 A, 73/517 AV, 73/517 R, 73/505, 73/504, 375/327, 375/328, 375/376
• US Class Current: 318/609
• 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. An 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. An amplifier circuit having a bandpass circuit in cascade with the forward loop gain is provided, with the bandpass circuit having a transfer function approximating one plus a bandpass characteristic, the passband of which corresponds to the information band. This arrangement increases the open-loop gain of the amplifier circuit around the information frequency without affecting the open-loop gain at DC and crossover so as to reduce phase and gain errors around the information frequency. A quadrature nulling system is provided for an in-plane micromechanical gyroscope. A signal having an in-phase component due to Coriolis induced out-of-plane motion and a quadrature component due to mechanical misalignments is mixed with a voltage in-phase with motor position. The mixer output is used to apply a DC potential to motor drive electrodes and is automatically adjusted by the integral compensator until the mixer output is zero, resulting in a nulled quadrature component.

Claims

1. A negative feedback servo system having an input and an output and being responsive to information at an information frequency, said servo system comprising:

a forward gain stage coupled between said input and said output of said servo system and having an open-loop gain; and

a bandpass circuit having an input and an output and a transfer function relating said output to said input, said transfer function comprising a bandpass characteristic substantially centered at said information frequency, wherein said bandpass circuit is disposed in cascade with said forward gain stage, between said input and said output of said servo system.

2. The servo system recited in claim 1 wherein said transfer function of said bandpass circuit approximates one plus said bandpass characteristic.

3. The servo system recited in claim 1 wherein said forward gain stage comprises:

a first operational amplifier having a gain and being disposed in cascade with said bandpass circuit; and

a feedback network coupled between said output of said bandpass circuit and an input of said first operational amplifier.

4. The servo system recited in claim 3 wherein said bandpass circuit has a resonance frequency corresponding to said information frequency and an open-loop gain and said servo system has a composite open-loop gain proportional to the sum of said open-loop gain of said forward gain stage and said open-loop gain of said bandpass circuit, and wherein said bandpass circuit comprises two parallel signal paths, a first one of said signal paths having a gain substantially independent of frequency and dominating said open-loop gain of said bandpass circuit at frequency extremes so that said composite open-loop gain of said servo system is governed by said gain of said first operational amplifier at said frequency extremes, and a second one of said signal paths having a frequency dependent gain dominating said open-loop gain of said bandpass circuit at said resonance frequency so that said composite open-loop gain of said servo system is governed by said open-loop gain of said bandpass circuit at said resonance frequency.

5. The servo system recited in claim 3 wherein said bandpass circuit comprises:

a second operational amplifier having a non-inverting input coupled to an output of said first operational amplifier, an output providing said output of said bandpass circuit; and

a feedback network coupled between said output of said bandpass circuit and an inverting input of said second operational amplifier, wherein said feedback network provides said transfer function of said bandpass circuit.

6. A servo system comprising:

a first operational amplifier having a gain;

a bandpass circuit having a resonance frequency and an open-loop gain, wherein said servo system has a composite open-loop gain proportional to the sum of said gain of said first operational amplifier and said open-loop gain of the bandpass circuit, said bandpass circuit disposed in cascade with said first operational amplifier and comprising two parallel signal paths, a first one of said signal paths having a gain substantially independent of frequency and dominating said open-loop gain of said bandpass circuit at frequency extremes so that said composite open-loop gain of said servo system is governed by said gain of said first operational amplifier at said frequency extremes, and a second one of said signal paths having a frequency dependent gain dominating said open-loop gain of said bandpass circuit at said resonance frequency so that said composite open-loop gain of said servo system is governed by said open-loop gain of said bandpass circuit at said resonance frequency; and

a feedback network coupled between an input of said first operational amplifier and an output of said bandpass circuit.