Differential parametric amplifier with physically-coupled electrically-isolated micromachined structures

• US 6,611,168 B1
• Filed: 12/19/2001
• Issued: 08/26/2003
• Est. Priority Date: 12/19/2001
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Kelly, Thomas W., Denison, Timothy J.
• Primary Examiner(s): Mottola, Steven J.
• Application Number:
  US10/024,741
• Time in Patent Office: 615 Days
• Field of Search: 330/4.5, 330/4.9, 330/9
• US Class Current: 330/4.5
• CPC Class Codes: H01G 5/16 using variation of distance between electrodes
• CPC Class Codes: H03F 2200/261 Amplifier which being suitable for instrumentation applications
• CPC Class Codes: H03F 3/38 DC amplifiers with modulator at input and demodulator at output; Modulators or demodulators specially adapted for use in such amplifiers switched capacitor amplifiers H03F3/005
• CPC Class Codes: H03F 7/04 using variable-capacitance element; using variable-permittivity element

Abstract

A micromachined variable capacitor structure is used as a modulation mechanism for a differential parametric amplifier. The capacitance of the capacitor structure is modulated by a control signal while a differential signal is applied to the capacitor structure. Modulation of the capacitance produces a signal representative of the input differential voltage. This signal is provided to an amplifier. Once the signal is amplified, a demodulator demodulates the amplified signal to provide an amplified version of the differential signal. The variable capacitor structure also allows for internal feedback, which permits the parametric amplifier to be used as a galvanically isolated differential measurement amplifier. A number of techniques are used to remove common mode and other errors from the modulated difference signal, thereby eliminating them from the amplified output.

Claims

1. A parametric amplifier comprising:

at least a first variable capacitor structure, the first variable capacitor structure including one or more sections of oscillating capacitive elements comprising cooperating fixed and movable electrodes, the movable electrodes connected to a common center structure;

an ac amplifier operatively connected to the center structure,

a demodulator operatively connected to the ac amplifier; and

wherein the first variable capacitor structure transduces a differential input signal applied with first polarity across the capacitive elements into a modulated input signal, the ac amplifier receives the modulated input signal via the center structure and outputs an amplified modulated input signal, the demodulator receives the amplified modulated input signal and demodulates the amplified modulated input signal to output an amplified input signal.

2. A parametric amplifier, as per claim 1, wherein one or more spring motive forces and one or more electromotive forces place the common center structure in motion to oscillate the movable electrodes of the oscillating capacitive elements.

3. A parametric amplifier, as per claim 2, wherein the one or more sections comprises at least two sections:

a drive section, the drive section generating the one or more electromotive forces when one or more electrostatic forces are applied to the fixed electrodes of the drive section, and

an input sense section, the fixed electrodes of the input sense section having the differential input signal applied thereto with the first polarity.

4. A parametric amplifier, as per claim 3, wherein the input sense section has a cross-quad structure.

5. A parametric amplifier, as per claim 3, wherein

the differential input signal is a differential input voltage, the differential input voltage is transduced into an electric current corresponding to a modulated form of the differential input voltage;

the amplifier receives the electric current via the center structure and outputs an amplified electric current, and

the demodulator receives the amplified electric current and demodulates the amplified electric current to generate a demodulated electric current corresponding to an amplified form of the differential input voltage and generates an output voltage from the demodulated electric current.

6. A parametric amplifier, as per claim 3, wherein the one or more sections comprises at least four sections, additionally including:

a force feedback section, the fixed electrodes of the force feedback section providing a velocity signal to an oscillation control circuit, the velocity signal representative of a velocity of the center structure with respect to the fixed electrodes, the oscillation control circuit generating the one or more electrostatic forces applied to the fixed electrodes of the drive section based upon the velocity signal, and

an input feedback section, the fixed electrodes of the input feedback section operatively connected to an output of the demodulator.

7. A parametric amplifier, as per claim 6, wherein fixed electrodes of the input feedback section are operatively connected to the output of the demodulator via an integrator or other suitable feedback compensation circuit.

8. A parametric amplifier, as per claim 6, wherein the center structure comprises at least one isolation coupling electrically isolating the input sense section and the input feedback section from the drive section and the force feedback section.

9. A parametric amplifier, as per claim 6, wherein the one or more sections comprises a plurality of input sense sections and a ratio of input sense sections to input feedback sections is greater than one.

10. A parametric amplifier, as per claim 6, wherein the one or more sections comprises a plurality of input feedback sections and a ratio of input sense sections to input feedback sections is less than one.

11. A parametric amplifier, as per claim 1, further comprising:

a second micromachined variable capacitor structure, the second variable capacitor structure including one or more sections of capacitive elements comprising cooperating fixed and movable electrodes, the movable electrodes connected to a common center structure, the common center structure of the second variable capacitor structure operatively connected to the ac amplifier.

12. A parametric amplifier, as per claim 11, wherein

one or more spring motive forces and one or more electromotive forces place the common center structure of the first variable capacitor structure and the common center structure of the second variable capacitor structure in motion to create oscillation of the movable electrodes of the first and second variable capacitor structure;

the one or more sections of the first variable capacitor structure comprises at least two sections;

a drive section, the drive section generating the one or more electromotive forces when one or more electrostatic forces are applied to the fixed electrodes of the drive section, and an input sense section, the fixed electrodes of the input sense section having the differential input signal applied thereto with the first polarity;

the one or more sections of the second variable capacitor structure comprises at least two sections;

a drive section, the drive section generating the one or more electromotive forces when one or more electrostatic forces are applied to the fixed electrodes of the drive section, and an input sense section, the fixed electrodes of the input sense section having the differential input signal applied thereto with second polarity opposite of the first polarity, and

the common center structure of the first variable capacitor structure and the common center structure of the second variable capacitor structure are connected by an isolation coupling such that the common center structure of the first variable capacitor structure and the common center structure of the second variable capacitor structure move substantially in tandem.

13. A parametric amplifier, as per claim 1, further comprising:

a measurement capacitor structure, the measurement capacitor structure including one or more sections of oscillating capacitive elements comprising cooperating fixed and movable electrodes, the movable electrodes connected to a common center structure, the measurement capacitor structure transducing the differential input signal into a common mode correction signal representative of common mode disturbances in the differential input signal, and

wherein a proportion of the common mode correction signal is added to the modulated input signal to remove common mode disturbances from the modulated input signal.

14. A parametric amplifier, as per claim 1, wherein a capacitance of the capacitive elements is mechanically adjusted by isolating one or more of the fixed electrodes from the differential input signal.

15. A parametric amplifier, as per claim 1, wherein the parametric amplifier is used as an operational amplifier.

16. A parametric amplifier, as per claim 1, wherein the parametric amplifier is used to measure offset of a second amplifier and provide an offset correction signal to the second amplifier.

17. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, the parametric amplifier comprising:

at least a first micromachined variable capacitor structure having the differential input voltage applied across oscillating capacitive elements of the first capacitor structure to transduce the differential input voltage into a first electric current corresponding to a modulated form of the differential input voltage;

an ac amplifier receiving the first electric current and outputting an amplified electric current;

a demodulator demodulating the amplified electric current to generate a demodulated electric current corresponding to an amplified form of the differential input voltage, and

wherein the output voltage is generated from the demodulated electric current.

18. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 17, further comprising:

oscillation control circuitry, the oscillation control circuitry controlling a period of oscillation of the capacitive elements.

19. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 18, wherein the first variable capacitor structure comprises an oscillator portion and an input portion operatively connected by an electrically conductive center structure,

the oscillator portion comprising:

a first spring structure operatively connected to the center structure;

a drive section having first fixed electrically conductive fingers receiving an oscillation control signal from the oscillation control circuit, the first fixed fingers interlaced with first movable electrically conductive fingers, the first movable fingers operatively connected to the center structure;

the input portion comprising;

a second spring structure operatively connected to the center structure;

a differential voltage input sense section having second fixed electrically conductive fingers receiving the differential voltage, the second fixed fingers interlaced with second movable electrically conductive fingers, the second movable fingers operatively connected to the center structure.

20. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 19, wherein the input sense section has a cross-quad structure.

21. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 19, wherein the first movable fingers and first fixed fingers comprise:

a first set of movable, electrically conductive fingers extending in a first direction substantially parallel to the center structure and operatively connected to the center structure via an electrically conductive cross beam;

a first set of fixed electrically conductive fingers interlaced with the first set of movable fingers;

a second set of movable, electrically conductive fingers extending in a direction substantially opposite to the first direction and operatively connected to the center structure via the electrically conductive cross beam; and

a second set of fixed electrically conductive fingers interlaced with the second set of movable fingers; and

wherein the oscillation control signal comprises a first alternating voltage applied to the first set of fixed fingers and a second alternating voltage applied to the second set of fixed fingers.

22. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 19, wherein the second movable fingers and second fixed fingers comprise:

a first set of movable, electrically conductive fingers extending in a first direction substantially parallel to the center structure and operatively connected to the center structure via a electrically conductive cross beam;

a first set of fixed electrically conductive fingers interlaced with the first set of movable fingers, the first set of fixed fingers receiving a first electric potential of the differential voltage;

a second set of movable, electrically conductive fingers extending in a direction substantially opposite to the first direction and operatively connected to the center structure via the electrically conductive cross beam; and

a second set of fixed electrically conductive fingers interlaced with the second set of movable fingers, the second set of fixed fingers receiving a second electric potential of the differential voltage.

23. A macrofabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 22, wherein at least one of the first set of fixed fingers is isolated from the first electric potential.

24. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 19, the oscillator portion further comprising:

a velocity feedback section having third fixed electrically conductive fingers providing a velocity feedback signal to the oscillation control circuit, the velocity feedback signal representative of a velocity of third movable electrically conductive fingers interlaced with the third fixed fingers, the third movable fingers operatively connected to the center structure.

25. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 24, wherein

the third movable fingers comprise:

a first set of movable, electrically conductive fingers extending in a first direction substantially parallel to the center structure and operatively connected to the center structure via a electrically conductive cross beam;

a second set of movable, electrically conductive fingers extending in a direction substantially opposite to the first direction and operatively connected to the center structure via the electrically conductive cross beam;

the third fixed fingers comprise;

a first set of fixed electrically conductive fingers interlaced with the first set of movable fingers;

a second set of fixed electrically conductive fingers interlaced with the second set of movable fingers, and

wherein the velocity feedback signal comprises a first voltage output by the first fixed fingers and a second voltage output by the second fixed fingers.

26. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 25, wherein the oscillation control circuit comprises:

a feedback ac amplifier receiving the velocity feedback signal as the first voltage and the second voltage and outputting an amplified velocity feedback signal as an amplified first voltage and an amplified second voltage;

a comparator comparing the amplified first voltage and the second amplified voltage and outputting a first compare signal and a second compare signal based upon the comparison;

a force feedback conditioner conditioning the first compare signal and the second compare signal and outputting the conditioned first compare signal and the conditioned second compare signal as the oscillation control signal.

27. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 26, the oscillation control circuit further comprising:

a signal limiter receiving the amplified velocity feedback signal and a reference voltage indicative of a maximum magnitude of the oscillation control signal and outputting a limiting signal to the feedback conditioner causing the feedback conditioner to limit a magnitude of the first compare signal and a magnitude of the second compare signal.

28. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 19, the input portion further comprising:

an input feedback section having third fixed electrically conductive fingers receiving the output voltage, the third fixed fingers interlaced with third movable electrically conductive fingers, the third movable fingers operatively connected to the center structure.

29. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 28, wherein the output voltage is generated by an integrator or other suitable feedback compensation circuit receiving the demodulated electric current.

30. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 28, wherein

the third movable fingers comprise:

a first set of movable, electrically conductive fingers extending in a first direction substantially parallel to the first center structure and operatively connected to the center structure via a electrically conductive cross beam;

a second set of movable, electrically conductive fingers extending in a direction substantially opposite to the first direction and operatively connected to the center structure via the electrically conductive cross beam;

the third fixed fingers comprise;

a first set of fixed electrically conductive fingers interlaced with the first set of movable fingers, and

a second set of fixed electrically conductive fingers interlaced with the second set of movable fingers.

31. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 19, wherein the center structure comprises an isolation coupling, the isolation coupling electrically isolating the oscillator portion from the input portion.

32. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 31, further comprising:

a second micromachined variable capacitor structure having the differential input voltage applied across oscillating capacitive elements of the second capacitor structure to transduce the differential input voltage into a second electric current corresponding to a modulated form of the differential input voltage, the second variable capacitor structure comprising an oscillator portion and an input portion operatively connected by an electrically conductive center structure,

the oscillator portion of the second capacitor structure comprising;

a first spring structure operatively connected to the center structure;

a drive section having first fixed electrically conductive fingers receiving an oscillation control signal from the oscillation control circuit, the first fixed fingers interlaced with first movable electrically conductive fingers, the first movable fingers operatively connected to the center structure;

the input portion of the second capacitor structure comprising;

a second spring structure operatively connected to the center structure;

a differential voltage input sense section having second fixed electrically conductive fingers receiving the differential voltage, the second fixed fingers interlaced with second movable electrically conductive fingers, the second movable fingers operatively connected to the center structure, and

wherein the center structure of the second capacitor structure comprises an isolation coupling electrically isolating the oscillation portion of the second capacitor structure from the input portion of the second capacitor structure, the first capacitor structure and the second capacitor structure operatively connected via the isolation couplings, the differential voltage is applied across oscillating capacitive elements of the second capacitor structure with opposite polarity than as applied across oscillating capacitive elements of the second capacitor, the ac amplifier is a differential amplifier receiving both the first electric current and the second electric current and outputting an amplified electric current having reduced common mode disturbances.

33. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 19, further comprising

a measurement variable capacitor structure having the differential input voltage applied across oscillating capacitive elements of the second capacitor structure to transduce the differential input voltage into a second electric current representing common mode disturbances in the first electric current, and

wherein a proportion of the second electric current is summed with the first electric current to remove the common mode disturbances.

34. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 17, wherein the parametric amplifier is used as an operational amplifier.

35. A microfabricated parametric amplifier for generating an output voltage by amplifying a differential input voltage, as per claim 17, wherein the parametric amplifier is used to measure offset of a second amplifier and provide an offset correction signal to the second amplifier.