MEMS DEVICE FRONT-END CHARGE AMPLIFIER

• US 20130263665A1
• Filed: 04/05/2013
• Published: 10/10/2013
• Est. Priority Date: 04/05/2012
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Opris, Ion, Tao, Hai, Lee, Shungneng
• Granted Patent: US 9,444,404 B2
• Time in Patent Office: Days
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719
• CPC Class Codes: H02N 1/00 Electrostatic generators or motors using a solid moving electrostatic charge carrier
• CPC Class Codes: H03F 1/00 Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 2200/294 the amplifier being a low noise amplifier [LNA]
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/70 Charge amplifiers

Abstract

This document discusses, among other things, apparatus and methods for a front-end charge amplifier. In certain examples, a front-end charge amplifier for a microelectromechanical system (MEMS) device can include a charge amplifier configured to couple to the MEMS device and to provide sense information of a proof mass of the MEMS device, a feedback circuit configured to receive the sense information and to provide feedback to an input of the charge amplifier, and wherein the charge amplifier includes a transfer function having a first pole at a first frequency, a second pole at a second frequency, and one zero at a third frequency.

Claims

1. An apparatus comprising:

a charge amplifier configured to couple to a microelectromechanical system (MEMS) device and to provide sense information of a proof mass of the MEMS device;

a feedback circuit configured to receive the sense information and to provide feedback to an input of the charge amplifier; and

wherein the charge amplifier includes a transfer function having a first pole at a first frequency, a second pole at a second frequency, and one zero at a third frequency.

2. The apparatus of claim 1, wherein the first frequency and the second frequency are at or below a resonance frequency of the proof mass.

3. The apparatus of claim 1, wherein the third frequency is substantially higher than the first frequency and the second frequency.

4. The apparatus of claim 1, wherein the two poles and the zero are configured to reduce phase offset of the sense information to substantially zero over a predetermined frequency range.

5. The apparatus of claim 1, wherein the charge amplifier include a multistage charge amplifier.

6. The apparatus of claim 5, wherein the multistage charge amplifier includes a first amplifier stage configured to provide a fixed gain.

7. The apparatus of claim 6, wherein the multistage charge amplifier includes a second amplifier stage having a transfer function including the first pole.

8. The apparatus of claim 7, wherein a gain of the second amplifier stage is a variable gain.

9. The apparatus of claim 7, wherein the multistage charge amplifier includes a third amplifier stage having a transfer function including the second pole and the zero.

10. The apparatus of claim 1, wherein the feedback circuit includes an adjustable capacitance.

11. The apparatus of claim 1, wherein the feedback circuit includes a resistor network, the resistor network including:

a current mirror coupled to the input of the charge amplifier

a first feedback resistor coupled to an output of the charge amplifier and coupled in series with the current mirror to the input of the charge amplifier; and

a second feedback resistor having a first terminal coupled to a voltage supply and a second terminal coupled to the current mirror and the first feedback resistor.

12. The apparatus of claim 1, wherein the feedback circuit includes;

a current attenuator coupled to the input of the charge amplifier; and

a transconductor coupled to the current attenuator and an output of the charge amplifier, the transconductor configured provide a current signal representative of the sense information.

13. A method comprising:

receiving a sense signal from a microelectromechanical system (MEMS) device; and

providing a voltage representative of a capacitance of the MEMS device using the sense signal and an amplifier having a first transfer function pole at a first frequency, a second transfer function pole at a second frequency, and one transfer function zero at a third frequency.

14. The method of claim 13, wherein the receiving a sense signal includes receiving a sense signal associated with a proof mass of the MEMS device;

and

wherein the first frequency and the second frequency are below or about equal to a resonance frequency of the proof mass.

15. The method of claim 13, wherein providing a voltage representative of the capacitance includes providing substantially zero phase offset over a predetermined frequency range between the sense signal and the voltage using the two transfer function poles and the transfer function zero.

16. The method of claim 14, including providing first feedback to an input of the amplifier using an adjustable capacitance coupled to an output of the amplifier.

17. The method of claim 16, including providing second feedback to the input of the amplifier using a current signal representative of the sense information.

18. The method of claim 17, wherein the providing the second feedback includes:

converting the sense information from a voltage signal to a current signal using a transconductor; and

attenuating the current signal using a current attenuator to provide the second feedback to the input.

19. A system comprising:

a microelectromechanical system (MEMS) sensor; and

a front-end charge amplifier configured to provide sense information of the MEMS sensor, the front-end charge amplifier comprising;

a charge amplifier configured to couple to the MEMS sensor and to provide the sense information of a proof mass of the MEMS sensor;

a feedback circuit configured to receive the sense information and to provide feedback to an input of the charge amplifier; and

wherein the charge amplifier includes a transfer function having a first pole at a first frequency, a second pole at a second frequency, and one zero at a third frequency.

20. The system of claim 19, wherein the MEMS sensor includes a MEMS gyroscope.