Semiconductor Device and Method of Direct Measurement and Acquisition of MEMS Employing Sigma-Delta Loop

• US 20140266251A1
• Filed: 01/21/2014
• Published: 09/18/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Semtech Corporation
• Original Assignee: Semtech Corporation
• Inventors: Chevroulet, Michel, Nys, Olivier
• Granted Patent: US 9,574,907 B2
• Time in Patent Office: Days
• US Class Current: 324/661
• CPC Class Codes: G01D 5/24 by varying capacitance

Abstract

A semiconductor device measures a state of a MEMS as a first voltage variation at a sensing node. The state of the MEMS includes a capacitance. A first capacitor is coupled between the sensing node and an input of an integrator for transferring the first voltage variation to a second node as a first signal. A second voltage variation is routed through a second capacitor to the second node as a second signal. The integrator integrates the first signal and second signal to provide an integrated signal. An ADC has an input coupled to an output of the integrator and converts the integrated signal to a digital signal representative of the capacitance of the MEMS. A DAC has an input coupled to the output of the ADC. A second capacitor is coupled between an output of the DAC and the sensing node.

Claims

1. A measurement circuit for a microelectromechanical system (MEMS), comprising:

a sensing node for measuring a state of the MEMS;

an integrator;

a first capacitor coupled between the sensing node and an input of the integrator;

an analog-to-digital converter (ADC) including an input coupled to an output of the integrator and an output providing a digital signal representative of the state of the MEMS;

a digital-to-analog converter (DAC) including an input coupled to the output of the ADC; and

a second capacitor coupled between an output of the DAC and the sensing node.

2. The measurement circuit of claim 1, wherein the MEMS includes a capacitance and the digital signal at the output of the ADC is representative of the capacitance of the MEMS.

3. The measurement circuit of claim 1, further including:

a modulator including a first input coupled for receiving a reference voltage and a second input coupled for receiving a modulating signal;

a demodulator including a first input coupled to the first capacitor, second input coupled for receiving a demodulating signal, and an output coupled to the input of the integrator; and

a third capacitor coupled between an output of the first modulator and the first input of the second modulator.

4. The measurement circuit of claim 1, further including a modulator comprising a first input coupled to the output of the DAC and a second input coupled for receiving a modulating signal with the second capacitor coupled between an output of the modulator and the sensing node.

5. The measurement circuit of claim 1, further including a charge pump coupled to the sensing node.

6. The measurement circuit of claim 1, further including a semiconductor package containing the measurement circuit with a pin of the semiconductor package coupled to the sensing node.

7. A method of measuring a microelectromechanical system (MEMS), comprising:

sensing a state of the MEMS as a first voltage variation at a sensing node;

transferring the first voltage variation through a first capacitor to a second node as a first signal;

providing a second voltage variation through a second capacitor to the second node as a second signal;

integrating the first signal and second signal to provide an integrated signal;

converting the integrated signal to a digital signal representative of the state of the MEMS;

converting the digital signal to an analog signal; and

routing the analog signal through a third capacitor to the sensing node.

8. The method of claim 7, wherein the MEMS includes a capacitance and the digital signal is representative of the capacitance of the MEMS.

9. The method of claim 7, further including:

modulating a reference voltage with a modulating signal to generate the second voltage variation through the second capacitor; and

demodulating the first signal and second signal prior to the integration.

10. The method of claim 7, further including modulating the analog signal with a modulating signal to the third capacitor.

11. The method of claim 7, further including:

providing a charge pump; and

applying a voltage from the charge pump to the sensing node.

12. A semiconductor device for measuring a microelectromechanical system (MEMS), comprising:

a sensing node for measuring the MEMS;

a first integrator;

a first capacitor coupled between the sensing node and an input of the first integrator;

an analog-to-digital converter (ADC) including an input coupled to an output of the first integrator and an output providing a digital signal representative of the state of the MEMS; and

a feedback circuit coupled between the output of the ADC and the sensing node.

13. The semiconductor device of claim 12, wherein the MEMS includes a capacitance and the digital signal is representative of the capacitance of the MEMS.

14. The semiconductor device of claim 12, further including:

a modulator including a first input coupled for receiving a reference voltage and a second input coupled for receiving a modulating signal;

a demodulator including a first input coupled to the first capacitor, second input coupled for receiving a demodulating signal, and output coupled to the input of the integrator; and

a second capacitor coupled between an output of the modulator and the first input of the demodulator.

15. The semiconductor device of claim 12, wherein the feedback circuit includes:

a digital-to-analog converter (DAC) including an input coupled to the output of the ADC; and

a second capacitor coupled between an output of the DAC and the sensing node.

16. The semiconductor device of claim 15, further including a modulator including a first input coupled to the output of the DAC and a second input coupled for receiving a modulating signal with the second capacitor coupled between an output of the modulator and the sensing node.

17. The semiconductor device of claim 12, further including:

a second integrator including an input coupled to the output of the first integrator and an output coupled to the input of the ADC; and

a second capacitor coupled between the sensing node and the input of the second integrator.

18. The semiconductor device of claim 12, further including a charge pump coupled to the sensing node.

19. The semiconductor device of claim 12, further including a semiconductor package containing the semiconductor device with a pin of the semiconductor package coupled to the sensing node.

20. A method of measuring a microelectromechanical system (MEMS), comprising:

sensing a state of the MEMS as a first voltage variation at a sensing node;

transferring the first voltage variation through a first capacitor to a second node as a first signal;

integrating the first signal to provide an integrated signal; and

converting the integrated signal to a digital signal representative of the state of the MEMS.

21. The method of claim 20, wherein the MEMS includes a capacitance and the digital signal is representative of the capacitance of the MEMS.

22. The method of claim 20, further including:

providing a second voltage variation through a second capacitor to the second node as a second signal; and

integrating the first signal and second signal to provide the integrated signal.

23. The method of claim 22, further including:

modulating a reference voltage with a modulating signal to generate the second voltage variation through the second capacitor; and

demodulating the first signal and second signal prior to the integration.

24. The method of claim 20, further including:

converting the digital signal to an analog signal; and

routing the analog signal through a second capacitor to the sensing node.

25. The method of claim 24, further including modulating the analog signal with a modulating signal to the second capacitor.