FORCE FEEDBACK LOOP FOR PRESSURE SENSORS

• US 20150285701A1
• Filed: 04/07/2014
• Published: 10/08/2015
• Est. Priority Date: 04/07/2014
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Hammerschmidt, Dirk
• Granted Patent: US 9,645,029 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B81B 3/0059 Constitution or structural means for controlling the movement not provided for in groups B81B3/0037 - B81B3/0056
• CPC Class Codes: G01L 1/086 using electrostatic or electromagnetic counterbalancing forces
• CPC Class Codes: G01L 1/144 with associated circuitry G01L1/146 and G01L1/148 take precedence
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A pressure sensor system comprises a force feedback loop. The force feedback loop is configured to receive a measured pressure sensor signal and generate a feedback signal based on the measured pressure and an electrostatic force. The electrostatic force is generated based on the feedback signal and combined with the measured force keeping the resultant sensor signal stable.

Claims

1. A pressure sensor system, comprising:

a pressure sensor configured to measure a force caused by a pressure and to generate a sensor signal based on the measured pressure force and an electrostatic force; and

a force feedback loop configured to receive the sensor signal and to generate an output signal and a feedback signal based on the sensor signal;

wherein the feedback signal is utilized to generate the electrostatic force on the pressure sensor, wherein the electrostatic force is exerted on the pressure sensor in addition to the pressure force.

2. The system of claim 1, wherein the pressure sensor is a capacitive sensor comprising a diaphragm as a force collector, wherein an overall force exerted on the diaphragm by the electrostatic force and the measured pressure generates an overall capacitance.

3. The system of claim 2, wherein the force feedback loop is configured to adjust the feedback signal in response to the sensor signal so that the overall capacitance caused by the overall force is stable for different pressure measurements.

4. The system of claim 3, wherein the overall capacitance caused by the overall force is equal to or greater than a capacitance caused by a maximum measured pressure on the pressure.

5. The system of claim 1, wherein the pressure sensor is integrated in a micro-electro-mechanical system (MEMS).

6. The system of claim 1, wherein the output signal comprises a digital or analog signal.

7. A signal processing system, comprising:

an input stage configured to measure a source force and to generate a capacitive signal in response to the measured source force and an electrostatic force;

a force feedback loop configured to receive the capacitive signal and to generate an output signal and a feedback driving voltage based on the capacitive signal; and

a force function component configured to generate the electrostatic force based on the feedback driving voltage;

wherein the electrostatic force is combined with the measured source force to generate an overall force.

8. The system of claim 7, wherein an overall capacitance generated by the overall force is stable for different source force measurements.

9. The system of claim 7, wherein the force feedback loop further comprises:

a controller configured to compare a measurement charge and a target charge, and generate a control signal in response to a charge difference;

a digital to analog converter (DAC) configured to convert the digital control signal to a feedback voltage; and

an amplifier configured to amplify the feedback voltage to form the feedback driving voltage.

10. The system of claim 9, wherein the output signal is based on the control signal.

11. The system of claim 9, wherein the feedback driving voltage is applied to the input stage and the controller as a bias voltage.

12. The system of claim 9, wherein the feedback driving voltage is applied to the input stage as a bias voltage, and the feedback voltage is applied to the controller as another bias voltage.

13. The system of claim 9, wherein the amplifier is a charge pump configured to amplify the feedback voltage greater than a supply voltage of the system.

14. The system of claim 9, wherein the digital controller is a proportional-integral-derivate (PID) controller or a state space controller.

15. The system of claim 9, further comprising an analog integrator between the input stage and the digital controller.

16. The system of claim 15, wherein the analog integrator comprises a first integrator stage configured to run at a relatively lower clock frequency and a sigma delta modulator configured to run at a relatively higher frequency.

17. The system of claim 10, further comprising a switched capacitor circuit that generates a comparison result of the measurement charge and the target charge wherein a programmable array of capacitors is connected in parallel to a capacitor of a sensor bridge.

18. A method of operating a pressure sensor system comprises:

measuring a force caused by a pressure using a pressure sensor to generate a sensor signal based on the measured pressure and an electrostatic force;

generating an output signal and a feedback signal via a force feedback loop based on the sensor signal;

generating the electrostatic force based on the feedback signal; and

applying the electrostatic force to the pressure sensor in addition to a force caused by the measured pressure to generate the sensor signal.

19. The method of claim 18, wherein a sensor capacitance and a programmable target capacitance are compared or substracted.

20. The method of claim 18, wherein the feedback signal is generated so that an overall force of the electrostatic force and the measured pressure generates a stable capacitance that is equal to or greater than a capacitance caused by a maximum measured pressure.