Continuous-time sensing apparatus

Patent metadata

Field	Value
Publication number	US-10574259-B2
Application number	US-201715723814-A
Country	US
Kind code	B2
Filing date	Oct 3, 2017
Priority date	Oct 3, 2017
Publication date	Feb 25, 2020
Grant date	Feb 25, 2020

Abstract

A system includes a sensor device, a circuit driving he sensor device at a drive frequency, a receiver, and a low pass filter. The sensor device is configured to change its electrical characteristics in response to external stimuli. The sensor device generates a modulated signal proportional to the external stimuli. The receiver is configured to receive the modulated signal and further configured to demodulate the modulated signal to generate a demodulated signal. The demodulation signal has a guard band. The receiver consumes power responsive to receiving the modulated signal. The low pass filter is configured to receive the demodulated signal and further configured to generate a sensor output.

First claim

What is claimed is:

1. An apparatus comprising:
a sensor device configured to change its electrical characteristics in response to external stimuli;
a circuit driving the sensor device at a drive frequency, wherein the sensor device uses a modulation signal to generate a modulated signal proportional to the external stimuli;
a receiver configured to receive the modulated signal and further configured to demodulate the modulated signal to generate a demodulated signal, wherein a demodulation signal is a rectangular wave that has a guard band and is used to demodulate the modulated signal, and wherein the modulation signal is different from the demodulation signal; and
a low pass filter configured to receive the demodulated signal and further configured to generate a sensor output.

2. The apparatus as described in claim 1 further comprising:
an analog to digital converter configured to receive the demodulated signal without passing through a sample and hold circuitry, and wherein the analog to digital converter is further configured to generate a digital signal output.

3. The apparatus as described in claim 2 , wherein the drive frequency is decoupled from a frequency associated with the analog to digital converter.

4. The apparatus of claim 2 , wherein a frequency associated with the demodulation signal is decoupled from a sampling frequency associated with the analog to digital converter.

5. The apparatus as described in claim 1 , wherein the modulation signal used to generate the modulated signal has a waveform that is different from a waveform of the demodulation signal used by the receiver.

6. The apparatus as described in claim 1 , wherein the receiver comprises a differential circuit including commutation and blocking switches.

7. The apparatus as described in claim 6 , wherein the switches are controlled by a demodulation signal waveform used to demodulate the modulated signal.

8. The apparatus as described in claim 1 , wherein the sensor device is a micro-electromechanical system (MEMS) device.

9. The apparatus as described in claim 1 , wherein charges on a capacitance of the sensor device changes in response to the external stimuli.

10. The apparatus as described in claim 1 , wherein a resistance of the sensor device varies in response to the external stimuli.

11. The apparatus as described in claim 9 , wherein the receiver comprises an amplifier coupled to an output of the sensor device, and wherein a capacitor is in parallel to a resistor that are coupled to an input of the amplifier from an output of the amplifier, wherein the resistor biases the input of the amplifier, and wherein the output of the amplifier is the modulated signal voltage.

12. The apparatus as described in claim 11 , wherein the resistor is a switched-cap resistor.

13. The apparatus of claim 1 , wherein a frequency of the modulation signal is different from a frequency of the demodulation signal.

14. An apparatus comprising:
a sensing capacitor of a sensing device configured to generate electrical charges in response to external stimuli, wherein the sensing device is driven at a drive frequency, and wherein the sensing device uses a modulation signal to generate a modulated signal proportional to the external stimuli;
an amplifier coupled to the sensing capacitor, wherein the amplifier receives the modulated signal and wherein the amplifier is configured to convert the modulated signal into a voltage signal;
a demodulator configured to demodulate the voltage signal to generate a demodulated signal, wherein a demodulation signal is a rectangular wave that has a guard band and is used to demodulate the modulated signal, and wherein the modulation signal is different from the demodulation signal, and wherein the amplifier consumes power responsive to receiving the modulated signal; and
a low pass filter configured to receive the demodulated signal and further configured to generate a sensor output.

15. The apparatus as described in claim 14 further comprising:
an analog to digital converter configured to receive the demodulated signal and wherein the analog to digital converter is further configured to generate a digital signal output, and wherein the analog to digital converter comprises embedded anti-aliasing filter.

16. The apparatus as described in claim 15 , wherein the drive frequency is decoupled from a frequency associated with the analog to digital converter.

17. The apparatus as described in claim 14 , wherein the modulation signal used to generate the modulated signal has a waveform that is different from a waveform of a demodulation signal used by the demodulator.

18. The apparatus as described in claim 14 , wherein the sensing device is a micro-electromechanical system (MEMS) device.

19. The apparatus as described in claim 14 , wherein a capacitor is in parallel to a resistor that are coupled to an input of the amplifier from an output of the amplifier, wherein the resistor biases the input of the amplifier, and wherein the output of the amplifier is the modulated signal voltage.

20. The apparatus as described in claim 19 , wherein the resistor is a switched-cap resistor.

21. A method comprising:
changing a capacitance associated with a sensor responsive to an external stimulus;
driving the capacitance associated with the sensor;
generating a modulated electrical signal responsive to the driving;
demodulating the modulated electrical signal to generate a demodulated signal, wherein a modulation signal used to generate the modulated electrical signal is different from a demodulation signal used to generate the demodulated signal, and wherein the demodulation signal is a rectangular wave that has a guard band; and
converting the demodulated signal to a digital signal, wherein a frequency associated with converting the demodulated signal to the digital signal is decoupled from a drive frequency of the sensor device.

22. The method as described in claim 21 , wherein no sampling is performed prior to the converting.

23. The method as described in claim 21 , wherein a carrier signal associated with the demodulating is a guard-band signal.

24. The method as described in claim 21 , wherein the capacitance is driven with a voltage or current.

Assignees

• Invensense Inc

Inventors

• Chen Du
• Tsinker Vadim
• Wang Stanley Bo-Ting

Classifications

• H03M11/02

  Details · CPC title

• G06F3/044

  by capacitive means · CPC title

• H03M5/02 Primary

  Conversion to or from representation by pulses · CPC title

• H03K17/9625

  using a force resistance transducer · CPC title

• H03K17/9622

  using a plurality of detectors, e.g. keyboard · CPC title