Sensor module

Patent metadata

Field	Value
Publication number	US-10830608-B2
Application number	US-201715608088-A
Country	US
Kind code	B2
Filing date	May 30, 2017
Priority date	Dec 5, 2014
Publication date	Nov 10, 2020
Grant date	Nov 10, 2020

Abstract

A detection circuit includes a charge amplifier, a calculation unit, and first and second paths. The charge amplifier converts the amount of electric charge generated by a sensor element into a voltage. The first path and the second path each connect the charge amplifier and the calculation unit. The amplification factor of the first path is higher than the amplification factor of the second path. When a voltage output from the first path is lower than a threshold voltage, the calculation unit detects a pressing force by using the output voltage. When the output voltage is equal to or higher than the threshold voltage, the calculation unit detects a pressing force by using a voltage output through the second path.

First claim

The invention claimed is:

1. A sensor module comprising:
a piezoelectric element configured to generate electric charge in response to a pressing force;
a charge amplifier coupled to the piezoelectric element and configured to convert the electric charge into a voltage;
a calculation unit configured to detect the pressing force based on the voltage output from the charge amplifier;
wherein the calculation unit is connected to an output of the charge amplifier to receive the converted voltage by a first path and a second path having different amplification factors from each other and being connected in parallel between the charge amplifier and the calculation unit,
wherein the calculation unit detects the pressing force based on a first voltage received from the first path when the first voltage is lower than a threshold voltage, and
wherein the calculation unit detects the pressing force based on a second voltage received from the second path when the first voltage is equal to or higher than the threshold voltage.

2. The sensor module according to claim 1 , wherein the amplification factor of the first path is higher than the amplification factor of the second path.

3. The sensor module according to claim 2 , wherein the calculation unit is further configured to correct the voltage of either the first or second voltage used to detect the pressing force based on a ratio of the amplification factor of the first path and the amplification factor of the second path.

4. The sensor module according to claim 1 , wherein the first path includes a first amplification circuit and a first capacitor connected to an input stage of the first amplification circuit.

5. The sensor module according to claim 4 , wherein the second path includes a second amplification circuit having an amplification factor lower than the amplification factor of the first amplification circuit and a second capacitor connected to an input stage of the second amplification circuit.

6. The sensor module according to claim 5 , wherein the capacitance of the first capacitor and the capacitance of the second capacitor are equal to each other.

7. The sensor module according to claim 5 , further comprising:
a first resistor connected in series with the first capacitor and determining the amplification factor of the first amplification circuit; and
a second resistor connected in series with the second capacitor and determining the amplification factor of the second amplification circuit.

8. The sensor module according to claim 5 , further comprising:
a first resistor connected in series with the first capacitor; and
a second resistor connected between an inverting input and an output of the first amplification circuit,
wherein the amplification factor of the first amplification circuit is based on a ratio of a resistance of the second resistor to a resistance of the first resistor.

9. The sensor module according to claim 8 , further comprising:
a third resistor connected in series with the second capacitor; and
a fourth resistor connected between an inverting input and an output of the second amplification circuit,
wherein the amplification factor of the second amplification circuit is based on a ratio of a resistance of the fourth resistor to a resistance of the third resistor.

10. The sensor module according to claim 7 , wherein an impedance of the first resistor and an impedance of the second resistor are equal to each other.

11. The sensor module according to claim 1 , wherein the calculation unit is further configured to:
detect a third voltage received from the first path and a fourth voltage received from the second path when no pressing force is applied on the piezoelectric element,
correct the first voltage using the third voltage when detecting the pressing force based on the first voltage, and
correct the second voltage using the fourth voltage when detecting the pressing force based on the second voltage.

12. The sensor module according to claim 1 , wherein the calculation unit further comprises:
a comparator connected to the first path and configured to compare the first voltage with the threshold voltage; and
a microcomputer configured detect the pressing force based on either the first voltage or the second voltage depending on the output of the comparator.

13. The sensor module according to claim 12 , wherein the threshold voltage is a voltage with a predetermined voltage margin that is lower than a voltage at which an amplification circuit in the first path becomes saturated.

14. The sensor module according to claim 1 , wherein the charge amplifier comprises an operational amplifier having an inverting input coupled to an output of the piezoelectric element and a non-inverting input coupled to a constant potential.

15. The sensor module according to claim 14 , wherein the charge amplifier further comprises a resistor coupled between the inverting input and an output of the operation amplifier and a capacitor coupled in parallel to the resistor.

16. A sensor comprising:
a piezoelectric element that generates electric charge in response to a pressing force;
a charge amplifier that converts the electric charge into a voltage that is proportional to the pressing force;
a first amplification circuit in a first path coupled to an output of the charge amplifier;
a second amplification circuit in a second path coupled to the output of the charge amplifier, wherein the second amplification circuit has a different amplification factor than the first amplification circuit and is connected in parallel with the first amplification circuit between the charge amplifier and the calculation unit;
a determination unit configured to compare a first voltage output from the first amplification circuit to a threshold voltage; and
a calculation unit coupled to each of the output of the first amplification circuit, an output of the second amplification circuit, and an output of the determination unit, the calculation unit being configured to:
detect the pressing force based on the first voltage output from the first amplification unit when the determination unit determines that first voltage is lower than a threshold voltage, and
detect the pressing force based on a second voltage output from the second amplification unit when the determination unit determines that the first voltage is equal to or higher than the threshold voltage.

17. The sensor according to claim 16 , wherein the calculation unit is further configured to correct a voltage used to detect the pressing force based on a ratio of the amplification factor of the first amplification circuit and the amplification factor of the second amplification circuit.

18. The sensor according to claim 16 , further comprising:
a first capacitor connected to an input stage of the first amplification circuit; and
a second capacitor connected to an input stage of the second amplification circuit,
wherein the capacitance of the first capacitor and the capacitance of the second capacitor are equal to each other.

19. The sensor according to claim 16 , wherein the calculation unit is further configured to:
detect, when no pressing force is applied on the piezoelectric element, a third voltage from a first path of the first amplification circuit and a fourth voltage from a second path of the second amplification circuit,
correct the first voltage using the third voltage when detecting the pressing force based on the first voltage, and
correct the second voltage using the fourth voltage when detecting the p

Assignees

• Murata Manufacturing Co

Inventors

• Yamaguchi Yoshihiro

Classifications

• G01D3/02

  with provision for altering or correcting the law of variation · CPC title

• G01R31/44

  Testing lamps · CPC title

• G01R31/28

  Testing of electronic circuits, e.g. by signal tracer ({EMC, EMP or similar testing of electronic circuits G01R31/002;} testing for short-circuits, discontinuities, leakage or incorrect line connection G01R31/50; checking computers {or computer components} G06F11/00; checking static stores for correct operation G11C29/00 {; testing receivers or transmitters of transmission systems H04B17/00}) · CPC title

• G01R1/30

  Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier · CPC title

• G01D3/024 Primary

  for range change; Arrangements for substituting one sensing member by another · CPC title