Sensor interface circuit and sensor module

Patent metadata

Field	Value
Publication number	US-12401366-B2
Application number	US-202118286656-A
Country	US
Kind code	B2
Filing date	May 26, 2021
Priority date	May 26, 2021
Publication date	Aug 26, 2025
Grant date	Aug 26, 2025

Abstract

A sensor interface circuit includes a frequency synchronization circuit connectable to a sensor. The frequency synchronization circuit includes: a reference voltage source generating a reference voltage; a current source connected to the reference voltage source, and generating a current by using the reference voltage; a voltage difference detection circuit including first and second input nodes and an output node, generating a control voltage according to a difference between voltages received at the first and second input nodes, one of the voltages received at the first and second input nodes corresponding to a detection value of the sensor; a voltage-controlled oscillation circuit connected to the output node, and generating an oscillation signal according to the control voltage; and a frequency/impedance conversion circuit connected between the voltage-controlled oscillation circuit and the second input node, and converting a frequency of a signal according to the oscillation signal into impedance.

First claim

What is claimed is:

1. A sensor interface circuit comprising:
a frequency synchronization circuit connectable to a sensor,
the frequency synchronization circuit including:
a reference voltage source configured to generate a reference voltage;
a current source connected to the reference voltage source, the current source being configured to generate a current by using the reference voltage;
a voltage difference detection circuit including a first input node connected to the reference voltage source, a second input node connected to the current source, and an output node, one of a voltage received at the first input node and a voltage received at the second input node corresponding to a detection value of the sensor, and the voltage difference detection circuit being configured to generate a control voltage according to a difference between the voltage received at the first input node and the voltage received at the second input node;
a voltage-controlled oscillation circuit connected to the output node of the voltage difference detection circuit, the voltage-controlled oscillation circuit being configured to generate an oscillation signal according to the control voltage; and
a frequency/impedance conversion circuit connected between the voltage-controlled oscillation circuit and the second input node of the voltage difference detection circuit, the frequency/impedance conversion circuit being configured to convert a frequency of a signal according to the oscillation signal into impedance.

2. The sensor interface circuit according to claim 1 , wherein
the current source is connectable to the sensor and is configured to generate a current by using the reference voltage and the detection value of the sensor, and
in the voltage difference detection circuit, the voltage received at the second input node corresponds to the detection value of the sensor and the frequency.

3. The sensor interface circuit according to claim 2 , wherein
the current source includes:
a first transistor connected between a second potential and the second input node of the voltage difference detection circuit;
a second transistor connectable between the second potential and the sensor; and
a differential amplification circuit including a first input node connected to the reference voltage source, a second input node connected to a node between the second transistor and the sensor, and an output node connected in common to a gate of the first transistor and a gate of the second transistor.

4. The sensor interface circuit according to claim 1 , further comprising:
an amplification circuit connected between the reference voltage source and the voltage difference detection circuit and connectable to the sensor, the amplification circuit being configured to amplify a difference between the reference voltage and the detection value of the sensor and output a voltage according to the amplified difference, wherein
in the voltage difference detection circuit, the voltage received at the first input node corresponds to the detection value of the sensor, and the voltage received at the second input node corresponds to the frequency.

5. The sensor interface circuit according to claim 4 , wherein
the current source includes:
a resistive element;
a first transistor connected between a second potential and the second input node of the voltage difference detection circuit;
a second transistor connected between the second potential and the resistive element; and
a differential amplification circuit including a first input node connected to the amplification circuit, a second input node connected to a node between the second transistor and the resistive element, and an output node connected in common to a gate of the first transistor and a gate of the second transistor.

6. The sensor interface circuit according to claim 1 , further comprising:
a frequency division circuit connected between the voltage-controlled oscillation circuit and the frequency/impedance conversion circuit, the frequency division circuit being configured to perform frequency division on the oscillation signal, wherein
the frequency/impedance conversion circuit is configured to convert a frequency of the signal subjected to frequency division into impedance.

7. The sensor interface circuit according to claim 1 , wherein the frequency/impedance conversion circuit is configured with a switched capacitor circuit.

8. The sensor interface circuit according to claim 7 , wherein
the frequency/impedance conversion circuit includes:
a first capacitive element of which one end is connected to a first potential;
a second capacitive element of which one end is connected to the first potential and another end is connected to the second input node of the voltage difference detection circuit;
a first switch of which one end is connected to the second input node of the voltage difference detection circuit, another end is connected to another end of the first capacitive element, and a control end is connected to the voltage-controlled oscillation circuit;
an inverter connected to the voltage-controlled oscillation circuit; and
a second switch of which one end is connected to the other end of the first capacitive element, another end is connected to the first potential, and a control end is connected to the inverter.

9. A sensor module comprising:
an antenna;
an impedance conversion circuit;
a sensor; and
the sensor interface circuit according to claim 1 , the sensor interface circuit being connected between the sensor and the antenna.

Assignees

• Nisshinbo Micro Devices Inc
• Tokyo Inst Tech
• Alps Alpine Co Ltd

Inventors

• Sato Hiroki
• Sato Masayuki
• Shirakawa Takaaki
• Pan Chunhui
• Ishihara Noboru
• Murata Shinji

Classifications

• H03K17/6871

  the output circuit comprising more than one controlled field-effect transistor · CPC title

• G01R27/02

  Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant (by measuring phase angle only G01R25/00) · CPC title

• H03L7/093 Primary

  using special filtering or amplification characteristics in the loop (H03L7/087 - H03L7/091 take precedence) · CPC title