# US 8,786,296 B2 · Resistance-measuring circuit and electronic device using the same

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- Number: US 8,786,296 B2
- Document ID: US8786296B2
- Status: Granted
- Kind: B2
- Application number: 13/278,075
- Filed: 2011-10-20
- Published: 2012-08-30
- Granted: 2014-07-22
- Earliest claimed: 2011-02-28
- Assignees: Fu Tai Hua Industry (Shenzhen) Co., Ltd.; Hon Hai Precision Industry Co., Ltd.
- Applicants: Qi-Long Yu; Tsung-Jen Chuang; Jun Zhang; Jun-Wei Zhang; Shih-Fang Wong; Jian-Jun Zhou
- Inventors: Qi-Long Yu; Tsung-Jen Chuang; Jun Zhang; Jun-Wei Zhang; Shih-Fang Wong; Jian-Jun Zhou
- Web page: https://patentgrep.com/patent/US8786296B2

## CPC

- G01R 27/14: Measuring resistance by measuring current or voltage obtained from a reference source (G01R27/16, G01R27/20, G01R27/22 take precedence)
- G01D 5/246: by varying the duration of individual pulses
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR

## Abstract

A resistance-measuring circuit includes a controller for outputting a PWM signal and further for adjusting the duty cycle of the PWM signal, and a sampling circuit for processing the PWM signal and transmitting the processed PWM signal to the sensor. The sampling circuit samples the signal outputted from the sensor to generate a sampled signal with the voltage thereof changing according to any change in the duty cycle of the PWM signal, and further transmits the sampled signal to the controller. The controller obtains the real-time duty cycle of the PWM signal when the voltage of the sampled signal reaches a threshold voltage, and further calculates the exact resistance of the sensor according to the obtained real-time duty cycle of the PWM signal and the threshold voltage. An electronic device with the resistance-measuring circuit is also provided.

## Claims

### Claim 1

A resistance-measuring circuit for measuring resistance of a sensor, comprising:
a controller for outputting a PWM signal and further adjusting the duty cycle of the PWM signal; and
a sampling circuit electrically connecting the controller to the sensor, and used for processing the PWM signal and transmitting the processed PWM signal to the sensor;
wherein the sampling circuit samples the signal outputted from the sensor to generate a sampled signal with the voltage thereof changing according to the change of the duty cycle of the PWM signal, and further transmits the sampled signal to the controller; the controller obtains the real-time duty cycle of the PWM signal when the voltage of the sampled signal reaches a threshold voltage, and further calculates the resistance of the sensor according to the obtained real-time duty cycle of the PWM signal and the threshold voltage; wherein the sampling circuit comprises a voltage-converting unit and a sampling unit, the voltage-converting unit is used to convert the PWM signal to a direct-voltage signal which changes according to the change of the duty cycle of the PWM signal and further transmit the direct-voltage signal to the sensor to be processed, the sampling unit is used to sample the direct-voltage signal processed by the sensor to generate the sampled signal; wherein the controller comprises an output port for outputting the PWM signal, and an input port for receiving the sampled signal generated by the sampling circuit; and wherein the sampling unit comprises a first resistor, the voltage-converting unit comprises a capacitor and a second resistor, a terminal of the sensor is electrically connected to the output port of the controller via the second resistor, the other terminal of the sensor is grounded via the first resistor; a terminal of the capacitor is electrically connected between the sensor and the second resistor, and the other terminal of the capacitor is grounded; the input port of the controller is electrically connected between the sensor and the second resistor.

### Claim 2 (depends on 1)

The resistance-measuring circuit of claim 1, wherein the sampling circuit further comprises an amplifier for electrically connecting the voltage-converting unit to the sensor, the amplifier is used to process the direct-voltage signal to stabilize the output of the voltage-signal.

### Claim 3 (depends on 2)

The resistance-measuring circuit of claim 2, wherein the amplifier comprises an operational amplifier, the non-inverting input of the operational amplifier is electrically connected to the output port of the controller and is further grounded via the capacitor; the inverting input of the operational amplifier is electrically connected to the output of the operational amplifier.

### Claim 4 (depends on 3)

The resistance-measuring circuit of claim 3, wherein the resistance of the sensor is obtained according to the formula: R3=(Duty/K−1)*R1; R1 is the resistance of the first resistor, Duty is the real-time duty of the PWM signal when the voltage of the sampled signal reaches the threshold voltage, and K is a constant and indicates the relationship between the threshold voltage and the rising-edge voltage of the PWM signal.

### Claim 5 (depends on 4)

The resistance-measuring circuit of claim 4, wherein the rising-edge voltage of the PWM signal is the work voltage of the controller, and the failing-edge voltage of the PWM signal is 0.

### Claim 6 (depends on 1)

The resistance-measuring circuit of claim 1, wherein the controller comprises a Pulse Width Modulation (PWM) module for generating a PWM signal, an adjusting module for adjusting the duty cycle of the PWM signal to adjust the voltage of the sampled signal, and a calculating module for obtaining the real-time duty cycle of the PWM signal when the voltage of the sampled signal reaches a threshold voltage, and further calculating the resistance of the sensor according to the real-time duty cycle and the threshold voltage.

### Claim 7

An electronic device comprising:
a sensor; and
a resistance-measuring circuit for measuring the resistance of the sensor, the resistance-measuring circuit comprising:
a controller for outputting a PWM signal and further adjusting the duty cycle of the PWM signal; and
a sampling circuit electrically connecting the controller to the sensor, and used for processing the PWM signal and transmitting the processed PWM signal to the sensor;
wherein the sampling circuit samples the signal outputted from the sensor to generate a sampled signal with the voltage thereof changing according to the change of the duty cycle of the PWM signal, and further transmits the sampled signal to the controller; the controller obtains the real-time duty cycle of the PWM signal when the voltage of the sampled signal reaches a threshold voltage, and further calculates the resistance of the sensor according to the obtained real-time duty cycle of the PWM signal and the threshold voltage; wherein the sampling circuit comprises a voltage-converting unit and a sampling unit, the voltage-converting unit is used to convert the PWM signal to a direct-voltage signal which changes according to the change of the duty cycle of the PWM signal and further transmit the direct-voltage signal to the sensor to be processed, the sampling unit is used to sample the direct-voltage signal processed by the sensor to generate the sampled signal; wherein the controller comprises an output port for outputting the PWM signal, and an input port for receiving the sampled signal generated by the sampling circuit; and wherein the sampling unit comprises a first resistor, the voltage-converting unit comprises a capacitor and a second resistor, a terminal of the sensor is electrically connected to the output port of the controller via the second resistor, the other terminal of the sensor is grounded via the first resistor; a terminal of the capacitor is electrically connected between the sensor and the second resistor, and the other terminal of the capacitor is grounded; the input port of the controller is electrically connected between the sensor and the second resistor.

### Claim 8 (depends on 7)

The electronic device of claim 7, wherein the sampling circuit further comprises an amplifier for electrically connecting the voltage-converting unit to the sensor, the amplifier is used to process the direct-voltage signal to stabilize the out put of the voltage-signal.

### Claim 9 (depends on 8)

The electronic device of claim 8, wherein the amplifier comprises an operational amplifier, the non-inverting input of the operational amplifier is electrically connected to the output port of the controller and is further grounded via the capacitor; the inverting input of the operational amplifier is electrically connected to the output of the operational amplifier.

### Claim 10 (depends on 9)

The electronic device of claim 9, wherein the resistance of the sensor is obtained according to the formula: R3=(Duty/K−1)*R1; R1 is the resistance of the first resistor, Duty is the real-time duty of the PWM signal when the voltage of the sampled signal reaches the threshold voltage, the K is constant and indicates the relationship between the threshold voltage and the rising-edge voltage of the PWM signal.

### Claim 11 (depends on 10)

The electronic device of claim 10, wherein the rising-edge voltage of the PWM signal is the work voltage of the controller, and the failing-edge voltage of the PWM signal is 0.

### Claim 12 (depends on 7)

The electronic device of claim 7, wherein the controller comprises a Pulse Width Modulation (PWM) module for generating a PWM signal, an adjusting module for adjusting the duty cycle of the PWM signal to adjust the voltage of the sampled signal, and a calculating module for obtaining the real-time duty cycle of the PWM signal when the voltage of the sampled signal reaches a threshold voltage, and further calculating the resistance of the sensor according to the real-time duty cycle and the threshold voltage.