Impedance detection apparatus and method of physical variable

• US 6,373,264 B1
• Filed: 10/08/1999
• Issued: 04/16/2002
• Est. Priority Date: 02/19/1998
• Status: Expired due to Fees

• Current Assignee: Tokyo Electron Limited
• Original Assignee: Sumitomo Metal Industries Limited (Nippon Steel Corporation)
• Inventors: Miyano, Takaya, Harada, Muneo, Hirota, Yoshihiro, Matsumoto, Toshiyuki
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Deb, Anjan
• Application Number:
  US09/402,724
• Time in Patent Office: 921 Days
• Field of Search: 324/678, 324/667, 324/674, 324/681, 324/691, 324/710, 324/680, 324/658, 324/666, 324/76.69, 324/76.39, 324/76.48, 324/663, 733/350.2, 323/364, 323/369, 323/370, 331/65
• US Class Current: 324/667
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01D 5/2405 by varying dielectric
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G01H 11/06 by electric means
• CPC Class Codes: H04R 5/04 Circuit arrangements, e.g. for selective connection of amplifier inputs/outputs to loudspeakers, for loudspeaker detection, or for adaptation of settings to personal preferences or hearing impairments combinations of amplifiers H03F3/68; stereophonic systems H04S

Abstract

An apparatus for detecting an impedance variable in response to a sensed physical amount of a sensor is provided which comprises an impedance-frequency conversion unit and a counter. The impedance-frequency conversion unit converts the sensor impedance to an oscillation signal a frequency of which corresponds to the sensor impedance. The impedance-frequency conversion unit comprises an impedance-voltage converter for providing a voltage corresponding to the sensor impedance, and a Wien bridge oscillator including an element an impedance of which varies in response to the voltage from the impedance-voltage converter, for generating the oscillation signal. The Wien bridge oscillator is capable of generating a square wave signal as the oscillation signal. The counter counts the number of waves (or wave number) of the oscillation signal in a predetermined time period to output a count value which can be handled as a digital signal.

Claims

1. An apparatus for detecting a sensor impedance which varies in response to a sensed physical amount of at least one sensor, comprising:

an impedance-frequency conversion unit for converting the sensor impedance to a square wave oscillation signal, and comprising a Wien bridge oscillator which includes an amplifier, the sensor impedance and positive and negative feedback circuits of the amplifier;

a product of a gain of the amplifier and a positive feedback ratio of the positive feedback circuit being more than or equal to one.

2. The apparatus according to claim 1, wherein the positive feedback circuit includes a resistor and capacitor as the sensor impedance.

3. The apparatus according to claim 1, wherein the amplifier has a variable gain.

4. The apparatus according to claim 1, further comprising a counter for counting the number of waves of the oscillation signal in a predetermined time period;

and

wherein the sensor impedance has one end connected to a reference voltage.

5. The apparatus according to claim 1, further comprising additional sensors, wherein the impedance-frequency conversion unit further comprises additional oscillators including the additional sensor impedances.

6. The apparatus according to claim 5, further comprising a counter for counting the number of waves of the oscillation signal in a predetermined time period;

and

wherein the sensors are constituted as a resonator array and the oscillators generate square wave signals as oscillation signal.

7. An apparatus for detecting a sensor impedance which varies in response to a sensed physical amount of at least one sensor comprising:

an impedance-frequency conversion unit for converting the sensor impedance to an oscillation signal, comprising;

an impedance-voltage converter for providing an output voltage corresponding to the sensor impedance; and

an oscillator for generating the oscillation signal including a variable impedance element, an impedance of which varies in response to the output voltage of the impedance-voltage converter, an amplifier and positive and negative feedback circuits of the amplifier,

a product of a gain of the amplifier and a positive feedback ratio of the positive feedback circuit being more than or equal to one.

8. The apparatus according to claim 7, wherein a frequency of the oscillator depends on an impedance of the variable impedance element.

9. The apparatus according to claim 7, further comprising a voltage adding unit for adding a predetermined DC voltage to the output voltage of the impedance-voltage converter.

10. The apparatus according to claim 9, wherein the variable impedance element of the oscillator is formed by a drain-source resistance of a first MOS FET which is variable by a voltage applied to a gate thereof, and the voltage adding unit comprises a second MOS FET having a gate connected to receive the output voltage corresponding to the sensor impedance, and a drain connected to a variable load resistor and providing the added voltage to the gate of the first MOS FET.

11. The apparatus according to claim 10, the impedance-voltage converter further comprises:

a first operational amplifier having an inverting input connected to receive an input voltage through a resistor and connected to its output through a resistor, and a non-inverting input connected to receive the input voltage through the sensor impedance and connected to a reference voltage terminal through a first switch, wherein the input voltage is variable when the switch is turned off;

a second operational amplifier having an inverting input connected to receive the input voltage through a resistor and connected to its output through a resistor, and a non-inverting input connected to a reference voltage terminal; and

a third operational amplifier having a non-inverting input connected to receive an output voltage from the first operational amplifier, an inverting input connected to receive an output voltage from the second operational amplifier and connected to its output through a variable resistor, the output being connected to the gate of the second MOS FET.

12. The apparatus according to claim 11, further comprising first through third switches which connect the outputs of the first through third operational amplifier with the inverting inputs thereof, respectively.

13. The apparatus according to claim 12, wherein the first through third switches are turned on during a reset cycle.

14. The apparatus according to claim 13, wherein the first through third switches are turned off before starting a measurement cycle.

15. The apparatus according to claim 7, further comprising a counter for counting the number of waves of the oscillation signal in a predetermined time period;

and

wherein the variable impedance element of the oscillator is a resistive one.

16. The apparatus according to claim 7, wherein the sensor impedance is a capacitor.

17. The apparatus according to claim 7, wherein the sensor impedance is a capacitor, and the impedance-voltage converter comprises:

a first operational amplifier having an inverting input connected to receive an input voltage through a resistor and connected to its output through a resistor, and a non-inverting input connected to receive the input voltage through the sensor impedance and connected to a reference voltage terminal through a first switch, wherein the input voltage is variable when the switch is turned off.

18. A method of detecting a capacitance which varies in response to a sensed physical amount of a sensor, comprising the steps of:

converting the sensor capacitance to a voltage corresponding thereto;

varying a resistance of an element in response to the converted voltage;

generating a frequency signal from an oscillator, which varies in response to the resistance of the element; and

counting the number of waves of the frequency signal from the oscillator in a predetermined time period, whereby the sensor capacitance is converted to the oscillation frequency signal which is a digital form.

19. The method according to claim 18, wherein the converting step comprises the steps of:

providing an input voltage to inverting and non-inverting inputs of a first operational amplifier through a resistor and the sensor, and an inverting input of a second operational amplifier through a resistor, a non-inverting input of the second operational amplifier being connected to a reference voltage terminal; and

providing output voltages of the first and second operational amplifier to inverting and non-inverting inputs of a third operational amplifier to differentially amplifying the output voltages thereof, whereby the voltage proportional to the sensor capacitance is outputted from the third operational amplifier.

20. The method according to claim 19, wherein the first through third operational amplifiers include first through third negative feedback circuits comprising first through third resistors and first through third switches connected in parallel to each other, respectively, and the non-inverting input of the first operational amplifier is connected to the reference voltage terminal through a fourth switch, the method further comprising the steps of:

turning on the first through fourth switches during a reset cycle; and

turning off the first through fourth switches before starting a measurement cycle.

21. An apparatus for detecting a sensor impedance, which varies in response to a sensed physical amount of at least one sensor comprising:

an impedance-frequency converter for providing an output voltage corresponding to the sensor impedance;

an oscillator including a variable impedance element which varies in response to the output voltage of the impedance-frequency converter; and

a voltage adding unit connected between he impedance-frequency converter and the oscillator.