CAPACITANCE-VOLTAGE CONVERTER

• US 3,886,447 A
• Filed: 05/16/1973
• Issued: 05/27/1975
• Est. Priority Date: 05/17/1972
• Status: Expired due to Term

• Current Assignee: Katsuaki Tanaka
• Original Assignee: Katsuaki Tanaka
• Inventors: Tanaka, Katsuaki
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/360,690
• Time in Patent Office: 741 Days
• Field of Search: 324/6CD
• US Class Current: 324/678
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

A capacitance-voltage converter, in which an unknown capacitance of a measured capacitor is converted to an output dc voltage indicative of the unknown capacitance. The measured capacitor is charged by a reference dc voltage. All the charge of the measured capacitor is transferred to a reference capacitor, after discharging the reference capacitor, by connecting the terminals of the measured capacitor to the input and the output of an impedance converter, which has a high-impedance input and a lowimpedance output. The reference capacitor is connected to the high-impedance input of the impedance converter. The output dc voltage is derived from the output of the impedance converter.

Claims

1. A capacitance-voltage converter, comprising:

a reference voltage source for producing a reference dc voltage and having one terminal connected to ground;

a first impedance converter having a high input impedance and a low output impedance and assuming the same voltage at the input and the output thereof;

a second impedance converter;

a shield wire having an inner conductor and an outer conductor shielding the inner conductor, the inner conductor having one end connected to one terminal of a measured capacitor of an unknown capacitance and having the other end connected to the input of the second impedance converter, the outer conductor being connected to the output of the second impedance converter;

a connection line having one end conneCted to the other terminal of the measured capacitor;

a first switch for selectively connecting the other end of the connection line to ground or the output of the first impedance converter;

a second switch gang-controlled with the first switch for selectively connecting the input of the second impedance converter to the other terminal of the reference voltage source or the input of the first impedance converter;

a reference capacitor connected across ground and the input of the first impedance converter;

a third switch connected in parallel with the reference capacitor for opening or closing the terminals of the reference capacitor; and

output terminal means connected to the output of the first impedance converter for obtaining an output voltage corresponding to the unknown capacitance.

2. A capacitance-voltage converter according to claim 1 further comprising:

a fourth switch and a voltage-hold capacitor connected in series with the voltage-hold capacitor grounded and the switch connected to the output of the first impedance converter; and

a differential amplifier having one input connected to the output of the first impedance converter and the other input connected to a junction between the voltage-hold capacitor and the fourth switch.

3. A capacitance-voltage converter, comprising:

a reference voltage source for producing a reference dc voltage;

an impedance converter having a high input impedance and a low output impedance and developing a voltage at the output equal to the voltage at the input thereof;

a first switch connected in series to a capacitor of unknown capacitance to be determined to form a series-connection of the first switch and the measured capacitor;

gang-switches for selectively connecting the terminals of said series-connection to the terminals of the reference voltage source or the input and the output of the impedance converter;

a reference capacitor connected across ground and the input of said impedance converter;

a second switch connected in parallel with the terminals of the reference capacitor for opening or closing the terminals of the reference capacitor;

a second series-connection of a third switch and a voltage-hold capacitor connected across ground and the output of the impedance converter so that the voltage-hold capacitor is connected to the ground;

a differential amplifier having one input connected to the output of the impedance converter and the other input connected to a junction between the voltage-hold capacitor and the third switch; and

output terminal means connected to the output of the differential amplifier for providing an output voltage corresponding to the unknown capacitance.