Apparatus for and method of measuring capacitance with high accuracy

• US 6,683,462 B2
• Filed: 11/02/2001
• Issued: 01/27/2004
• Est. Priority Date: 11/30/2000
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Shimizu, Akira
• Primary Examiner(s): Snow, Walter E.
• Assistant Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US10/004,333
• Publication Number:
  US 20020101251A1
• Time in Patent Office: 816 Days
• Field of Search: 324/519, 324/548, 324/658, 324/660, 324/661, 324/679, 324/686, 324/662, 324/663, 324/677, 324/713, 324/765, 324/158.1
• US Class Current: 324/658
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G01R 31/2639 for testing field-effect devices, e.g. of MOS-capacitors G01R31/2621 takes precedence

Abstract

For measuring a capacitance with high accuracy, a capacitance measuring apparatus includes a voltage source with a current limiting function for applying different voltage values to the capacitance, and an integrator capable of continuous integrating operation for repeatedly integrating a current flowing through the capacitance at given periodic intervals. There is also disclosed a capacitance measuring method that is carried out by the capacitance measuring apparatus.

Claims

1. An apparatus for measuring a capacitance, comprising:

a voltage source having a current limiting function and capable of applying different voltages to the capacitance, the voltage source comprising a variable-output voltage source, a variable-output current source, and a current detector that is selectively connectable to said variable-output voltage source or said variable-output current source depending on a current flowing therethrough; and

an integrator capable of continuous integration operation for repeatedly integrating a current flowing through the capacitance at constant periodic intervals the integrator comprising two constant current sources whose polarities are opposite to each other and are each connected through a switch to an input of an operational amplifier shunted by a capacitor having a known capacitance, and a comparator/counter connected to an output of the amplifier for turning the switch on and off.

2. An apparatus according to claim 1, further comprising a current-to-voltage converter connected between said capacitance and said integrator for causing said integrator to integrate an output voltage from said current-to-voltage converter.

3. An apparatus according to claim 1, wherein the voltage source applies a step voltage.

4. A method of measuring a capacitance, comprising the steps of:

imparting a voltage change from a voltage value to another voltage value to the capacitance while limiting a current flowing through the capacitance so that the current does not exceed a predetermined value using a voltage source which has a current limiting function comprising a variable-output voltage source, a variable-output current source, and a current detector which is selectively connectable to said variable-output voltage source or said variable-output current source depending on a current flowing therethrough;

repeatedly integrating a current flowing through the capacitance at constant periodic intervals during the voltage change and outputting integrated values using an integrator comprising two constant current sources whose polarities are opposite to each other which are each connected through a switch to an input of an operational amplifier shunted by a capacitor having a known capacitance, and a comparator/counter connected to an output of the amplifier for turning the switch on and off;

summing the outputted integrated values using the comparator/counter to determine a current value flowing through the capacitance in relation to said voltage change of the amplifier; and

calculating a value of the capacitance based on the calculated current value.

5. A method according to claim 4, further comprising the steps of:

converting the current flowing through the capacitance into a voltage; and

repeatedly integrating the voltage converted from said current.