PARASITIC CAPACITANCE CANCELLATION IN CAPACITIVE MEASUREMENT

• US 20140285220A1
• Filed: 02/24/2014
• Published: 09/25/2014
• Est. Priority Date: 10/15/2008
• Status: Active Grant

• Current Assignee: Azoteq Holdings Limited
• Original Assignee: Azoteq Pty Ltd.
• Inventors: Bruwer, Frederick Johannes, Mellet, Dieter Sydney-Charles, Van Der Merwe, Douw Gerbrandt, Swanepoel, Johann
• Granted Patent: US 9,360,510 B2
• Time in Patent Office: Days
• US Class Current: 324/659
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G01R 27/2611 Measuring inductance
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

An integrated circuit compensates for parasitic capacitance in a capacitive measuring apparatus wherein a capacitance measurement is done by repeatedly transferring charge from a capacitor to be measured to a reference capacitor.

Claims

1. An integrated circuit for measuring capacitance of a capacitive structure using a charge transfer technique, said circuit comprising means for transferring charge during each of a plurality of cycles during a capacitive measurement to a reference capacitor wherein the charge transferred from the measured capacitive structure and accumulated in the reference capacitor during every cycle in the capacitive measurement is reduced by a predetermined amount of charge.

2. The integrated circuit of claim 1 wherein the charge transferred for measurement is scaled using a current mirror structure.

3. The integrated circuit of claim 1 further comprising a current mirror structure for scaling the amount of charge that is removed every cycle.

4. The integrated circuit of claim 1 wherein the reference capacitor is located on a chip for the integrated circuit.

5. The integrated circuit of claim 1 further including a number of selectable on-chip capacitors, and wherein the selection of said on-chip capacitors determines the amount of charge removed during every cycle.