METHODS AND SYSTEMS FOR GUARDING A CHARGE TRANSFER CAPACITANCE SENSOR FOR PROXIMITY DETECTION

• US 20070268026A1
• Filed: 08/03/2007
• Published: 11/22/2007
• Est. Priority Date: 06/03/2005
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: REYNOLDS, Joseph
• Granted Patent: US 7,417,441 B2
• Time in Patent Office: Days
• US Class Current: 324/686
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 17/965 Switches controlled by moving an element forming part of the switch
• CPC Class Codes: H03K 2017/9602 characterised by the type or shape of the sensing electrodes
• CPC Class Codes: H03K 2217/96058 Fail-safe touch switches, where switching takes place only after repeated touch
• CPC Class Codes: H03K 2217/960725 Charge-transfer
• CPC Class Codes: H03K 2217/960775 Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

Abstract

Methods, systems and devices are described for determining a measurable capacitance for proximity detection in a sensor having a plurality of sensing electrodes and at least one guarding electrode. A charge transfer process is executed for at least two executions. The charge transfer process includes applying a pre-determined voltage to at least one of the plurality of sensing electrodes using a first switch, applying a first guard voltage to the at least one guarding electrode using a second switch, sharing charge between the at least one of the plurality of sensing electrodes and a filter capacitance, and applying a second guard voltage different from the first guard voltage to the at least one guarding electrode. A voltage is measured on the filter capacitance for a number of measurements equal to at least one to produce at least one result to determine the measurable capacitance for proximity detection.

Claims

1. A method for determining a measurable capacitance for proximity detection in a sensor having a plurality of sensing electrodes and at least one guarding electrode proximate the plurality of sensing electrodes, the method comprising:

executing a charge transfer process for a number of executions equal to at least two, wherein the charge transfer process comprises the steps of;

applying a pre-determined voltage to at least one of the plurality of sensing electrodes using a first switch;

applying a first guard voltage to the at least one guarding electrode using a second switch;

sharing charge between the at least one of the plurality of sensing electrodes and a passive network that includes a filter capacitance; and

applying a second guard voltage different from the first guard voltage to the at least one guarding electrode; and

measuring a voltage on the filter capacitance for a number of measurements equal to at least one to produce at least one result to determine the measurable capacitance for proximity detection.