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Eliminating the effect of contact resistance in an RC-Sheet sensor

IP.com Disclosure Number: IPCOM000132469D
Publication Date: 2005-Dec-17
Document File: 4 page(s) / 123K

Publishing Venue

The IP.com Prior Art Database

Related People

Paul Routley: INVENTOR [+2]

Abstract

Controlling the potential of a point away from the contact of an RC (resistive-capacitive) sheet sensor device can reduce or eliminate the effects of contact resistance on device performance.

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Eliminating the effect of contact resistance in an RC-Sheet sensor Paul Routley

Eliminating the effect of contact resistance in an RC-Sheet sensor

1. Inventor(s): Paul Routley, David Ely

2. Synaptics Incorporated, Santa Clara, CA, USA

3. Short Summary

Controlling the potential of a point away from the contact of an RC (resistive-capacitive) sheet sensor device can reduce or eliminate the effects of contact resistance on device performance.

Figure 1. Schematic of a contact resistance compensation scheme

4. Some Problems Solved

An RC sheet sensor can be used to detect finger position by measuring the current flowing in a number of electrical contacts held at the same potential and coupled to the RC sheet1. Therefore, any resistance in series with the contacts and driver electronics usually means that the contacts are not held at the same

1 For example, see MicroTouch (now owned by 3M) touch screen products.

Copyright © 2005 Synaptics Incorporated, All Rights Reserved. Page: 1 of 4

Information contained in this publication is provided as-is, with no express or implied warranties, including any warranty of merchantability, fitness for any particular purpose, or non-infringement. Synaptics Incorporated assumes no liability whatsoever for any use of the information contained herein, including any liability for intellectual property infringement. This publication conveys no express or implied licenses to any intellectual property rights belonging to Synaptics or any other party. Synaptics may, from time to time and at its sole option, update the information contained herein without notice.

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Eliminating the effect of contact resistance in an RC-Sheet sensor Paul Routley

potential when different currents flow in different contacts. In general this reduces sensor sensitivity. In addition, if these resistances are not well defined, then any differences between expected and actual resistances will result in systematic errors in calculated finger position.

In many designs, a significant series resistance occurs at the junction between the relatively high conductivity contacts and relatively low conductivity RC sheet material. The effect of this resistance can be compensated for by sensing the potential of the sheet a small distance away from the contact and driving the contact to achieve the required potential at the sensing point. Current can be monitored in the driving contact in the conventional manner, and the sensitivity and accuracy of an ideal zero resistance contact can be achieved.

5. General Description

This invention is in many respects similar to a 'four point probe' measurement that is often used when measuring sheet resistance in the microelectronic industry. With a four point probe measurement, current is injected into the sheet under investigation by two probes, and the potential difference between two other points is measured by another set of probes. Because n...