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Browse Prior Art Database

Touch Sensitive Input Device

IP.com Disclosure Number: IPCOM000091734D
Original Publication Date: 1968-May-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Harper, TP: AUTHOR

Abstract

The integrated, touch-sensitive input device provides input data in response to contact of a capacitor plate. The entire circuit can be incorporated on a single integrated chip.

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Touch Sensitive Input Device

The integrated, touch-sensitive input device provides input data in response to contact of a capacitor plate. The entire circuit can be incorporated on a single integrated chip.

Clock 12 generates timing pulses at a rate determined by an external clock EXT or by an externally connected capacitor C2. The clock pulses, under control of Storage-Shift Register 10 are applied to the gate of Q1. The latter is used as a switching device to constantly move the source of Q3 from zero to a negative potential as determined by the effective resistance of Q4. Q5 acts as a load and provides a minimum bias path for the drain of Q1. Q2 is a high-resistance device that provides a charge-discharge path for the gate-to-source capacitance of Q3. Q4 provides a bias potential for the drain of Q3.

In a normal state, when C1 is absent, the gate of Q3 moves almost in phase with its own source. A positive-going parasitic pulse appears at point A, the drain of Q3, each time its source is driven towards ground. This pulse is of very short duration.

If C1 is established either by human touch or mechanical devices, a high- capacitive load is presented to the gate of Q3 which prevents the gate from moving in phase with its source. The gate is then held near -Vc and the drain of Q3 produces pulses of approximately the same duration as those presented at its source. The pulses present on the drain of Q3 are applied to devices Q6 and Q7. The latter, in combination wit...