Touch entry system with ambient compensation and programmable amplification
US4988983A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 2, 1988 |
| Grant date | Jan 29, 1991 |
| Priority date | — |
| Expiry date | Sep 2, 2008 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06F3/0421
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A touch input device having infrared light beams defined by a plurality of pairs of light emitters and phototransistors is disclosed. A feedback loop containing a programmable amplifier is employed to compensate for the effects of ambient light and for device irregularities. The phototransistor current is first converted to a signal voltage by an operational amplifier and then is input into a low pass filter. The output of the lowpass filter is input into a feedback loop containing a summing amplifier, a programmable amplifier and an integrator. As light emitters and phototransistors are sequentially activated, the feedback loop with the programmable amplifier compares outputs signals in the unactivated state with those input when the light emitters are activated to compensate for ambient conditions and errors.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.