Interference suppression apparatus for a capacitive keyboard
US4543564A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 26, 1982 |
| Grant date | Sep 24, 1985 |
| Priority date | — |
| Expiry date | Mar 26, 2002 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03K2217/96077
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
Apparatus for suppressing interference in a capacitive keyboard. Unconditioned operating signals from receiving lines are passed into a subtractor, which establishes the difference between the signal present on a reference line in the keyboard and supplies, at the output, a conditioned operating signal which is free from any unwanted electromagnetic component which may have entered the structure. In addition, in order to determine which of several keys is supplying the highest signal, operating signals corresponding to particular receiving lines are scanned in sequence to determine which has the highest amplitude. As the operating signal corresponding to each successive key is scanned, its voltage is compared with a previously-stored voltage for an earlier-scanned key. If a higher voltage is detected, the voltage and key address are stored in place of the previously-stored values.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.