Switch closure sensing circuit
US4318087A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 8, 1980 |
| Grant date | Mar 2, 1982 |
| Priority date | — |
| Expiry date | Sep 8, 2000 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03K17/9618
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A keyboard system includes a row and a column matrix of electrically isolated conductors with a key switch at each intersection which is effective, when closed, to electrically connect the associated intersecting row and column conductors. The conduction path of a column transistor is connected between each column conductor and a first power terminal and the gate-to-source region of a respective row transistor is connected between each row conductor and a second power terminal. The column transistors are turned-on prior to any switch closure. Therefore, when a switch is closed, its associated column transistor provides a very low impedance, low voltage drop, path between the first power terminal and the row transistor connected to the row conductor associated with the switch. The row transistor is then turned-on if the operating voltage applied between the first and second power terminal exceeds the threshold voltage of the row transistor. A normally off pulse generating system is coupled between the drains of the row transistors and the control electrodes of the column transistors. The pulse operating system is activated in response to a switch closure and sequentially scans the c…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.