All-CMOS high-impedance output buffer for a bus driven by multiple power-supply voltages
US5444397A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Oct 5, 1994 |
| Grant date | Aug 22, 1995 |
| Priority date | — |
| Expiry date | Oct 5, 2014 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03K2217/0018
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
An all-CMOS output buffer drives a bus that can operate at 3 volts and 5 volts. When in a high-impedance state, the output buffer draws little or no current. If the bus is driven to 5 volts by an external device, the high impedance output buffer is in danger of latch-up and distortion of the bus logic level since it only has a 3-volt power supply and does not use a charge pump or an extra 5-volt supply. A biasing circuit couples an N-well that contains p-channel transistors and a driver transistor to the bus driven to 5 volts. Thus the N-well is also driven to 5 volts, the voltage on the bus. The gate of the p-channel driver transistor in the high-impedance output buffer is also coupled to the N-well by another p-channel transistor, raising the gate potential to 5 volts. Thus the gate and body of the p-channel driver transistor is at 5 volts, eliminating reversing current and latch-up problems. A transmission gate isolates the gate of the p-channel driver transistor from the rest of the device's circuitry. The p-channel transistors of the transmission gate, bias circuitry, and driver transistor are located in the N-well, which is biased up to 5 volts only when necessary. Thus durin…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.