| 摘要 |
A tristate driver interfaces a 3.3 volt digital circuit to a bus that supports both 3.3 and 5.0 volt digital signals. In one embodiment, the pullup circuit path (230) includes a P-channel MOSFET which is backgated by a backgate voltage generator (250) and gated by a gate voltage generator that receives its drive voltage from a comparator and is controlled by an enable circuit. The pulldown circuit path (240) includes an N-channel MOSFET which is controlled by the enable circuit. Current leakage through the pullup circuit is minimized when overvoltage occurs on the bus by suitably gating and backgating the pullup MOSFET. In another embodiment, two MOSFETs are used in the pullup circuit (230). Both are backgated by a backgate voltage generator, while one is gated by a gate voltage generator that receives its drive voltage from the bus while the other is controlled by an enable circuit. The pulldown circuit path (240) includes an N-channel MOSFET which is controlled by the enable circuit. Current leakage through the pullup circuit is minimized when overvoltage occurs on the bus by suitably gating and backgating the pullup MOSFETs. The tristate driver is a general output driver having other applications as well, including application as a voltage driver. |
