Patent ID: 6608517
Filing Date: 2003-08-19
Classification: H03K

Abstract:
A bus switch comprising:a first bus; a second bus; an enable signal for indicating when the first bus is to be connected to the second bus; a bus-switch transistor for conducting current between the first and second bus in response to the enable signal; a pullup transistor for conducting current between a bias node and the second bus in response to the enable signal, the pullup transistor having a gate node and a substrate node; a connecting transistor coupled to conduct current from the second bus to the gate node when power is disconnected from the bus switch and the second bus is powered above ground; a first inverting transistor coupled to conduct current from the gate node to the substrate node when power is disconnected from the bus switch and the second bus is powered above ground; a source transistor, having a gate driven by the gate node, for conducting current from a power supply to the substrate node when power is connected, but for isolating the substrate node from the power supply when power is disconnected from the bus switch, whereby the pullup transistor is biased to isolate the second bus when power is disconnected from the bus switch and the second bus is powered above ground.