Patent ID: 6670829
Filing Date: 2003-12-30
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; an n-channel bus-switch transistor for conducting current between the first and second bus in response to the enable signal; a p-channel bus-switch transistor for conducting current between the first and second bus in response to the enable signal, the p-channel bus-switch transistor having a gate node and a substrate node; a first 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 second connecting transistor coupled to conduct current from the second bus to the substrate node when power is disconnected from the bus switch and the second bus is powered above ground; a third connecting transistor coupled to conduct current from the second bus to an activating node when power is disconnected from the bus switch and the second bus is powered above ground; and a source transistor, having a gate driven by the activating 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 p-channel bus-switch transistor is biased to isolate the first bus from the second bus when power is disconnected from the bus switch and the second bus is powered above ground.