Live-insertion PMOS biasing circuit for NMOS bus switch

A circuit comprising:

• a p-channel pullup transistor having a source coupled to a first supply line, a drain coupled to a second signal line, and a gate driven by a p-gate node, and a bulk terminal coupled to a well node;
• a connecting transistor having a gate driven by a power supply, a source coupled to the second signal line, and a drain coupled to the p-gate node;
• a source transistor having a source coupled to the power supply, a drain coupled to the well node, and a gate coupled to the p-gate node;
• a first inverting transistor having a source coupled to the well node and the source transistor, a drain driving the p-gate node, and a gate coupled to an inverse-enable input;
• and
• a second inverting transistor having a source coupled to a ground, a drain driving the p-gate node, and a gate coupled to the inverse-enable input.

An isolating circuit comprising:

• input means for connecting to a first signal and a second signal;
• disable signal means for indicating when the first signal is to be disconnected to the second signal;
• n-channel isolation transistor means for conducting current between the first and second signal in response to an n-gate;
• p-channel biasing transistor means for conducting current between a fixed voltage and second signal in response to a p-gate, the p-channel biasing transistor means having an N-well;
• connecting transistor means for conducting current from the second signal to the p-gate when power is disconnected from the isolating circuit and the second signal is powered above ground;
• source transistor means, having a gate driven by the p-gate, for conducting current from a power supply to the N-well when power is connected, but for isolating the N-well from the power supply when power is disconnected from the isolating circuit;
• p-channel inverting transistor means, coupled to the disable signal means, for conducting current from the source transistor means to the p-gate;
• and
• n-channel inverting transistor means, coupled to the disable signal means, for conducting current from the p-gate to a ground.