Signal switch with reduced on resistance and undershoot protection

An electronic switch applies ground potential to the backgate of a MOS pass transistor when the transistor is in the off state and the switch is open, during normal conditions. When the transistor is switched to the on state and the switch is closed, the gate voltage is applied to the backgate of the pass transistor in order to reduce the threshold voltage and the on resistance. During an undershoot condition, the gate of the pass transistor is connected to the negative voltage applied to an input port and this voltage is also connected to the backgate of the pass transistor to prevent the pass transistor from being biased on or the parasitic NPN transistor from being biased on and transmitting the input glitch to the output.