Overvoltage protection circuit for bidirectional transmission gate

A transmission gate for controllably providing a conductivity path between a first port and a second port comprising:

• a controlled switching device having a first input/output electrode coupled to said first port, a second input/output electrode coupled to said second port, and a control electrode adapted to receive a control input for controlling conductivity between said first and second input/output electrodes;
• a controlled clamping device having a first electrode coupled to said first port, a second electrode coupled to the control electrode of said controlled switching device, and a control electrode coupled to receive a control voltage for controlling conductivity between said first and second electrodes of said controlled clamping device, and thereby, during an overvoltage condition, application to said control electrode of said controlled switching device of a voltage substantially corresponding to a voltage applied to said first port;
• and
• a clamping control device coupled in circuit with the control electrode of said clamping device, and a terminal to which said control voltage for controlling conductivity between said first and second electrodes of said controlled clamping device is applied, and being operative to controllably enable the operation of said clamping device in accordance with a voltage applied to said second port.

In a transmission gate for controllably providing a conductivity path between a first port and a second port, said transmission gate including a controlled switching device having a first input/output electrode coupled to said first port, a second input/output electrode coupled to said second port, a body coupled through a diode to a power supply terminal to which a supply voltage is applied, and a control electrode adapted to receive a control input for controlling conductivity between said first and second input/output electrodes, the improvement comprising:

• a first controlled clamping device having a first electrode coupled to said first port, a second electrode coupled to the control electrode of said controlled switching device, and a control electrode coupled to receive a control voltage for controlling conductivity between said first and second electrodes of said first controlled clamping device, and thereby application to said control electrode of said controlled switching device of a voltage substantially corresponding to a voltage applied to said first port during an overvoltage event;
• and
• a first clamping control device coupled in circuit with the control electrode of said first controlled clamping device, and a terminal to which said control voltage for controlling conductivity between said first and second electrodes of said first controlled clamping device is applied, and being operative to controllably enable the operation of said first controlled clamping device in accordance with a voltage applied to said second port.