Surge protection circuit

1. A surge protection circuit comprising

an input port for receiving an input voltage;

an energy release cell having a first terminal coupled to the input port, a second terminal coupled to ground, and a control terminal coupled to the input port via a first switch device and to the ground via a second switch device;

the surge protection circuit being adapted to close the first switch device to enable a current to flow from the input port to ground through the energy release cell upon occurrence of a positive voltage surge and to close the second switch device to enable a current to flow from ground to the input port through the energy release cell upon occurrence of a negative voltage surge;

wherein the first switch device comprises a first switch coupled to a second switch, the first switch and the second switch having a common source node, and a common gate node, and wherein body diodes of the first switch and the second switch are connected back to back.

2. The surge protection circuit as claimed in claim 1 , wherein the positive voltage surge occurs when the input voltage rises with a rising slew rate greater than a rising slew rate threshold or when the input voltage rises above a positive voltage threshold for a particular rising slew rate; and wherein the negative voltage surge occurs when the input voltage decreases with a falling slew rate greater than a falling slew rate threshold or when the input voltage decreases below a negative voltage threshold for a particular falling slew rate.

3. The surge protection circuit as claimed in claim 2 , comprising

a first surge cell adapted to provide a first signal to close the first switch device upon occurrence of the positive voltage surge; and

a second surge cell adapted to provide a second signal to close the second switch device upon occurrence of the negative voltage surge.

4. The surge protection circuit as claimed in claim 1 , wherein the first switch device comprises a first Zener diode coupled to the common source node and to a gate terminal of the first and second switches.

5. The surge protection circuit as claimed in claim 1 , wherein the second switch device comprises a third switch coupled to a fourth switch.

6. The surge protection circuit as claimed in claim 5 , wherein the fourth switch has a control terminal coupled to ground via a second Zener diode.

7. The surge protection circuit as claimed in claim 3 , wherein the energy release cell comprises a fifth switch coupled to a sixth switch.

8. The surge protection circuit as claimed in claim 7 , wherein the fifth switch and the sixth switch are power switches.

9. The surge protection circuit as claimed in claim 7 , wherein the first surge cell comprises a first capacitor.

10. The surge protection circuit as claimed in claim 7 , wherein the second surge cell comprises a second capacitor.

11. The surge protection circuit as claimed in claim 9 , wherein the rising slew rate threshold and the positive voltage threshold are defined by the first capacitor and a size of the fifth switch.

12. The surge protection circuit as claimed in claim 10 ; wherein the falling slew rate threshold and the negative voltage threshold are defined by the second capacitor and a size of the sixth switch.

13. The surge protection circuit as claimed in claim 1 , further comprising a biasing circuit coupled to the energy release cell, the biasing circuit being adapted to bias a substrate to the input voltage or to ground.

14. The surge protection circuit as claimed in claim 13 , wherein the biasing circuit comprises a seventh switch coupled to an eighth switch; wherein the seventh switch has a control terminal coupled to ground and wherein the eighth switch has a control terminal coupled to the input port.

15. The surge protecting circuit as claimed in claim 14 , wherein the seventh and eight switches have a common node coupled to the energy release cell.

16. A device comprising a surge protection circuit as claimed in claim 1 .

17. A method of protecting against a surge, the method comprising

receiving an input voltage at an input port;

providing an energy release cell having a first terminal coupled to the input port, a second terminal coupled to ground, and a control terminal coupled to the input port via a first switch device and to the ground via a second switch device;

wherein the first switch device comprises a first switch coupled to a second switch, the first switch and the second switch having a common source node, and a common gate node, and wherein body diodes of the first switch and the second switch are connected back to back;

upon occurrence of a positive voltage surge, closing the first switch device to enable a current to flow from the input port to ground through the enemy release cell; and

upon occurrence of a negative voltage surge, closing the second switch device to enable a current to flow from ground to the input port through the energy release cell.

18. The method as claimed in claim 17 , wherein the positive voltage surge occurs when the input voltage rises with a rising slew rate greater than a rising slew rate threshold or when the input voltage rises above a positive voltage threshold for a particular rising slew rate; and wherein the negative voltage surge occurs when the input voltage decreases with a falling slew rate greater than a falling slew rate threshold or when the input voltage decreases below a negative voltage threshold for a particular falling slew rate.