Low leakage electrostatic discharge protection circuit

1. An electrostatic discharge (ESD) protection circuit, comprising:

a silicon control rectifier (SCR)connected between a first voltage rail and a second voltage rail, said SCR comprising a PNP bipolar transistor and an NPN bipolar transistor;

one or more diodes connected in series in a forward conduction direction between said first voltage rail and the source of a p-channel field effect transistor (PFET), the drain of said PFET connected to said second voltage rail through a current trigger device;

a control circuit connected between said first voltage rail and said second voltage rail and connected to the gate of said PFET;

wherein the base of said PNP bipolar transistor is directly connected to said first voltage rail, to the emitter of said PNP bipolar transistor, to the anode of a first diode of said one or more diodes and to the collector of said NPN bipolar transistor;

wherein the base of said NPN bipolar transistor is connected to the drain of said PFET and to the collector of said PNP bipolar transistor; and

wherein the emitter of said NPN bipolar transistor is connected to said second voltage rail.

2. The ESD protection circuit of claim 1 , further including:

a functional circuit sensitive to electrostatic discharge connected between said first and second voltage rails.

3. The ESD protection circuit of claim 1 , wherein said control circuit is configured to turn on said PFET in the event of an ESD event on said first voltage rail.

4. The ESD protection circuit of claim 1 , wherein said control circuit comprises a power on reset circuit.

5. The ESD protection circuit of claim 1 , wherein said control circuit comprises an RC timer.

6. The ESD protection circuit of claim 1 , wherein said current trigger device comprises a resistor.

7. The ESD protection circuit of claim 1 , wherein said first voltage rail is more positive than said second voltage rail and wherein the anode of a first diode of said one or more diodes is connected to said first voltage rail and the cathode of a last diode of said one or more diodes is connected to the source of said PFET.

8. The ESD protection circuit of claim 1 , wherein said one or more diodes comprises five or more diodes connected in series.

9. The ESD protection circuit of claim 1 , wherein a leakage current from said first power rail to said second power rail through said ESD protection circuit is equal to or less than about 3.0 nA at about 3.3 volts or less when said PFET is off.

10. The ESD protection circuit of claim 1 , wherein said control circuit comprises a network of invertors, NFETs, resistors and capacitors.

11. The ESD protection circuit of claim 1 , wherein said control circuit comprises:

a first capacitor, a second capacitor, a third capacitor, a resistor, a first NFET, a second NFET, a first inverters, a second inverter, a third inverter and a fourth inverter; said first, second and third inverters connected between said first and second power rails, said resistor connected between said first power rail and the drain of said first NFET, said first capacitor connected between said first power rail and the drain of said second NFET N 2 and to the input of said second inverter, said second capacitor connected between said second power rail and the input of said first inverter and to the output of said second inverter and to the input of said third inverter, the source of said first NFET connected to the gate of said second NFET, the gate of said first NFET connected to the output of said first inverter, the source of said second NFET connected to said second power rail, the bodies of said first and second NFETs connected to said second power rail, the output of said third inverter connected to the input of said fourth inverter, and the output of said fourth inverter I 4 is the output of said control circuit and is connected to the gate of said PFET.

12. A method of electrostatic discharge (ESD) protection, comprising:

connecting a silicon control rectifier (SCR) between a first voltage rail and a second voltage rail, said SCR comprising a PNP bipolar transistor and an NPN bipolar transistor;

connecting one or more diodes in series in a forward conduction direction between said first voltage rail and the source of a p-channel field effect transistor (PFET);

connecting the drain of said PFET to said second voltage rail through a current trigger device

connecting a control circuit between said first voltage rail and said second voltage rail and to the gate of said PFET;

directly connecting the base of said PNP bipolar transistor to said first voltage rail;

connecting the base of said PNP bipolar transistor to the emitter of said PNP bipolar transistor, to the anode of a first diode of said one or more diodes and to the collector of said NPN bipolar transistor;

connecting the base of said NPN bipolar transistor to the drain of said PFET and to the collector of said PNP bipolar transistor; and

connecting the emitter of said NPN bipolar transistor to said second voltage rail.

13. The method claim 12 , further including:

connecting a functional circuit sensitive to electrostatic discharge between said first and second voltage rails.

14. The method of claim 12 , wherein said control circuit is configured to turn on said PFET in the event of an ESD event on said first voltage rail.

15. The method of claim 12 , wherein said control circuit comprises a power on reset circuit.

16. The method of claim 12 , wherein said control circuit comprises an RC timer.

17. The method of claim 12 , wherein said current trigger device comprises a resistor.

18. The method of claim 12 , wherein said first voltage rail is more positive than said second voltage rail and wherein the anode of a first diode of said one or more diodes is connected to said first voltage rail and the cathode of a last diode of said one or more diodes is connected to the source of said PFET.

19. The method of claim 12 , wherein said one or more diodes comprises five or more diodes connected in series.

20. The method of claim 12 , wherein a leakage current from said first power rail to said second power rail through said SCR, said one or more diodes, said PFET and said current trigger device is equal to or less than about 3.0 nA at about 3.3 volts or less when said PFET is off.

21. The method of claim 12 , wherein said control circuit comprises a network of invertors, NFETs, resistors and capacitors.

22. The method of claim 12 , wherein said control circuit comprises:

a first capacitor, a second capacitor, a third capacitor, a resistor, a first NFET, a second NFET, a first inverters, a second inverter, a third inverter and a fourth inverter; said first, second and third inverters connected between said first and second power rails, said resistor connected between said first power rail and the drain of said first NFET, said first capacitor connected between said first power rail and the drain of said second NFET N 2 and to the input of said second inverter, said second capacitor connected between said second power rail and the input of said first inverter and to the output of said second inverter and to the input of said third inverter, the source of said first NFET connected to the gate of said second NFET, the gate of said first NFET connected to the output of said first inverter, the source of said second NFET connected to said second power rail, the bodies of said first and second NFETs connected to said second power rail, the output of said third inverter connected to the input of said fourth inverter, and the output of said fourth inverter I 4 is the output of said control circuit and is connected to the gate.