Combined active and passive high-power RF protection circuit

1. For use in an electronic system including circuitry that is sensitive to a high frequency EMI/RF signal, a protection circuit comprising:

passive mode circuitry operational when the electronic system is powered off, the passive mode circuitry comprising:

at least one PIN diode coupled between a transmission line and ground, wherein the transmission line is coupled between an input of the electronic system and an antenna that receives the high frequency EMI/RF signal and wherein the at least one PIN diode turns on when the high frequency EMI/RF signal on the transmission line exceeds a passive limiter threshold level of the at least one PIN diode,

a switch that is closed in a passive mode, the switch having a first pole and a second pole, wherein the second pole is coupled to ground, and

an inductor coupled between the transmission line and the first pole of the switch; and

active mode circuitry operational when the electronic system is powered on, the active mode circuitry comprising:

an RF threshold detector for detecting a signal level on the transmission line and determining when the high frequency EMI/RF signal on the transmission line exceeds a predetermined detector threshold level, and

a current driver that is turned on when the RF threshold detector determines that the high frequency EMI/RF signal on the transmission line exceeds the predetermined detector threshold level,

wherein the switch is open in an active mode and wherein the current driver, when turned on, applies a DC bias current to the at least one PIN diode, the DC bias current activating the at least one PIN diode.

2. The protection circuit as set forth in claim 1 , wherein, when the switch is open in the active mode, the passive mode circuitry is disabled.

3. The protection circuit as set forth in claim 1 , wherein the RF threshold detector is coupled to the transmission line by an RF directional coupler.

4. The protection circuit as set forth in claim 1 , wherein the current driver applies the DC bias current to the at least one PIN diode through the inductor.

5. An electronic system comprising:

an antenna;

a transmission line coupled to the antenna;

RF electronics circuitry coupled to the transmission line that is sensitive to a high frequency EMI/RF signal on the transmission line; and

a protection circuit comprising:

passive mode circuitry operational when the electronic system is powered OFF, the passive mode circuitry comprising:

at least one PIN diode coupled between the transmission line and ground, wherein the at least one PIN diode turns on when the high frequency EMI/RF signal on the transmission line exceeds a passive limiter threshold level of the at least one PIN diode,

a switch that is closed in a passive mode, the switch having a first pole and a second pole, wherein the second pole is coupled to ground, and

an inductor coupled between the transmission line and the first pole of the switch; and

active mode circuitry operational when the electronic system is powered ON, the active mode circuitry comprising:

an RF threshold detector for detecting a signal level on the transmission line and determining when the high frequency EMI/RF signal on the transmission line exceeds a predetermined detector threshold level,

a current driver that is turned on when the RF threshold detector determines that the high frequency EMI/RF signal on the transmission line exceeds the predetermined detector threshold level;

wherein the switch is open in an active mode and wherein the current driver, when turned on, applies a DC bias current to the at least one PIN diode, the DC bias current activating the at least one PIN diode.

6. The electronic system as set forth in claim 5 , wherein, when the switch is open in the active mode, the passive mode circuitry is disabled.

7. The electronic system as set forth in claim 5 , wherein the RF threshold detector is coupled to the transmission line by an RF directional coupler.

8. The electronic system as set forth in claim 5 , wherein the current driver applies the DC bias current to the at least one PIN diode through the inductor.

9. The electronic system as set forth in claim 5 , wherein the closed switch and the inductor provide a DC return path for charge generated in the at least one PIN diode by the high frequency EMI/RF signal.

10. The electronic system as set forth in claim 5 , wherein the at least one PIN diode comprises a first PIN diode and a second diode.

11. The electronic system as set forth in claim 10 , wherein the first diode has a higher current capacity than the second diode.

12. The electronic system as set forth in claim 11 , wherein the second diode has a faster switching speed than the first diode.

13. The electronic system as set forth in claim 12 , wherein the first and second diodes are coupled to the transmission line and separated by approximately a quarter wavelength, wherein the wavelength is in the medium of the transmission line.

14. The protection circuit as set forth in claim 1 , wherein the closed switch and the inductor provide a DC return path for charge generated in the at least one PIN diode by the high frequency EMI/RF signal.

15. The protection circuit as set forth in claim 1 , wherein the at least one PIN diode comprises a first PIN diode and a second diode.

16. The protection circuit as set forth in claim 15 , wherein the first diode has a higher current capacity than the second diode.

17. The protection circuit as set forth in claim 16 , wherein the second diode has a faster switching speed than the first diode.

18. The protection circuit as set forth in claim 17 , wherein the first and second diodes are coupled to the transmission line and separated by approximately a quarter wavelength, wherein the wavelength is in the medium of the transmission line.