Protection circuit

1. A system comprising:

a channel over which signals are transmitted between test equipment and a device under test (DUT); and

limiting circuitry to limit a voltage on the channel, the limiting circuitry comprising a PN-junction device connected to pass current in response to the voltage on the channel exceeding a limit;

wherein the limiting circuitry comprises a positive limiting circuit to protect the DUT, the positive limiting circuit comprising:

a first diode having a first anode and a first cathode, the first anode being electrically connected to the channel;

a second diode comprising the PN-junction device, the second diode having a second anode and a second cathode, the second anode being electrically connected to the first cathode; and

an amplifier having a first input electrically connected to the second anode and a second input electrically connected to the second cathode.

2. The system of claim 1 , wherein a first voltage is at the second cathode and a second voltage is at the second anode, the second voltage being based on the voltage on the channel, the second diode conducting in response to the second voltage exceeding the first voltage.

3. The system of claim 2 , further comprising:

a voltage generator to provide the first voltage to the second cathode, the first voltage being adjustable.

4. The system of claim 2 , wherein conduction of the second diode causes current to pass through the second diode resulting in a voltage drop across the second diode that is relayed to the amplifier via the first and second inputs, the amplifier for outputting a signal based on the voltage drop.

5. The system of claim 4 , further comprising:

a comparator comprising a third input and a fourth input, the third input for receiving a threshold value and the fourth input for receiving the signal from the amplifier, the comparator to output an indication of a fault based on a comparison of the signal to the threshold.

6. The system of claim 1 , wherein the channel is a first channel; and

wherein the system further comprises:

a second channel over which signals are transmitted between the test equipment and the device under test (DUT); and

second limiting circuitry to limit a voltage on the second channel, the second limiting circuitry comprising a second PN-junction device connected to pass current in response to the voltage for the second channel exceeding a limit.

7. The system of claim 1 , wherein limiting the voltage on the channel comprises limiting an amount of positive voltage on the channel.

8. A system comprising:

a channel over which signals are transmitted between test equipment and a device under test (DUT); and

limiting circuitry to limit a voltage on the channel, the limiting circuitry comprising a PN-junction device connected to pass current in response to the voltage on the channel exceeding a limit;

wherein the limiting circuitry comprises a negative limiting circuit to protect the test equipment, the negative limiting circuit comprising:

a first diode having a first anode and a first cathode, the first cathode being electrically connected to the channel;

a second diode comprising the PN-junction device, the second diode having a second anode and a second cathode, the second cathode being electrically connected to the first anode; and

an amplifier having a first input electrically connected to the second anode and a second input electrically connected to the second cathode.

9. The system of claim 8 , wherein a first voltage is at the second anode and a second voltage is at the second cathode, the second diode conducting in response to the first voltage exceeding the second voltage.

10. The system of claim 9 , further comprising:

a voltage generator to provide the first voltage to the second anode, the first voltage being adjustable.

11. The system of claim 9 , wherein conduction of the second diode causes current to pass through the second diode resulting in a voltage drop across the second diode that is relayed to the amplifier via the first and second inputs, the amplifier for outputting a signal based on the voltage drop.

12. The system of claim 11 , further comprising:

a comparator comprising a third input and a fourth input, the third input for receiving a threshold value and the fourth input for receiving the signal from the amplifier, the comparator to output an indication of a fault based on a comparison of the signal to the threshold.

13. The system of claim 8 , wherein the channel is a first channel; and

wherein the system further comprises:

a second channel over which signals are transmitted between the test equipment and the device under test (DUT); and

second limiting circuitry to limit a voltage on the second channel, the second limiting circuitry comprising a second PN-junction device connected to pass current in response to the voltage for the second channel exceeding a limit.

14. The system of claim 8 , wherein limiting the voltage on the channel comprises limiting an amount of negative voltage on the channel.

15. The system of claim 14 , wherein limiting an amount of negative voltage on the channel comprises ensuring that an absolute value of the negative voltage does not exceed a maximum absolute value.

16. A system comprising:

test equipment to test a device under test (DUT) by sending and receiving signals over a channel electrically connected to the DUT;

a first limiting circuit to protect the DUT from an over-voltage on the channel, the first limiting circuit comprising a first PN-junction device to pass current in response to the over-voltage on the channel; and

a second limiting circuit to protect the test equipment from an under-voltage on the channel, the second limiting circuit comprising a second PN-junction device to pass current in response to the under-voltage on the channel;

wherein the first limiting circuit comprises:

a first diode having a first anode and a first cathode, the first anode being electrically connected to the channel;

a second diode comprising the first PN-junction device, the second diode having a second anode and a second cathode, the second anode being electrically connected to the first cathode;

an amplifier having a first input electrically connected to the second anode and a second input electrically connected to the second cathode; and

a comparator comprising a third input and a fourth input, the third input for receiving a threshold value and the fourth input for receiving a signal from the amplifier, the comparator to output an indication of a fault based on a comparison of the signal to the threshold.

17. The system of claim 16 , wherein the second PN-junction device comprises a diode.

18. The system of claim 16 , wherein the second PN-junction device comprises a transistor.

19. The system of claim 16 , wherein the test equipment comprises pin electronics, the second limiting circuit to protect the pin electronics.

20. The system of claim 16 , wherein protecting the DUT from an over-voltage on the channel comprises limiting an amount of positive voltage on the channel; and

wherein protecting the test equipment from an under-voltage on the channel comprises limiting an amount of negative voltage on the channel.

21. The system of claim 20 , wherein limiting an amount of negative voltage on the channel comprises ensuring that an absolute value of the negative voltage does not exceed a maximum absolute value.

22. A system comprising:

test equipment to test a device under test (DUT) by sending and receiving signals over a channel electrically connected to the DUT;

a first limiting circuit to protect the DUT from an over-voltage on the channel, the first limiting circuit comprising a first PN-junction device to pass current in response to the over-voltage on the channel; and

a second limiting circuit to protect the test equipment from an under-voltage on the channel, the second limiting circuit comprising a second PN-junction device to pass current in response to the under-voltage on the channel;

wherein the second limiting circuit comprises:

a first diode having a first anode and a first cathode, the first cathode being electrically connected to the channel;

a second diode comprising the second PN-junction device, the second diode having a second anode and a second cathode, the second cathode being electrically connected to the first anode;

an amplifier having a first input electrically connected to the second anode and a second input electrically connected to the second cathode; and

a comparator comprising a third input and a fourth input, the third input for receiving a threshold value and the fourth input for receiving a signal from the amplifier, the comparator to output an indication of a fault based on a comparison of the signal to the threshold.

23. The system of claim 22 , wherein the first PN-junction device comprises a diode.

24. The system of claim 22 , wherein the test equipment comprises pin electronics, the second limiting circuit to protect the pin electronics.

25. The system of claim 22 , wherein the first PN-junction device comprises a transistor.

26. The system of claim 22 , wherein protecting the DUT from an over-voltage on the channel comprises limiting an amount of positive voltage on the channel; and

wherein protecting the test equipment from an under-voltage on the channel comprises limiting an amount of negative voltage on the channel.

27. The system of claim 26 , wherein limiting an amount of negative voltage on the channel comprises ensuring that an absolute value of the negative voltage does not exceed a maximum absolute value.