Negative voltage detection and voltage surge protection

1. A circuit comprising:

a reference current generator configured to generate a first current signal representative of a threshold voltage;

a voltage selector configured to:

select a lower voltage of a supply voltage of the circuit and an externally supplied voltage; and

provide the selected voltage to a current comparator as a received voltage; and

the current comparator being configured to:

mirror the first current signal;

generate a second current signal representative of the received voltage;

compare the second current signal to the first current signal; and

provide a detection signal at a first logic value to indicate that the received voltage is below the threshold voltage when the comparison of the second current signal with the first current signal indicates that the received voltage is less than the threshold voltage.

2. The circuit of claim 1 , wherein the threshold voltage is a negative threshold voltage.

3. The circuit of claim 1 , wherein the voltage selector includes a voltage clamp configured to clamp the received voltage to the supply voltage of the circuit when the externally supplied voltage exceeds the supply voltage of the circuit.

4. The circuit of claim 3 , wherein the voltage clamp includes a Zener diode.

5. The circuit of claim 1 , wherein the threshold voltage is a first threshold voltage, the circuit further comprising an enable circuit configured to generate an enable signal to enable the reference current generator if the received voltage is less than a second threshold voltage, the second threshold voltage being greater than the first threshold voltage.

6. The circuit of claim 5 , wherein the current comparator is a first current comparator, the enable circuit including a second current comparator configured to generate the enable signal based on a comparison of the second current signal representative of the received voltage and a third current signal representative of the second threshold voltage.

7. The circuit of claim 1 , wherein the threshold voltage is a first threshold voltage,

the reference current generator being further configured, in response to the detection signal indicating that the received voltage is less than the first threshold voltage, to generate a third current signal representative of a second threshold voltage, the second threshold voltage being greater than the first threshold voltage, and

the current comparator being further configured to:

mirror the third current signal;

compare the second current signal representative of the received voltage to the third current signal; and

in response to the comparison of the second current signal with the third current signal indicating that the received voltage is greater than the second threshold voltage:

provide the detection signal at a second logic value to indicate that the received voltage is greater than the second threshold voltage; and

disable the current comparator.

8. A circuit comprising:

a first current comparator configured to generate an enable signal based on a comparison of a first current signal representative of a received voltage and a second current signal representative of a first threshold voltage;

a reference current generator configured to, in response to the enable signal, generate a third current signal representative of a second threshold voltage, the second threshold voltage being less than the first threshold voltage; and

a second current comparator configured to:

mirror the third current signal;

compare the third current signal to the first current signal; and

provide a detection signal at a first logic value to indicate that the received voltage is below the second threshold voltage when the comparison of the third current signal with the first current signal indicates that the received voltage is less than the second threshold voltage.

9. The circuit of claim 8 , wherein the first threshold voltage and the second threshold voltage are, respectively, a first negative threshold voltage and a second negative threshold voltage.

10. The circuit of claim 8 , further comprising a voltage selector configured to:

select a lower voltage of a supply voltage of the circuit and an externally supplied voltage; and

provide the selected voltage to the current first current comparator and the second current comparator as the received voltage.

11. The circuit of claim 10 , wherein the voltage selector includes a voltage clamp configured to clamp the received voltage to the supply voltage of the circuit when the externally supplied voltage exceeds the supply voltage of the circuit.

12. The circuit of claim 8 , wherein:

the reference current generator is further configured, in response to the detection signal indicating that the received voltage is less than the second threshold voltage, to generate a third current signal representative of a third threshold voltage, the third threshold voltage being greater than the second threshold voltage, and

the current comparator being further configured to:

mirror the third current signal;

compare the first current signal representative of the received voltage to the third current signal; and

if comparing the first current signal with the third current signal indicates that the received voltage is greater than the third threshold voltage:

provide the detection signal at a second logic value to indicate that the received voltage is greater than the third threshold voltage; and

provide a disable signal to the current comparator, the disable signal disabling the current comparator.

13. A method of operating a circuit, the method comprising:

generating, by a current generator, a first current signal representative of a first threshold voltage;

mirroring, by a current comparator, the first current signal;

generating, by the current comparator, a second current signal representative of a received voltage;

comparing, by the current comparator, the second current signal to the first current signal;

providing, by the current comparator, a detection signal at a first logic value to indicate that the received voltage is below the first threshold voltage when the comparing of the second current signal with the first current signal indicates that the received voltage is less than the first threshold voltage; and

generating an enable signal to enable the current generator in response to the received voltage being less than a second threshold voltage, the second threshold voltage being greater than the first threshold voltage.

14. The method of claim 13 , wherein the first threshold voltage is a negative threshold voltage.

15. The method of claim 13 , further comprising:

selecting a lower voltage of a supply voltage of the circuit and an externally supplied voltage; and

providing the selected voltage to the current comparator as the received voltage.

16. The method of claim 15 , further comprising clamping the received voltage to the supply voltage of the circuit when the externally supplied voltage exceeds the supply voltage of the circuit.

17. The method of claim 13 , wherein the current comparator is a first current comparator, the method further comprising, generating, by a second current comparator, the enable signal based on a comparison of the second current signal representative of the received voltage and a third current signal representative of the second threshold voltage.

18. The method of claim 13 , the method further comprising:

generating, by the current generator in response to the detection signal indicating that the received voltage is less than the first threshold voltage, a third current signal representative of a third threshold voltage, the third threshold voltage being greater than the first threshold voltage,

mirroring, by the current comparator, the third current signal;

comparing, by the current comparator, the second current signal representative of the received voltage to the third current signal; and

if comparing the second current signal with the third current signal indicates that the received voltage is greater than the third threshold voltage:

providing the detection signal at a second logic value to indicate that the received voltage is greater than the third threshold voltage; and

disabling the current comparator.