Out-of-band signal detection

1. An optical receiver comprising:

a photodiode configured to generate an electrical signal based on a received optical out-of-band signal;

a plurality of current mirror circuits configured to extract a voltage differential signal that represents a modulated out-of-band data signal based on the electrical signal;

a limiting amplifier circuit configured to receive the voltage differential signal and to apply a gain to the voltage differential signal to generate an amplified signal that includes the modulated out-of-band data signal; and

a demodulation circuit electrically coupled to the limiting amplifier circuit and configured to demodulate the modulated out-of-band data signal included in the amplified signal.

2. The optical receiver of claim 1 , the photodiode comprising an anode and a cathode, further comprising a stabilizer circuit electrically coupled between the cathode and the plurality of current mirror circuits.

3. The optical receiver of claim 2 , wherein the stabilizer circuit is configured to stabilize a voltage on the cathode.

4. The optical receiver of claim 1 , further comprising an analog-to-digital converter electrically coupled between the limiting amplifier circuit and the demodulation circuit.

5. The optical receiver of claim 4 , wherein the analog-to-digital converter is configured to sample the amplified signal.

6. The optical receiver of claim 2 , wherein the plurality of current mirror circuits include a first current mirror circuit with first and second transistors and a second current mirror circuit with third and fourth transistors, wherein gates of the first and second transistors are electrically coupled to the cathode and drains of the first, second, third and fourth transistors are electrically coupled to the limiting amplifier circuit.

7. The optical receiver of claim 6 , further comprising a biasing circuit electrically coupled between the drain of the fourth transistor and a gate and the drain of the third transistor.

8. The optical receiver of claim 7 , wherein the biasing circuit is configured to control a voltage and/or a current in the plurality of current mirror circuits.

9. The optical receiver of claim 6 , further comprising a filter circuit electrically coupled to the fourth transistor and a gate and the drain of the third transistor.

10. The optical receiver of claim 9 , wherein the electrical signal includes a direct current portion, and the filter circuit is configured to extract the modulated out-of-band data signal.

11. A method to detect an out-of-band signal, the method comprising:

receiving an electrical signal comprising an alternating current (AC) portion and a direct current (DC) portion, wherein the AC portion includes modulated out-of-band data carried by the electrical signal;

extracting the AC portion of the electrical signal from the DC portion of the electrical signal by creating a voltage differential signal that represents the modulated out-of-band data;

applying a gain to the extracted voltage differential signal to generate an amplified signal including the modulated out-of-band data; and

sampling the amplified signal to generate a digital sample that represents the modulated out-of-band data.

12. The method of claim 11 , wherein the voltage differential signal is based on a difference in signal power levels between the AC portion and the DC portion of the electrical signal.

13. The method of claim 11 , wherein an amplitude of the amplified signal is limited to a particular range and varies based on the AC portion of the electrical signal and not based on the DC portion of the electrical signal.

14. The method of claim 13 , wherein the particular range that the amplitude of the amplified signal is limited to is based on a power range that can be received by an analog-to-digital convertor.

15. The method of claim 11 , further comprising generating the electrical signal based on an optical signal.

16. The method of claim 11 , wherein extracting the AC portion of the electrical signal comprises:

averaging a voltage based on a current that includes the modulated out-of-band data carried by the electrical signal to generate an averaged voltage; and

extracting a difference between the averaged voltage and a voltage of the electrical signal.

17. An out-of-band signal detector comprising:

a first node configured to receive an alternating current (AC) portion and a direct current (DC) portion of an electrical signal, wherein the AC portion includes modulated out-of-band data carried by the electrical signal;

a current to voltage processing circuit configured to extract the AC portion of the electrical signal from the DC portion of the electrical signal by creating a voltage differential signal that represents the modulated out-of-band data;

a limiting amplifier circuit electrically configured to receive the extracted voltage differential signal to generate an amplified signal including the modulated out-of-band data; and

an analog-to-digital convertor circuit configured to sample the amplified signal and to generate a digital sample that represents the modulated out-of-band data.

18. The out-of-band signal detector of claim 17 , wherein the voltage differential signal is based on a difference in signal power levels between the AC portion and the DC portion of the electrical signal.

19. The out-of-band signal detector of claim 17 , further comprising:

a digital demodulation circuit configured to demodulate the modulated out-of-band data included in the amplified signal; and

a biasing circuit configured to control a voltage and/or current in a plurality of current mirror circuits.

20. The out-of-band signal detector of claim 17 , wherein the limiting amplifier circuit generates the amplified signal to be within a power range that can be received by the analog-to-digital convertor circuit.