Out-of-band signal detection

1. An optical receiver that includes an out-of-band signal detector, the optical receiver comprising:

a photodiode including an anode and a cathode, the photodiode configured to receive an optical in-band signal and an optical out-of-band signal from an optical cable and to generate an electrical signal based on the optical out-of-band signal;

a current to voltage processing circuit that includes a plurality of current mirror circuits, the current to voltage processing circuit electrically coupled to the cathode, and the plurality of current mirror circuits configured to extract a voltage differential signal that represents a modulated out-of-band data signal of from the electrical signal;

a limiting amplifier circuit electrically coupled to the plurality of current mirror circuits and configured to receive the voltage differential signal that represents the modulated out-of-band data signal and to apply a gain to the voltage differential signal that represents the modulated out-of-band data signal to generate an amplified signal including 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 , further comprising a stabilizer circuit electrically coupled between the cathode and the plurality of current mirror circuits, wherein the stabilizer circuit is configured to stabilize a voltage on the cathode.

3. The optical receiver of claim 1 , further comprising an analog-to-digital converter electrically coupled between the limiting amplifier circuit and the demodulation circuit, the analog-to-digital converter is configured to sample the amplified signal.

4. The optical receiver of claim 1 , 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.

5. The optical receiver of claim 4 , further comprising a biasing circuit electrically coupled between the drain of the fourth transistor and a gate and the drain of the third transistor, wherein the biasing circuit is configured to control a voltage and/or a current in the plurality of current mirror circuits.

6. The optical receiver of claim 4 , wherein the electrical signal further includes a direct current portion, wherein the current to voltage processing circuit further comprises a filter circuit electrically coupled to the fourth transistor and the gate and the drain of the third transistor, the filter circuit being configured to extract the modulated out-of-band data signal.

7. The optical receiver of claim 4 , further comprising a signal-to-noise-ratio (SNR) improvement circuit electrically coupled to the second current mirror circuit, wherein the SNR improvement circuit is configured to increase a dynamic direct current input range of the optical receiver.

8. The optical receiver of claim 7 , wherein the SNR improvement circuit includes a first diode and a second diode, wherein the first diode is electrically coupled between a source of the third transistor and a signal ground and the second diode is electrically coupled between a source of the fourth transistor and the signal ground.

9. The optical receiver of claim 4 , further comprising

a first node electrically coupled to the drains of the first and third transistors, a gate of the third transistor, and the limiting amplifier circuit;

a second node electrically coupled to the drains of the second and third transistors and the limiting amplifier circuit;

a first resistive circuit electrically coupled between the first node and the second node;

a second resistive circuit electrically coupled between the first node and a gate of the fourth transistor; and

a capacitive circuit electrically coupled between the gate of the fourth transistor and a signal ground.

10. 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, wherein the voltage differential signal that represents the modulated out-of-band data is based on the difference in signal power levels between the AC portion and the DC portion of the electrical signal;

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

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

11. The method of claim 10 , 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.

12. The method of claim 10 , further comprising generating the electrical signal based on an optical signal.

13. The method of claim 10 , 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.

14. The method of claim 13 , wherein extracting the AC portion of the electrical signal further comprises extracting a difference between the averaged voltage and a voltage of the electrical signal.

15. 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 electrically coupled to the first node and 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, wherein the voltage differential signal is based on the difference in signal power levels between the AC portion and the DC portion of the electrical signal;

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

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

16. The out-of-band signal detector of claim 15 , further comprising a digital demodulation circuit electrically coupled to the analog-to-digital convertor circuit, the digital demodulation circuit is configured to demodulate the modulated out-of-band data included in the amplified signal.

17. The out-of-band signal detector of claim 15 , 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.

18. The out-of-band signal detector of claim 15 , further comprising a biasing circuit configured to control a voltage and/or current in a plurality of current mirror circuits.

19. The out-of-band signal detector of claim 18 , 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 first node and drains of the first, second, third and fourth transistors are electrically coupled to the limiting amplifier circuit.

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

a second node electrically coupled to the drains of the first and third transistors, a gate of the third transistor, and the limiting amplifier circuit;

a third node electrically coupled to the drains of the second and third transistors and the limiting amplifier circuit;

a first resistive circuit electrically coupled between the second node and the third node;

a second resistive circuit electrically coupled between the second node and a gate of the fourth transistor; and

a capacitive circuit electrically coupled between the gate of the fourth transistor and a signal ground.