Automatic threshold voltage adjustment circuit for dense wavelength division multiplexing or packet transport system and method of operating the same

1. An automatic threshold voltage adjustment circuit, comprising:

an amplitude detector configured to detect an amplitude of a received optical signal;

a variable resistor coupled to said amplitude detector and including a field-effect transistor configured to operate in a triad mode to provide a resistance that varies substantially linearly based on said amplitude; and

an operational amplifier coupled to said variable resistor and configured to apply a variable gain based on said resistance to an input threshold voltage to yield an adapted threshold voltage.

2. The circuit as recited in claim 1 wherein said amplitude detector is selected from the group consisting of:

a photodetector, and

a peak level detector.

3. The circuit as recited in claim 1 wherein said field effect transistor is a junction field effect transistor.

4. The circuit as recited in claim 1 wherein said received optical signal is at a single wavelength.

5. The circuit as recited in claim 1 wherein said adapted threshold voltage is provided to a receive chain of an optical receiver.

6. The circuit as recited in claim 1 wherein said circuit forms part of an optical receiver in an optical communication system selected from the group consisting of:

a dense wavelength division multiplexing system, and

a packet transport system.

7. A method of automatically adjusting threshold voltage, comprising:

detecting an amplitude of a received optical signal with an amplitude detector;

providing a resistance that varies substantially linearly based on said amplitude with a variable resistor coupled to said amplitude detector and including a field-effect transistor configured to operate in a triad mode; and

applying a variable gain based on said resistance to an input threshold voltage to yield an adapted threshold voltage with an operational amplifier coupled to said variable resistor.

8. The method as recited in claim 7 wherein said detecting is carried out with one of:

a photodetector, and

a peak level detector.

9. The method as recited in claim 7 wherein said field effect transistor is a junction field effect transistor.

10. The method as recited in claim 7 wherein said received optical signal is at a single wavelength.

11. The method as recited in claim 7 further comprising providing said adapted threshold voltage to a receive chain of an optical receiver.

12. The method as recited in claim 7 wherein said method is carried out in an optical receiver in an optical communication system selected from the group consisting of:

a dense wavelength division multiplexing system, and

a packet transport system.

13. An optical receiver for an optical communication system, comprising:

a receive chain configured to receive an optical signal and derive an electrical signal representing digital data therefrom based on an adapted threshold voltage; and

an automatic threshold voltage adjustment circuit, including:

an amplitude detector configured to detect an amplitude of a received optical signal,

a variable resistor coupled to said amplitude detector and including a field-effect transistor configured to operate in a triad mode to provide a resistance that varies substantially linearly based on said amplitude, and

an operational amplifier coupled to said variable resistor and configured to apply a variable gain based on said resistance to an input threshold voltage to yield said adapted threshold voltage.

14. The optical receiver as recited in claim 13 wherein said amplitude detector is selected from the group consisting of:

a photodetector, and

a peak level detector.

15. The optical receiver as recited in claim 13 wherein said field effect transistor is a junction field effect transistor.

16. The optical receiver as recited in claim 13 wherein said received optical signal is at a single wavelength.

17. The optical receiver as recited in claim 13 wherein said adapted threshold voltage is provided to an operational amplifier in said receive chain.

18. The optical receiver as recited in claim 13 further comprising:

an additional plurality of said optical receivers; and

a demultiplexer coupled to said receiver and said additional plurality of optical receivers and configured to apportion received optical signals thereamong based on wavelengths thereof.

19. The optical receiver as recited in claim 18 wherein said receiver is in a dense wavelength division multiplexing system.

20. The optical receiver as recited in claim 13 wherein said optical receiver is in a packet transport system.