Circuit for measuring photo-current level in fiber optic links

1. An optoelectronic device, comprising:

a photo-diode that generates a photo-current in response to an optical signal;

a pre-amplifier circuit coupled to the photo-diode to detect the photo-current, the pre-amplifier circuit generating a differential output having a first signal and a second signal based on the photo-current; and

a post-amplifier circuit coupled to the pre-amplifier circuit to receive the first signal and the second signal, the post-amplifier circuit comprising:

a first portion coupled to receive the first signal;

a second portion coupled to receive second signal;

a first resistor coupled to the first portion and the second portion;

a second resistor coupled to the first portion and the second portion; and wherein

a current generated in response to a difference between the first signal and the second signal and flowing across the first resistor causes a corresponding current to flow across the second resistor to produce a potential difference that is representative of a difference between a maximum voltage and a minimum voltage of at least one of the first signal and second signal.

2. The optoelectronic device of claim 1 , wherein the first portion includes a first left transistor having:

an first emitter terminal coupled to a first end of the first resistor and a first left constant current source;

a first collector terminal coupled to a left current drain, a second left constant current source, and a third left current source; and

a first base terminal that receives the first signal.

3. The optoelectronic device of claim 2 , wherein the second portion includes a first right transistor having:

a second emitter terminal coupled to a second end of the first resistor and a first right constant current source;

a second collector terminal coupled to a right current drain, a second right constant current source and a third right current source; and

a second base terminal that receives the second signal.

4. The optoelectronic device of claim 3 , wherein the first left constant current source produces a current that is approximately equal to a current produced by the second left constant current source.

5. The optoelectronic device of claim 3 , wherein the first right constant current source produces a current that is approximately equal to a current produced by the second right constant current source.

6. The optoelectronic device of claim 3 , wherein

the left current drain is configured such that a second current flows through said left current drain to the second resistor, said second current equal in magnitude to a difference between a current that flows into the first collector terminal and a current produced by the first left constant current source;

the right current drain is configured such that a third current flows through said right current drain to the second resistor, said third current equal in magnitude to a difference between a current that flows into the second collector terminal and a current produced by the first right constant current source; and

the second current and the third current together form the corresponding current.

7. The optoelectronic device of claim 6 , wherein

the left current source is configured produce a fourth current when the current flowing into the first collector terminal is greater than a current produced by the first left constant current source, said fourth current equal in magnitude to a difference between a current that flows into the first collector terminal and the current produced by the first left constant current source

the right current source is configured produce a fifth current when the current flowing into the second collector terminal is greater than a current produced by the first right constant current source, said fifth current equal in magnitude to a difference between a current that flows into the second collector terminal and the current produced by the first right constant current source.