Optical receiver having an open loop automatic gain control circuit

An automatic gain control (AGC) circuit configured to sense an input optical power level and to adjust a gain level of amplified electrical signals in accordance with the input optical power level, comprising:

• a resistor configured to receive electrical signals from a photodiode and produce an input optical voltage in proportion to the input optical power level;
• a comparator configured to compare the input optical voltage with a reference voltage and provide a difference voltage;
• a converter coupled to the comparator, wherein the converter receives the difference voltage and outputs two varying voltages, that vary in opposite directions;
• and
• an attenuation circuit configured to receive the two varying voltages from the converter and output an attenuated electrical signal to an output amplification stage, whereby any fluctuation in the input optical voltage is corrected, ensuring a constant output power level,
• wherein the attenuation circuit comprises a first and a second field effect transistor (FET) that each receives a same one of the two varying voltages and a third FET that receives another of the two varying voltages, the first and second FETs electrically coupling the input and output amplification stages and the third FET electrically coupling nodes between respective source and drain electrodes of the first and second FETs.

A method of adjusting a gain level of amplified electrical signals in accordance with an input optical power level of a circuit, the method comprising:

• receiving an input optical voltage in proportions to the input optical power level;
• comparing the input optical voltage with a reference voltage and providing a difference voltage;
• converting the difference voltage into two varying voltages, that vary in opposite directions;
• providing a first one of the two varying voltages to each of a first and a second field effect transistor (FET) and a second one of the two varying voltages to a third FET of an attenuation circuit, wherein the third FET electrically couples nodes between respective source and drain electrodes of the first and second FETs;
• and
• amplifying an output of the attenuation circuit, whereby any fluctuation in the input optical voltage is corrected, ensuring a constant output power level.