Equalizing amplifier, receiver using the same and preamplifier

An equalizing amplifier for equalizing an electric signal obtained from a light signal received via an optical transmission path, said equalizing amplifier comprising:

• an AGC circuit generating first and second signals from the electric signal by referring to a threshold voltage, said first and second signals being complementary signals;
• and
• an offset compensation circuit generating a first difference signal based on a difference between said first and second signals, comparing said first difference signal with a first reference signal and outputting, as said threshold voltage, a resultant error signal to said AGC circuit,
• said threshold voltage being varied so that it is located in the center of an amplitude of said electric signal whereby an offset of said AGC circuit can be compensated for,
• wherein said offset compensation circuit comprises a circuit part which performs a level-shift operation on one of said first and second signals output from said AGC circuit and then generates said first difference signal based on the difference between the first and second signals.

An equalizing amplifier for equalizing an electric signal obtained from a light signal received via an optical transmission path, said equalizing amplifier comprising:

• an AGC circuit generating first and second signals from the electric signal by referring to a threshold voltage, said first and second signals being complementary signals;
• and
• an offset compensation circuit generating a first difference signal based on a difference between said first and second signals, comparing said first difference signal with a first reference signal and outputting, as said threshold voltage, a resultant error signal to said AGC circuit,
• said threshold voltage being varied so that it is located in the center of an amplitude of said electric signal whereby an offset of said AGC circuit can be compensated for,
• wherein said first reference signal corresponds to a logic level of one of the first and second signals, and
• wherein said offset compensation circuit comprises:
• a rectifying circuit performing a peak-operation on said first difference signal;
• and
• an error detection circuit comparing a peak-rectified version of said first difference signal with said first reference signal.

An equalizing amplifier for equalizing an electric signal obtained from a light signal received via an optical transmission path, said equalizing amplifier comprising:

• an AGC circuit generating first and second signals from the electric signal by referring to a threshold voltage, said first and second signals being complementary signals;
• and
• an offset compensation circuit generating a first difference signal based on a difference between said first and second signals, comparing said first difference signal with a first reference signal and outputting, as said threshold voltage, a resultant error signal to said AGC circuit,
• said threshold voltage being varied so that it is located in the center of an amplitude of said electric signal whereby an offset of said AGC circuit can be compensated for;
• and
• a level shift circuit which shifts a level of one of the first and second signals so that a first logic level of said first signal coincides with a second logic level of said second signal.

An equalizing amplifier for equalizing an electric signal obtained from a light signal received via an optical transmission path, said equalizing amplifier comprising:

• an AGC circuit generating first and second signals from the electric signal by referring to a threshold voltage, said first and second signals being complementary signals;
• an offset compensation circuit generating a first difference signal based on a difference between said first and second signals, comparing said first difference signal with a first reference signal and outputting, said threshold voltage, a resultant error signal to said AGC circuit,
• said threshold voltage being varied so that it is located in the center of an amplitude of said electric signal whereby an offset of said AGC circuit can be compensated for;
• and
• a gain control circuit which detects a second difference signal based on a difference between the first and second signals, compares said second difference signal with a second reference signal, and outputs, as a gain control signal, a resultant error signal to said AGC circuit;
• and wherein
• the gain control signal controls a gain of the AGC circuit.

The equalizing amplifier as claimed in 12, wherein:

• said AGC circuit has first and second differential amplifiers having different gains;
• the first and second differential amplifiers comprise transistors which receive said electric signal and said threshold voltage;
• and
• said AGC circuit comprises transistors which are connected in parallel with the first and second differential amplifiers and are controlled in accordance with said gain control signal.

A receiver comprising:

• an equalizing amplifier which equalizes an electric signal obtained from a light signal transmitted over an optical transmission path;
• a timing generator which generates a clock signal from timing information contained in said electric signal;
• and
• a decision circuit which makes a decision on an output signal of the equalizing amplifier using said clock signal,
• said equalizing amplifier comprising:
• an AGC circuit generating first and second signals from the electric signal by referring to a threshold voltage, said first and second signals being complementary signals;
• and
• an offset compensation circuit generating a first difference signal based on a difference between said first and second signals, comparing said first difference signal with a first reference signal and outputting, as said threshold voltage, a resultant error signal to said AGC circuit,
• said threshold voltage being varied so that it is located in the center of an amplitude of said electric signal so that an offset of said AGC circuit can be compensated for.

A preamplifier comprising:

• a first transistor amplifying an input signal;
• a second transistor amplifying an output of the first transistor;
• a clamp circuit that includes a resistance element and a third transistor connected in parallel and is provided between an emitter of the second transistor and a base of the first transistor;
• and
• a feedback circuit that is connected to the emitter of the second transistor and applies a variation in an emitter voltage of the second transistor to a base of the third transistor.

A preamplifier comprising:

• a first transistor amplifying an input signal;
• a second transistor amplifying an output of the first transistor;
• a clamp circuit that includes a resistance element and a third transistor connected in parallel and is provided between an emitter of the second transistor and a base of the first transistor;
• and
• an output buffer circuit having a configuration identical to that of another output buffer circuit connected to an input terminal of a following differential amplifier and applying an output signal from the second transistor to another input terminal of said differential amplifier.

An equalizing amplifier for equalizing an electric signal obtained from a light signal received via an optical transmission path, said equalizing amplifier comprising:

• an AGC circuit generating first and second signals from the electric signal by referring to a threshold voltage, said first and second signals being complementary signals;
• and
• an offset compensation circuit generating a first difference signal based on a difference between said first and second signals, comparing said first difference signal with a first reference signal and outputting, as said threshold voltage, a resultant error signal to said AGC circuit,
• said threshold voltage being varied so that it is located in the center of an amplitude of said electric signal whereby an offset of said AGC circuit can be compensated for;
• wherein said offset compensation circuit comprises:
• a first rectifying circuit that performs a peak rectifying operation on said first signal;
• a second rectifying circuit that performs a peak rectifying operation on said second signal;
• and
• an error detecting circuit detecting a difference between a peak-rectified version of said first signal and a peak-rectified version of said second signal, and outputting said first difference signal functioning as said threshold voltage.