Differential amplifier with gain linearization through transconductance compensation

A differential amplifier, comprising:

• an emitter follower pair, including a first transistor and a second transistor, operative to receive an input differential voltage signal for shifting the input differential voltage signal to develop a shifted differential voltage signal;
• a first differential pair, including a third transistor and a fourth transistor, configured to feed a first differential current inversely to the emitter follower pair such that a transconductances of the first transistor and the second transistor changes to compensate for changes in transconductances of the fourth and third transistors, respectively;
• a main differential amplifier, including a fifth transistor with an emitter, a sixth transistor with an emitter, and a first resistor and a second resistor coupled in series between the emitters of the fifth and sixth transistors, wherein the main differential amplifier is coupled to receive the shifted differential voltage signal and being configured to amplify the shifted differential voltage signal to generate an output voltage signal;
• wherein the first, second, third, fourth, fifth, and sixth transistors are bipolar junction transistors, each transistor having a base, a collector, and an emitter;
• and
• wherein the emitters of the first and second transistors are coupled to the bases of the third and fourth transistors, respectively, wherein the third and fifth transistors are coupled in parallel at their bases and emitters, and wherein the fourth and sixth transistors are coupled in parallel at their bases and emitters.

A differential amplifier, comprising:

• an emitter follower pair, including a first transistor and a second transistor, operative to receive an input differential voltage signal for shifting the input differential voltage signal to develop a shifted differential voltage signal;
• a first differential pair, including a third transistor and a fourth transistor, configured to feed a first differential current inversely to the emitter follower pair such that a transconductance of the emitter follower pair changes inversely to compensate for a change in a transconductance of the first differential pair;
• a main differential amplifier including:
• a second differential pair including a fifth transistor and a sixth transistor, wherein the second differential pair is adapted to receive the shifted differential voltage to generate the output signal;
• a first resistor and a second resistor coupled in series between the emitters of the fifth and sixth transistors, the first and second resistor being coupled to each other at a junction;
• a first current source coupled to the junction for providing a current through the first and second resistors;
• and
• a first load resistor and a second load resistor coupled to the collectors of the fifth and sixth transistors, respectively;
• wherein the main differential amplifier is coupled to receive the shifted differential voltage signal and being configured to amplify the shifted differential voltage signal to generate an output voltage signal;
• wherein the first, second, third, fourth, fifth, and sixth transistors are bipolar junction transistors, each transistor having a base, a collector, and an emitter;
• wherein the emitters of the first and second transistors are coupled to the bases of the third and fourth transistors, respectively, wherein the third and fifth transistors are coupled in parallel at their bases and emitters, and wherein the fourth and sixth transistors are coupled in parallel at their bases and emitters;
• and
• wherein the transconductances of the first transistor and the second transistor change to compensate for changes in transconductances of the fourth and third transistors, respectively.

A transconductance compensating circuit for a differential amplifier having a main differential pair, comprising:

• an emitter follower pair operative to receive an input differential voltage signal for shifting the input differential voltage signal to develop a shifted differential voltage signal;
• a first differential pair configured to feed a first differential current inversely to the emitter follower pair such that a transconductance of the emitter follower pair changes inversely to compensate for a change in a transconductance of the first differential pair;
• and
• wherein the main differential pair includes a second differential pair including a fifth transistor with an emitter, a sixth transistor with an emitter, wherein a first resistor and a second resistor are coupled in series between the emitters of the fifth and sixth transistors, and wherein the second differential pair is adapted to receive the shifted differential voltage signal to generate an output signal.

A method for compensating variations in transconductance of a differential amplifier, the method comprising:

• receiving, by a pair of emitter follower transistors, a differential input voltage;
• providing, by a differential pair of transistors, a compensating differential current inversely to the emitter follower transistors, wherein each of the differential pair of transistors has a first terminal, wherein a first resistor and a second resistor are coupled in series between the first terminals of the differential pair of transistors;
• changing a transconductance of the emitter follower transistors inversely to compensate for a change in a transconductance of the differential pair transistors;
• and
• shifting, by the emitter follower pair of transistors, the DC voltage level of the differential input voltage by a specified voltage in accordance with the change in the transconductance of the emitter follower pair transistors.

A differential amplifier, comprising:

• an emitter follower pair operative to receive an input differential voltage signal for shifting the input differential voltage signal to develop a first shifted differential voltage signal;
• a first differential pair, including a third transistor and a fourth transistor, configured to feed a first differential current inversely to the emitter follower pair such that a transconductance of the emitter follower pair changes inversely to compensate for a change in a transconductance of the first differential pair;
• a second emitter follower pair coupled to receive the first shifted differential voltage signal for shifting the shifted differential voltage signal to develop a second shifted differential voltage signal;
• and
• a main differential amplifier, including a second differential pair which includes a fifth transistor and a sixth transistor, coupled to receive the second shifted differential voltage signal and being configured to amplify the second shifted differential voltage signal to generate an output voltage signal.