Constant transconductance differential amplifier

A differential amplifier comprising:

• a first differential amplifying unit for generating a difference between first and second output currents in proportion to a difference between first and second input voltages;
• a second differential amplifying unit for generating a difference between third and fourth output currents in proportion to a difference between third and fourth input voltages;
• a first level shifter for maintaining a constant difference in an offset voltage between the first input voltage and the third input voltage;
• a second level shifter for maintaining a constant difference in offset voltage between the second input voltage and the fourth input voltage;
• a current switch connected between the first and second differential amplifying units, wherein the current switch is adapted to divide a common-mode input range associated with the first and second differential amplifying units;
• and
• a first constant current source for maintaining a constant sum of the first and second output currents of the first differential amplifying unit and a constant sum of the third and fourth output currents of the second differential amplifying unit, wherein a first output current terminal of the first differential amplifying unit is connected to a second output current terminal of the second differential amplifying unit to form a third output current terminal, and wherein a fourth output current terminal of the first differential amplifying unit is connected to a fifth output current terminal of the second differential amplifying unit to form a sixth output current terminal.