Differential amplifier with accurate input offset voltage

An apparatus comprising:

• a first differential pair configured to receive a differential input signal and a first bias current and provide a first differential current signal;
• a second differential pair coupled to the first differential pair and configured to receive a differential reference signal and provide a second differential current signal, the second differential current signal being subtracted from the first differential current signal to obtain a differential output signal;
• and
• a third differential pair coupled to the second differential pair and configured to receive the differential input signal and provide a second bias current for the second differential pair.

An apparatus comprising:

• means for amplifying a differential input signal to obtain a first differential current signal;
• means for generating a second differential current signal based on a differential reference signal;
• and
• means for subtracting the second differential current signal from the first differential current signal to obtain a differential output signal, the differential output signal being equal to zero when the differential input signal is equal to a target input offset voltage, wherein one transistor in the first unbalanced differential pair is a different size than one transistor in the second unbalanced differential pair and the second differential current signal tracks at least a portion of the first differential current signal.

A method comprising:

• amplifying a differential input signal to obtain a first differential current signal;
• generating a second differential current signal based on a differential reference signal;
• and
• subtracting the second differential current signal from the first differential current signal to obtain a differential output signal, the differential output signal being equal to zero when the differential input signal is equal to a target input offset voltage, wherein one transistor in the first unbalanced differential pair is a different size than one transistor in the second unbalanced differential pair and the second differential current signal tracks at least a portion of the first differential current signal.