Voltage amplifier for constant voltage biasing and amplifying signals from a MR sensor

A circuit having a first constant current source for simultaneously biasing, and amplifying signals produced by, a magnetoresistive sensor having a steady-state resistance value, said circuit comprising:

• a bias voltage for the magnetoresistive sensor having constant time average value;
• an input stage, having at least two transistors coupled in a first differential pair configuration and having the magnetoresistive sensor coupled between the bases thereof, and coupled to the first constant current source, for amplifying voltage deviations from said constant time average value of the voltage across said magnetoresistive sensor;
• output stage, coupled to the input stage, for amplifying and transmitting signals received from the input stage;
• and
• feedback means, coupled from the output stage to the input stage, for correcting variations in said bias voltage levels.