Low power low noise amplifier for a magnetoresistive sensor

An amplifier for amplifying differential input signals comprising a first and a second input signal, the amplifier comprising:

• a first and a second first-polarity transistor each having an input terminal responsive to the first input signal;
• a first and a second second-polarity transistor each having an input terminal responsive to the second input signal;
• at a first node, a first terminal of the first first-polarity transistor connected to a first terminal of the first second-polarity transistor;
• at a second node, a first terminal of the second first-polarity transistor connected to a first terminal of the second second-polarity transistor;
• a first current source supplying a first DC bias current at a second terminal of the first and the second first-polarity transistors;
• and
• a second current source supplying a second DC bias current at a second terminal of the first and the second second-polarity transistors, wherein the first bias current is different from the second bias current.

A preamplifier for receiving differential input signals, comprising a first and a second input signal, from a magnetoresistive element, the preamplifier comprising:

• a first and a second PMOSFET each having a gate responsive to the first input signal;
• a first and a second NMOSFET each having a gate responsive to the second input signal;
• at a first node, a first source/drain of the first PMOSFET connected to a first source/drain of the first NMOSFET;
• at a second node, a first source/drain of the second PMOSFET connected to a first source/drain of the second NMOSFET;
• a first current source supplying a first DC bias current to a second source/drain of the first and the second PMOSFETS;
• a second current source supplying a second DC bias current to a second source/drain of the first and the second NMOSFETS, wherein the first current is different from the second current;
• and
• a first and a second load element connected between a power supply and the first and the second nodes, respectively.

A method for amplifying differential input signals comprising a first and a second input signal, the method comprising:

• supplying a first DC bias current;
• supplying a second DC bias current wherein the first DC bias current is different from the second DC bias current;
• amplifying the first input signal to produce a first output signal;
• amplifying the second input signal to produce a second output signal;
• producing a first load current having an AC component responsive to the first output signal and a DC component responsive to the first and the second DC bias currents;
• and
• producing a second load current having an AC component responsive to the second output signal and a DC component responsive to the first and the second DC bias currents.