Patent ID: 6331921
Filing Date: 2001-12-18
Classification: G11B,H03F

Abstract:
A head read amplifier circuit of a magnetic read/write system, the head read amplifier circuit comprising:a magneto resistor having a first terminal and a second terminal, the magneto resistor sensing changes in magnetic flux on a surface of a magnetic storage medium and producing changes in the resistance of the magneto resistor in response to the changes in magnetic flux;a bias-current source for generating a bias current for the magneto resistor, the bias-current source having an output terminal coupled to the first terminal of the magneto resistor for passing the bias current through the magneto resistor;a differential feedback circuit coupled to first and second output terminals of the head read amplifier circuit, the differential feedback circuit receiving a differential output voltage generated at the output terminals of the head read amplifier circuit and nulling the differential output voltage, the output of the differential feedback circuit being coupled to the first terminal of the magneto resistor;a common mode feedback circuit, the common mode feedback circuit setting a minimum bias current for the magneto resistor, the common mode feedback circuit being coupled to the second terminal of the magneto resistor via a current-source transistor, the common mode feedback circuit comprising a first cascode circuit and a second cascode circuit, the first and second cascode circuits each comprising a plurality of transistors connected in series, the first cascode circuit having a first terminal coupled to the first output terminal of the head read amplifier circuit and a second terminal coupled to the first terminal of the magneto resistor, the second cascode circuit having a first terminal coupled to the second output terminal of the head read amplifier circuit and a second terminal coupled to the second terminal of the magneto resistor; anda current drain comprising the current-source transistor and an inductor, the current-source transistor having a first terminal, the common mode feedback circuit being coupled to the first terminal of the current-source transistor, the current-source transistor having a second terminal coupled to the second terminal of the magneto resistor, the current-source transistor having a third terminal coupled to a first terminal of the inductor, the inductor having a second terminal coupled to ground, wherein the impedance of the inductor reduces any noise generated by the current-source transistor.