Direct AC-coupled amplifier with improved common mode rejection for MR heads
First Claim
1. An amplifier for providing a signal from a selected one of a plurality of magnetoresistive read elements comprising, in combination:
- a first differential amplifier having first and second inputs and first and second outputs;
a plurality of input circuits each havingfirst and second connection means for connecting opposite sides of a magnetoresistive element, anda pair of emitter-follower circuits comprising a first transistor having a base connected to the first connection means, a collector arranged to be connected a first voltage source and an emitter, and a second transistor having a base connected to the second connection means, a collector arranged to be connected to the first voltage source and an emitter;
a first capacitor connected between the emitter of each of the first transistors and the first input of the amplifier;
a second capacitor connected between the emitter of each of the second transistors and the second input of the amplifier, the first and second capacitors providing AC coupling and DC blocking between the emitters of each first and second transistor and the amplifier;
a source of bias current; and
means for applying the bias current to the first and second connection means of a selected one of the input circuits.
7 Assignments
0 Petitions
Accused Products
Abstract
A direct AC-coupled amplifier for use with a plurality of magnetoresistive read elements includes a differential amplifier having first and second inputs and first and second outputs. A plurality of input circuits are provided, one for each MR element. Each input circuit has first and second connections to opposite sides of the respective MR element and a pair of emitter-follower its. Each emitter-follower circuit comprises a transistor having a base connected to one of the connections and a collector arranged to be connected a first voltage source. A capacitor is connected between the emitter of each of the transistors and a respective input of the amplifier. A current is applied to the first and second connections of a selected one of the input circuits to operate the respective MR element.
22 Citations
18 Claims
-
1. An amplifier for providing a signal from a selected one of a plurality of magnetoresistive read elements comprising, in combination:
-
a first differential amplifier having first and second inputs and first and second outputs; a plurality of input circuits each having first and second connection means for connecting opposite sides of a magnetoresistive element, and a pair of emitter-follower circuits comprising a first transistor having a base connected to the first connection means, a collector arranged to be connected a first voltage source and an emitter, and a second transistor having a base connected to the second connection means, a collector arranged to be connected to the first voltage source and an emitter; a first capacitor connected between the emitter of each of the first transistors and the first input of the amplifier; a second capacitor connected between the emitter of each of the second transistors and the second input of the amplifier, the first and second capacitors providing AC coupling and DC blocking between the emitters of each first and second transistor and the amplifier; a source of bias current; and means for applying the bias current to the first and second connection means of a selected one of the input circuits. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
-
-
18. An amplifier for providing a signal from a selected one of a plurality of magnetoresistive read elements comprising, in combination:
-
a plurality of input circuits each having first and second terminals for connecting to opposite sides of a magnetoresistive element, first emitter-follower circuit comprising a first transistor having a base connected to the first terminal, a collector arranged to be connected a first voltage source and an emitter, and a first emitter-follower circuit comprising a second transistor having a base connected to the second terminal, a collector arranged to be connected to the first voltage source and an emitter; means for applying a bias current to the first and second terminals of a selected one of the input circuits; a first capacitor having a first side connected to the emitter of each of the first transistors; a second capacitor having a first side connected to the emitter of each of the second transistors; and third and fourth transistors forming a differential amplifier, the third and fourth transistors each having a collector, a base and an emitter, the emitters of the third and fourth transistors being connected together and to a current drain, the collectors of the first and second transistors being coupled to respective first and second outputs of the amplifier, a second side of the first capacitor being coupled to the base of the third transistor and a second side of the second capacitor being coupled to the base of the fourth transistor so that the first and second capacitors providing AC coupling and DC blocking between the input circuits and the differential amplifier.
-
Specification