Transducer signal amplifier and transducer bias circuits

Claim 2

Apparatus for reproducing magnetically pre-recorded data from a magnetic record medium and comprising a direct current biased electromagnetic transducer means responsive to magnetic variations of the pre-recorded medium to vary the magnitude of the bias current, said apparatus being characterised by an inductive component connected in series in the bias current path and operative, in use, to offer substantially no resistance to flow of steady current while offering an impedance to current variations representing data sufficiently high to divert those current variations to a detector device.

Claim 3

Apparatus as claimed in claim 1, further characterised in that the electromagnetic transducer means comprise two magnetoresistive elements forming a bridge circuit with two inductive components, the junctions between the two elements and between the two components being connected to a pair of D.C. voltage input terminals and the remaining two junctions of the bridge between the elements and the components being connected to the input terminals of a differential detector device.

Claim 4

Apparatus as claimed in claim 1 or 2, further characterised in that the or each inductive component is provided by a gyrator.

Claim 5

Apparatus as claimed in claim 2, further characterised in that the two inductances are provided by two differentially cross-coupled gyrators.

Claim 6

Apparatus as claimed in claim 4, further characterised in that the cross-coupled gyrators comprise a first operational amplifier means connected to a first terminal of the transducer means, a second operational amplifier means connected to a second terminal of the transducer; a shared capacitive means interconnecting the first operational amplifier means and the second operational amplifier means; a first feedback resistor operably associated with the first operational amplifier means; and a second feedback resistor operably associated with the second operational amplifier means whereby each amplifier means, together with its associated feedback resistor and the shared capacitive means simulates an inductive means suitable for biasing said M-R transducer.

Claim 7

Apparatus as claimed in claim 5, further characterised in that the first differential amplifier means includes an amplification stage; a first biasing source operably connected to the amplification stage; active load circuit means operably connected to the amplification stage; an output terminal operably connected to the amplification stage; a first feedback resistor operably connected to the amplification stage; a high impedance means operable to isolate the amplification stage from the output terminal; a second biasing source connected to and operable for biasing the high impedance means; and means for generating a reference voltage source for the first and second biasing source.

Claim 8

7 . Apparatus as claimed in claim 6, further characterised in that the amplification stage includes a pair of emitter coupled transistors.

Claim 9

Apparatus as claimed in claim 6 or 7, further charac- tersied in that the second differential amplifier means includes an amplification stage; active load circuit means connected to the amplification stage; a third biasing means connected to and operable to bias the amplification stage; an output terminal connected to the amplification stage; an isolating means connected so as to isolate the output terminal from the amplification stage; a fourth biasing source connected to the isolating means; and means for generating a reference voltage source for the third and fourth biasing source.

Claim 10

A differential cross-coupled gyrator comprising in combination: a capacitive means with two terminals connected thereto; a first amplification stage connected to one of the terminals; first active load circuit means connected to the amplification stage; a first output terminal; a feedback means interconnecting the amplification stage with said terminal; means for isolating the output terminal from the amplification stage; first biasing means to bias said amplification stage; second biasing means for biasing the isolating means; a second amplification stage connected to the second capacitive plate; second active load circuit means operable for loading the second amplification means; a second output terminal; a second feedback resistor interconnecting the second output terminal to the second amplification stage; second means for isolating the second output from the second amplification stage; third bias means for biasing the amplification means; fourth bias means for biasing the second isolating means; and reference voltage source operably connected to the bias means.

Claim 11

A differential cross-coupled gyrator comprising in combination: a capacitive means with two terminals connected thereto; a first amplification stage connected to one of the terminals; first active load circuit means connected to the amplification stage; a first output terminal; a feedback means interconnecting the amplification stage with said terminal; means for isolating the output terminal from the amplification stage; first biasing means to bias said amplification stage; second biasing means for biasing the isolating means; a second amplification stage connected to the second capacitive plate; second active load circuit means operable for loading the second amplification means; a second output terminal; a second feedback resistor interconnecting the second output terminal to the second amplification stage; second means for isolating the second output from the second amplification stage; third bias means for biasing the amplification means; fourth bias means for biasing the second isolating means; and reference voltage source operably connected to the bias means.

Claim 12

A differential gyrator for use with an M-R transducer comprising in combination: a capacitor; a first and a second amplification stage positioned symmetrically with the capacitor; a first and a second bias means operable for biasing the first and second amplification stage; a pair of output terminals one of each connected to the first and second amplification stages; a pair of feedback resistive means interconnecting the output terminal of each stage with the associated amplification stage; a pair of isolating means operable to isolate each stage from the output terminal; first means for biasing the amplification stages; second means for biasing the isolating means; and a reference source operably connected to the biasing means.

Claim 13

A differential gyrator for use with an M-R transducer comprising in combination: a capacitor; a first and a second amplification stage positioned symmetrically with the capacitor; a first and a second bias means operable for biasing the first and second amplification stage; a pair of output terminals one of each connected to the first and second amplification stages; a pair of feedback resistive means interconnecting the output terminal of each stage with the associated amplification stage; a pair of isolating means operable to isolate each stage from the output terminal; first means for biasing the amplification stages; second means for biasing the isolating means; and a reference source operably connected to the biasing means.