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Improved Method for Biasing a Magnetoresistive Element

IP.com Disclosure Number: IPCOM000042221D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Bailey, JA: AUTHOR [+2]

Abstract

The head biasing art usually includes a DC-coupled amplifier as a first-gain stage. To bias the head, a feedback network is employed from the amplifier output through a differential integrator. The integrator feedback produces the desired DC response and causes the effect of the bias to be attenuated at the signal frequencies of interest by rolling off the loop gain. With such a configuration, the loop is difficult to stabilize, the allowable output impedance of the head is severely restricted, and the maximum output voltage of the head is restricted. The embodiment of Fig. 1 illustrates a constant current bias connection that eliminates the need for a gyrator or integrator feedback.

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Improved Method for Biasing a Magnetoresistive Element

The head biasing art usually includes a DC-coupled amplifier as a first-gain stage. To bias the head, a feedback network is employed from the amplifier output through a differential integrator. The integrator feedback produces the desired DC response and causes the effect of the bias to be attenuated at the signal frequencies of interest by rolling off the loop gain. With such a configuration, the loop is difficult to stabilize, the allowable output impedance of the head is severely restricted, and the maximum output voltage of the head is restricted. The embodiment of Fig. 1 illustrates a constant current bias connection that eliminates the need for a gyrator or integrator feedback. The illustrated circuit allows for constant-voltage or constant-current biasing of the head and tolerates a very large variation in head output impedance and allows for a much larger head output voltage. T1 and T2 are matched devices, and REXT1=REXT2 . The op-amp maintains the voltage drop across REXT1 equal to Vref . The collector current of T2 equals the collector current of T1 because T1 and T2 are matched. Then, the current in each head element is approximately Vref/REXT1 . Note that the current is independent of head- element resistance. Fig. 2 shows a constant-voltage bias connection. In Fig. 2, the op-amp is connected with unity feedback and the voltage across the left head element is -Vref . Because IC of T1 equals IC of...