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Method to Detect an Open Magnetoresistive Element

IP.com Disclosure Number: IPCOM000042561D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Marbach, KD: AUTHOR

Abstract

Magnetic recording equipment is moving in the direction of using magnetoresistive elements as read heads. As the equipment has become more sophisticated, the need has arisen for the equipment to do self-checks of itself for any problems. This article details a method through which an open magnetoresistive element (also called an MR head) can be detected. This method for detecting an open MR element is based on monitoring a bias circuit, as shown in Fig. 1. This circuit forces the voltage across the head to equal the reference which is applied to the inverting input of the operational amplifier (op amp). The op amp provides the bias transistors with a base voltage which causes a current to flow in them. This current flows through the MR head, causing a voltage drop across it.

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Method to Detect an Open Magnetoresistive Element

Magnetic recording equipment is moving in the direction of using magnetoresistive elements as read heads. As the equipment has become more sophisticated, the need has arisen for the equipment to do self-checks of itself for any problems. This article details a method through which an open magnetoresistive element (also called an MR head) can be detected. This method for detecting an open MR element is based on monitoring a bias circuit, as shown in Fig. 1. This circuit forces the voltage across the head to equal the reference which is applied to the inverting input of the operational amplifier (op amp). The op amp provides the bias transistors with a base voltage which causes a current to flow in them. This current flows through the MR head, causing a voltage drop across it. The feedback resistors R1 and R2 construct a common mode voltage across the MR element and feed it back to the op amp to correct any deviations from the reference. Fig. 2 shows the voltage ranges of the output of the op amp for both open and normal MR elements. This graph shows a definite gap between the voltage ranges for open (either one or both sides) and normal heads. This gap can be used as an advantage in detecting an open MR element. A voltage reference can be set up in the gap between the voltage ranges for open heads and normal heads. This voltage reference is connected to a comparator along with the output of the op amp used to bias the magnetoresistive element, as shown in Fig. 1. The comparator then gives one voltage level when the MR head is operating normally and another level when it is open. This circuit could be implemented in several ways to also include checking multiple tracks. Fig. 3 shows the implementation chosen for biasing and checking tw...