Voltage measurement circuit for a magnetoresistive head installed in a

Abstract

A circuit forming part of an arm electronics module installed on an actuator arm that measures the voltage across an MR head A control unit supplies a measurement enable signal that enables a measurement enable circuit. A current bias circuit, responsive to the control unit, supplies a bias current to the MR head. A common node in the circuit provides a voltage signal responsive to the voltage across the MR head, with an added diode V.sub.BE drop across an input transistor. A voltage measurement amplifier has an input node and an output node that supplies an output voltage reduced in voltage by one diode drop (V.sub.BE). An input switch, responsive to the measurement enable signal is coupled between the input node and the common node. An output switch, responsive to the measurement enable signal is coupled between the output node and an output terminal. The output terminal is connected to a connector pin in an electrical connector via a flex cable to provide a convenient point for test and calibration apparatus to sample the MR head voltage. The circuit advantageously allows the MR head's voltage to be measured during assembly of and after merging into a disk enclosure, providing essential information for optimizing each MR head's operating point. Furthermore, an electrical short circuit may be provided across the MR head during the manufacturing process to prevent damage to the MR head due to electro-static discharge (ESD). The short can be left in place until merging into the disk enclosure and then, after merging, the voltage measurement circuit can be utilized to measure the voltage of the head with the short removed. Furthermore, the voltage measurement circuit can be enabled some time after normal operation of the disk drive begins, for purposes such as reoptimizing the bias currents through the MR heads or for failure analysis.