Low-noise preamplifier for magneto-resistive heads.

摘要

A d.c. current source (17) provides current through a field effect transistor (12) and the effective resistance (18) of a magneto-resistive element to ground. A feedback loop including an operational transconductance amplifier (26) provides a bias voltage for the field-effect transistor (12) whereby the voltage across said effective resistance (18) of said magneto-resistive element is held constant while the resistance of said element changes. The resulting a.c. current flowing through the magneto-resistive element flows only through the feedback loop and an output resistor (25) connected across the inputs (22 and 24) of the operational transconductance amplifier (26). The amplification of the circuit is approximately the resistance of the output resistor divided by the resistance of the magneto-resistive element. <IMAGE>