Extending the bandwidth of magnetic tunnel junction sensors by a buffer amplifier

Abstract

A simple buffer amplifier, consisting of a transistor in an emitter-follower configuration, is proposed to extend the bandwidth of magnetic tunnel junction read sensors. To maximize the bandwidth improvement, the buffer should be used on the slider or on the suspension as near to the slider as possible. The channel front-end (sensor, buffer, interconnect, and preamp) bandwidth is still somewhat limited by the RC product of the sensor resistance and shunt capacitance. However, the buffer can reduce the shunt capacitance to subpicofarad levels, allowing for bandwidths near 1 GHz. Merging the buffer with an interconnect and preamp gives a low-frequency signal-to-noise ratio (SNR) reduction at the preamp input of 0.1 dB and an SNR improvement of 5 to 10 dB over a no-buffer configuration for frequencies between 100 MHz and 1 GHz.