Noise in thin-film inductive heads

The sources of thermal noise in thin-film inductive recording heads are investigated. These noise sources are associated with the various losses in the heads. An equivalent circuit model of the head impedance whose parameters are fitted to the measured impedance over a 100-MHz frequency range has been made. The head is read out by a low-noise preamplifier whose input impedance and input-referred voltage and current noise are also measured. Of the ensuing channel front-end (head plus preamplifier), the total noise is determined as well as the relative contributions of the various head and electronics noise sources and their spectral distribution. For a typical (36 turns, 5.6 μm trackwidth) head and a 20-MHz channel bandwidth, most of the noise was contributed by the DC-resistance of the copper coil (R_c =21.6 Ω). The voltage and current noise of the electronics came next. For higher data rate channels the current noise of the electronics and the eddy current damped magnetization rotation over the skin depth in the center region of the yoke were shown to be the important noise sources