Pulse shaping network for disc read circuitry

Abstract

A pulse shaping network for the read circuitry of a floppy disc memory system in which encoded digital data is recorded in a double density format. The pulse shaping network processes an uncompensated input read signal in order to substantially eliminate cross talk between the bivalent pulses of the read signal, thereby correcting the peak phase shift and peak amplitude distortion that characterizes intersymbol cross talk. The resulting phase and amplitude corrected read signal can then be accurately decoded in order to retrieve the information contained in the peak phases of the read signal. The pulse shaping network includes a sine pulse-forming filter comprised of a capacitively terminated parallel cascade of series LC sections characterized by respective half-period harmonic transfer functions whose impulse responses are substantially finite time duration sine pulses of a successively odd multiple of half cycles. The input read signal pulses are applied to the sine pulse-forming filter, and a buffer circuit is used to separately tap the responses of the first two LC sections. These responses, which correspond to the convolution of the read signal pulses with the first and third half-period harmonic transfer functions of the filter, are then scaled and applied to a difference amplifier that provides the corrected read signal output of the pulse shaping network. An equalization analysis of the read signal pulses yields the optimum harmonic content, including scaling factors, for the combined network transfer function of the filter so as to substantially eliminate intersymbol cross talk by effectively narrowing in time the pulses of the input read signal. Since the network transfer function is formed of only lower order harmonics, the response of the pulse shaping network is band width-limited so that the signal-to-noise ratio is not seriously degraded.