Datapoint Corporation

Charles E Lawrence

Peter H Halpern

Floyd H McDougall

Jay W Lundschen

Improved gain control is obtained in each receiver of a LAN interface or hub in a LAN of the type using amplitude critical signals for conveying information. An evaluation circuit compares a signal representing a calibration value to a predetermined limits and adjusts the gain by one of a plurality of amplification levels to maintain a high level signals which are more accurately decoded into digital information. Improved noise cancellation is also obtained by creating a primary copy and an inverted copy of the received amplitude critical signal, amplifying the primary and inverted copy signals by the same predetermined amount and adding the amplified signals. The addition reinforces the value of the received amplitude critical signal while effectively subtracting the noise effects.

Technique for cancelling common mode switching noise to achieve reduced

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.

Pulse shaping network for disc read circuitry

A peak detecting network utilizes a passive integrating filter to translate the peaks of an input signal into zero crossings of a translation signal, while providing a high degree of noise rejection and preventing the build-up of a DC component in the translation signal. The peak detecting network includes a sine pulse-forming filter comprised of a parallel cascade of a DC shunt inductor, a plurality of series LC sections, and a terminating capacitor. The series LC sections are characterized by respective transfer functions whose impulse responses are substantially finite time duration sine pulses of a successive number of cycles. A rectifier network applies a rectified input signal to the sine pulse-forming filter. A buffer network taps the response of the LC section associated with a one-cycle sine pulse impulse response. The resulting translation signal has a positive-going zero crossing corresponding in time to the occurrence of a peak of the rectified input signal. A positive-going zero crossing detector then detects the sequence of positive-going zero crossings of the translation signal in order to retrieve the sequence of the peaks of the input signal.

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Boerne, TX, United States of America

Charles E Lawrence