Patent EP-0154086-A2 (EP)
Inventor: VINDING JORGEN PLESNER
IPC: H04B3/06
Filed: 1984-11-29
Abstract: @ A data recovery circuit for a data recording/transmission system wherein information is encoded in an equalised data signal comprising at least partly doublet pulses, each valid doublet pulse comprising two adjacent opposite polarity pulses, the data recovery circuit being arranged to distinguish individual doublets from noise in the equalised data signal, receiving the equalised data signal, and responsive thereto supplying a doublet indentification signal identifying individual portions of the equalised data signal as constituting doublets, comprises a differentiator (11) connected to receive the equalised data signal to provide an output signal having a waveform following the time derivative of the equalised data signal, and having a predetermined delay time. A first comparator (15, 16) is connected to receive an output of the differentiator (11) for providing, as an output, a logic level signal having first, second and third instantaneous states indicating that the output signal of the differentiator is respectively less than, within, or greater than a first predetermined signal range whose minimum corresponds to an equalised data signal slope smaller than a first predetermined negative slope, and whose maximum corresponds to a slope greater than a second predetermined positive slope. An amplifier (20) is connected to receive a delayed equalised data signal for supplying an amplified output signal having a waveform following the equalised data signal and delayed by a predetermined delay time therefrom. A delay element is connected to receive the equalised data signal, for supplying the delayed equalised data signal to the amplifier (20). An analog gate (23, 24) is connected to receive the amplified output signal from the amplifier and the logic level signal from the first comparator (15) for supplying an output signal including a first portion following the amplified output signal while the logic level of the first comparator means has exclusively its first state and a second portion following the amplified output signal while the logic level signal of the first comparator has exclusively its third state, each portion having a predetermined level otherwise. A second comparator (27) is connected to receive the output of signal of the analog gate (23, 24) for producing responsive thereto, a logic signal having first, second and third instantaneous states, the first state and the third state of the second comparator indicating, respectively, that the first portion and the second portion of the output signal of the analog gate are outside a second predetermined signal range, and the second state of the second comparator indicating that, both first and second portions of the output signal of the analog gate are within the second predetermined range, the second predetermined signal range substantially corresponding to the minimum excursion of the equalised data signal between points (i) having slopes corresponding to the first and second predetermined slopes and (ii) between peaks of a valid doublet pulse, the second comparator producing a doublet identification signal.