GB1068024A - Improvements in or relating to discrete-level pulse transmission systems - Google Patents

Abstract

1,068,024. Transistor pulse-shaping circuits; pulse modulation; data transmission systems. PLESSEY-UK Ltd. Feb. 19, 1964 [Feb. 21, 1963], No. 6945/63. Headings H3T, H4L and H4P. In a digital single-sideband pulse transmission system of the kind employing pulses having two or more discrete levels, and durations equal to integral multiples of a basic bit duration and in which the reference or zero level in received pulse trains is subject to variation due to distortion, in the transmission path, of the low-frequency components, so that pulses regenerated from the received signal are liable to be subject to error, a low-frequency component is derived from the regenerated pulse output, by a network which distorts the signal waveform by the same amount but in the opposite sense to the distortion inherent in the transmission system, the low-frequency component derived at the output of the network being combined with the received pulse train to compensate for said variation in zero level. It is stated that a single-sideband system of transmission involves the use of filter networks at the transmitter which introduce distortion of the low-frequency sidebands, and also permit transmission of a certain amount of unwanted sideband whereby further distortion is introduced during detection at the receiver. Thus a pulse signal I, Fig. 2, may appear at the input of a pulse regenerator, Fig. 1, at the receiver, as shown at II. The signal II is combined in adding network 1 with a signal III derived from the regenerated output to reproduce a signal IV from which the wander in the zero level has been eliminated. This is shaped and limited in amplitude quantizer 2, which delivers a signal VI to time quantizer 4 and digit rate extractor 3. The latter circuit comprises a square-wave generator which is synchronized by the signal VI applied thereto and from which are derived sampling pulses VIII for application to circuit 4. The sampling pulses cause circuit 4 to derive from the input signal IV applied thereto an output signal V which is an accurate replica of the original signal waveform I except for the introduction of a half-bit delay. The output from network 4, comprising the overall regenerated output signal, is applied to a low-frequency network 5 which, Fig. 3 (not shown), comprises a plurality of cascaded emitter-follower stages spaced by resistance-capacity networks so designed that it delivers an output III which compensates for the low-frequency distortion introduced during transmission.