Patent GB-1486479-A (GB)
Title: Pcm regenerators
IPC: H04L25/52
Filed: 1975-01-03
Abstract: 1486479 Data transmission; pulse regenerators SIEMENS AG 3 Jan 1975 [19 Feb 1974] 225/75 Heading H4P A regenerator comprises an input transformer EU, preferably centre tapped, feeding an amplitude decision device AE and time decision device ZE in series followed by a pulse amplifier PV and shaper PF constituted by a transformer having low pass characteristics which converts input pulses into sinusoidal half waves. Output from the amplitude decision device also feeds a phase discriminator PD which through a filter TPF controls the frequency output of a sinusoidal timing pulse generator TG which is converted into square waves in RF which are fed back to the phase discriminator and time decision device ZE. The phase discriminator has separate channels for positive and negative input signals. The arrangement described receives bipolar pulses and can accept input signals, e.g. sin<SP>2</SP> half wave signals at high bit rates. Amplitude decision device AE comprises transistor pairs T1-T4 forming differential amplifiers with operating point set by resistors R1, R2 with input and output collectors separately paralleled, the latter forming polarized outputs A, B to time decision device ZE comprising two D flip-flops FA, FB with NAND gates GA, GB having timing pulses provided through inverters N1, N2. In accordance with timing signals gates GA, GB emit negative going pulses F, G of half bit width to pulse amplifier PV having a common emitter transistor configuration with the outputs being taken from the collector circuits through a transformer having stray capacitance between windings and additional capacitors form a low pass filter matched to the surge impedance of a cable following. Signals A, B are also led to a phase discriminator comprising flip-flops FDA, FDB with outputs parallel through diodes D1, D2 to one input of a current generator J i.e. the base of transistor T6. The second input is connected to one of a pair of differentially connected transistors T7, T8 through Zener diode Z2 to paralleled collectors of T1, T3. Collectors of T6, T8 are paralleled and provide an output to CR low pass filter TPF forming the input of a crystal timing pulse generator TG providing an output through differential amplifier T10, T11 in which oscillation amplitude is limited and output is "squared" then passed back through inverters N1, N2 to gates GA, GB, flip-flops FA, FB, FDA, FDB. Each phase discriminator output pulse (K) is directly dependent on the phase of the timing signal and is transformed into a current pulse of constant amplitude at J and as a result of signals (C) emitted at the same time which have been transformed into pulses of amplitude (J) and constant width (t1) by Zener diode Z2 and transistors T7, T8, a signal M appears at the output which conducted via low pass filter TPF to timing pulse generator TG which changes the voltage across a capacitance diode and hence the oscillating frequency of the generator. The splitting of the signal path into separate channels for positive and negative pulses reduces the operating frequency of each hence provides the possibility of processing very high bit rates. The crystal pulse generator may be replaced by an LC oscillator; this will result in increased jitter of phase and timing signal resulting in a sharp jump out of the stable part of the phase discriminator curve (Fig. 5, not shown) with incorrect phase hence switch back diodes D3, D4 will be unnecessary. These diodes prevent passage of consecutive bits of equal polarity by blocking D inputs of flip-flops FA, FB. The arrangement is stated to be suitable for I.C. techniques.