GB939055A - A process for the production of polymeric materials - Google Patents

Abstract

939,055. Automatic phase control systems; transistor circuits. AMPEX CORPORATION. Sept. 4, 1962 [Sept. 12, 1961], No. 33914/62. Drawings to Specification. Classes 40 (5) and 40 (6). In reproducing recorded colour television signals the subcarrier burst is gated out from the reproduced composite signal and used to generate pulses at positive-going zero cross-over points of the subcarrier cycles which then sample the instantaneous amplitude of sawtooth waves derived from a stable reference oscillator of frequency equal to the sub-carrier frequency, to produce a D.C. control voltage which acts on an electronically variable delay line in the path of the reproduced signals, for the duration of one line, to compensate and correct any phase errors. Further, a coarse D.C. phase control voltage may be added to the above fine control voltage, derived by comparing reproduced horizontal or other sync pulses with a reference pulse train of equal or related frequency. The cross over detector (i.e. pulse generator) may comprise a normally conductive transistor cut off by positive going half cycles of subcarrier burst (after limiting), to produce ringing in a resonant collector circuit limited to half a cycle by a shunt rectifier, thereby producing pulses with timing determined by the phase of the subcarrier. A similar cross-over circuit may be used for the sawtooth generator, pulses produced as above from a crystal oscillator charging through a transistor amplifier a capacitor whose discharge through a transistor emitter follower produces the sawtooth with subcarrier recurrence frequency. Feedback from the emitter output circuit to the capacitor discharge resistance produces a linearising bootstrap effect. The subcarrier frequency pulses and saw tooth are then respectively applied across and to the centre tap of a transformer secondary connected across the bases of a PNP and NPN pair of transistors, with emitters feeding a capacitor deriving the D.C. control voltage. The subcarrier burst is gated out by a delayed reproduced horizontal sync pulse whose trailing edge triggers a transistor blocking oscillator to provide a pulse, of burst width, transformer coupled to a diode ring bridge to open it and pass only the subcarrier burst from an applied composite reproduced television signal. The diode bridge is normally non-conductive due to being shunted by a circuit having normally conductive rectifiers but rendered non-conductive by the blocking oscillator pulses. A delay and gate circuit (Fig. 5, not shown) may act on the subcarrier frequency output pulses from the cross-over detector circuit so that the start and finish of the burst is dispensed with. In this delay circuit an emitter follower is energized by the blocking oscillator output pulses and a selected duration of the pulses is derived by a transistor amplifier having a tuned circuit; an input R-C circuit of the amplifier and the tuned circuit both producing a delayed output. Spikes and transients may be removed from negative going reproduced horizontal sync pulses by applying them to block a normally conducting series rectifier so that an R-C circuit discharges and after 2 Ásec. delay opens a normally blocked transistor until the negative sync pulses ceases, i.e. pulses of less than 2 Ásec. duration are eliminated but the timing of the rear edge of the transmitted sync pulse is unchanged.