Abstract: For controlling a voltage generator (1), a control signal (PBM) is used, with an active part having a variable number of pulses (N) which determines the value of the output voltage of the generator. The output voltage of the generator is used to control the contrast of an LCD screen and the number of pulses in the control signal is adjusted in accordance with the temperature of the LCD screen to compensate for the effect that temperature has upon contrast.

Abstract: Encoding is realized by means of a first low-pass input filter (21), a first modulator (20), a second low-pass filter (19), a second modulator (18) whose modulating signal has a frequency which is pseudo-random modified in the course of time, which signal is pseudo-random chosen between two signals of different frequencies (45, 46) and an output filter (17). According to the invention a first generator providing two signals is constituted by two phase-locked loop oscillators each having a frequency divider (7, 9) in the loop and both being controlled by the same reference signal generator (3, 4) while the reference signal generator itself is constituted by an oscillator of the same type (3, 4) controlled by the field synchronizing signal of the television transmitter, and this signal as well as the reference signal are applied to a first pseudo-random generator (14) for controlling the instants of change of the modulation signal. Decoding is effected similarly in the reverse order.

Abstract: A line scanning circuit supplying a sawtooth current to a deflection coil and producing auxiliary voltages by way of a transformer. The currents through the coil and the windings of the transformer are both switched simultaneously by the same interrupter, but these inductances are separated by diodes and are each associated with an arrangement formed by a diode and a retrace capacitor to supply the current during the line retrace and the beginning of the trace of the scan. The transformer and the coil are fed independently of each other to allow a variation of the scanning amplitude without a change of the E.H.T.