Abstract: A circuit for increasing the stability of a sawtooth signal in regard to thermal drift comprises a conventional generator whose output is controlled by a loop circuit constituted by a switch controlled in opposition with respect to a switch connected in shunt on an integration capacitor, a low-pass filter having a cut-off frequency determined to select substantially the d.c. component and an operational amplifier network for determining the gain of the loop circuit which consequently produces a voltage corresponding to the mean value of the signal. The direct-current voltages and the passive components are so determined that the mean value of the sawtooth signal preferably corresponds to the reference zero potential.

Abstract: An arrangement which enables a contrast range to be defined for the video signal between two adjustable potential levels and thus an increase in contrast to be obtained when the signal intended for an image display varies within a more restricted range. It comprises inserted in the video chain, a circuit for aligning the video signal to a first potential level and an automatic gain control circuit which receives the output of the aligning circuit and performs a complementary alignment to the second potential level. Each circuit includes a loop which responds with a determined time-constant to the respective peak variations in the signal in the course of at least an image scan period.