Abstract: An encoding circuit for a SECAM color television transmission, comprising a frequency-modulatable oscillator for a modulating signal which comprises two line-sequential color difference signals, the circuit also comprising a control loop for making the quiescent frequencies in the generated frequency-modulated signal substantially equal to reference frequencies. For this purpose the control loop comprises a multiplexer, a frequency demodulator and two control paths each having two sample- and -hold circuits. The sequence of the signals conveyed by the multiplexer and the time position of the measuring intervals are chosen such that at least a line scan period is located between the quiescent frequency-measuring interval and the reference frequency-measuring interval.

Abstract: Amplitude modulator circuit for modulating a video signal on a carrier signal. A first control loop which is coupled to the output terminal of the modulator comprises a first sampling circuit which is active during reference signal portions for generating a direct current compensation signal which is added to the video signal. As a result thereof the signal at the modulation input terminal of the modulator obtains a value for which, during the sampling interval, the signal at the output terminals is substantially independent of the signal at the carrier input terminal. A second control loop which comprises a second sampling circuit which is active during reference signal portions, generates a second direct current compensation signal which is added to the signal at the output terminal. This eliminates an effect of a variation in the direct voltage level at the output terminal, while the circuit automatically eliminates substantially the effect of an unbalance in the modulator.

Abstract: A gamma correction circuit for a video signal which is simple to be integrated in a semiconductor body and which has a minimum of adjusting points in a simple adjusting procedure. The signal whose gamma is to be corrected is applied to a linear and to a non-linear amplifier circuit, a pulse having a determined amplitude being added in line blanking periods. The amplifier output signals whose black level is fixed are applied to a signal comparison circuit for the pulse amplitudes and a differential signal is fed back to the input of the non-linear amplifier circuit. The signal whose gamma is to be corrected is formed from the amplifier output signals via a potentiometer.