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.