1. Field of the Invention
The invention pertains to an apparatus for the reception of video signals.
It is known that television signals are transmitted in the form of successive lines with the following, notably, for each line: a synchronization pulse, a constant level that acts as a reference for the black level of the image and is called the "back porch", and the video signal in analog form.
In television receivers or, more generally, in video signals reception equipment, there is provision for automatic gain control circuits that make it possible to hold the amplitude of the video signals between limits that are acceptable for good quality of the image. This automatic gain control is usually done by detecting a determined level of the video signal, notably the peak value of the signal, and the signal thus detected is used to activate a gain control device or a variable gain amplifier in order to hold the video signal between the prescribed limits.
2. Description of the Prior Art
It has been observed that the known circuits do not always satisfactorily regulate the amplitude of the video signal, especially when this video signal has to be converted into digital form. Indeed, in this latter case, the problem of the dynamic range of the analog video signal is particularly acute because the analog/digital converter has to be held between a lower level and an upper level, failing which the values that overstep the limits are not restored accurately.
The invention enables a satisfactory regulation of the amplitude of the video signal, notably when there is provision for an analog/digital converter.