III. Gm-C Filtering - Epublications - Université de Limoges

I. Introduction to TV tuners and to RF Filtering
I.1 TV Signals Transmission
I.1.a Video Signal Transmissions
I.1.a.i Image Generation
A TV screen consists in several thousands of pixels associated together on a
rectangular panel. Each pixel is made of three photo-emittive cells, each covered by a
different colored filter: a red, a green and a blue one. Using the additive colors principle,
depicted on Figure 1, the screen is able to display a colored picture. This coding of colors may
rely, for instance, on three colors. This is called RGB coding, for Red-Green-Blue.
Figure 1. Additive colors principle
I.1.a.ii Transmission of a TV Signal – Example of Analog Modulation
As it may be seen on Figure 2, to transmit a TV signal, the RGB coding of the picture
is multiplexed with sound, synchronization signals and teletext pieces of information. This
complete TV signal is then modulated, in order to be adapted to the transmission medium, and
emitted through electromagnetic waves or cable.
Figure 2. From picture coding to signal emission
I.1.b Modulation
Modulation is the principle of a signal transmission. As explained in [I.1], modulation
is required in both wired and wireless system. Indeed, coaxial cables shielding is better at high
frequencies whereas for wireless communications, the size of the antenna should be a
significant fraction of the wavelength to realize a sufficient gain. Depending on the nature of
the source signal, i.e. whether it is analog or digital, the modulation is different but it usually
consists in a high-frequency carrier modulated by the useful signal.
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