III. Gm-C Filtering - Epublications - Université de Limoges
III. Gm-C Filtering - Epublications - Université de Limoges
III. Gm-C Filtering - Epublications - Université de Limoges
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Newest silicon tuners generations, like NXP TDA 18272 (Figure 36) and 18273, use<br />
switched capacitors banks which enable a higher, though still partial, on-chip integration of<br />
the RF filtering.<br />
Figure 36. NXP TDA18272 (a) and its RF filtering (b)<br />
I.4.b Opportunities & Limitations of active circuits<br />
Today, silicon tuners like the one shown on Figure 36 are integrated in a can, further<br />
integrated on a TV board. Comparable to the metal enclosure of can tuners, this shielding<br />
protects the TV tuner from electromagnetic perturbations coming from other components or<br />
from the environment itself. In<strong>de</strong>ed, the inductors of RF filters are mounted on a board and<br />
these coils act as antennas which catch electromagnetic signals. Electromagnetic coupling<br />
may <strong>de</strong>gra<strong>de</strong> the performances of the RF selectivity, and so the performances of the tuner.<br />
In the coming years, the technological trend is to mount TV tuners directly on the TV<br />
board, among thousands of other components. Hence, without shielding blocking all<br />
electromagnetic perturbations, the TV tuner has to be as less sensitive as possible to its<br />
environment. This is the first reason of studying the opportunities and the limitations of a<br />
fully-active, inductorless, RF selectivity.<br />
Furthermore, discrete inductors currently used show some other drawbacks like the<br />
spread on their values. Hence, a fully-active solution would lead to a very flexible solution<br />
with no external components and being immune to electromagnetic couplings, leading to a<br />
next generation of TV tuners.<br />
In addition, studying fully-active filters will lead to the study of its technological<br />
aspects. In<strong>de</strong>ed, is CMOS or BiCMOS better to realize such a filter? In case of a CMOS filter,<br />
is there a technological no<strong>de</strong> below which the filter becomes less selective? Moreover, is it<br />
possible to take advantage of the smaller R onC<br />
off product of advanced-no<strong>de</strong> MOS switches?<br />
There are many questions that need to be answered once going about fully-active filtering.<br />
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Si