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

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

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Developing previous expression:<br />

Figure 25. LO time evolution<br />

Figure 26. LO frequency spectrum<br />

( ( ± ω ) ) + cos(<br />

( ω ± 3ω<br />

) t)<br />

+ cos(<br />

( ω ± 5ω<br />

) t)<br />

...<br />

cos ω +<br />

(I.8)<br />

RF<br />

LO t RF LO<br />

RF LO<br />

As said, the IF frequency is <strong>de</strong>fined as:<br />

ω = ω − ω<br />

(I.9)<br />

IF<br />

RF<br />

Now, the RF signal is not only ma<strong>de</strong> of the wanted channel, but it is also composed of<br />

other RF unwanted signals that may be located so that following relations are verified:<br />

IF<br />

RF 3 −<br />

RF 3 −<br />

LO<br />

ωIF = ω 3ω<br />

LO<br />

(I.10)<br />

ω = ω 5ω<br />

(I.11)<br />

LO<br />

- 24 -

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