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

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

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The frequency tunability is ensured tuning the clock frequency. This may be observed<br />

in Figure 189.<br />

Figure 189. Frequency tuning of the 4-path filter<br />

As far as selectivity is concerned, the bandwidth of the filter is adjusted tuning the RC<br />

constant of the baseband low-pass filter. The higher the RC constant, the smaller the<br />

bandwidth. Figure 190 <strong>de</strong>picts the output signal obtained for various C values between 10 and<br />

100pF.<br />

Figure 190. Selectivity tuning of the 4-path filter<br />

Another important parameter to analyze is the duty cycle of the clock, which is 25% in<br />

the nominal case. Trials have been performed to quantify the effect of a 20% and a 30% duty<br />

cycle clock. Simulation results are plotted in Figure 191.<br />

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