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

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

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Figure 136. Filter in-band IIP3 versus central frequency<br />

This latter graph represents the input-referred IP3 of the <strong>Gm</strong>-C filter in two cases:<br />

using i<strong>de</strong>al capacitors associated to i<strong>de</strong>al resistors mo<strong>de</strong>ling the switch Ron, or using the<br />

previously discussed capacitors banks, implemented by means of MOS capacitances. It may<br />

be observed that around 2dB are lost when implementing the capacitors banks.<br />

It is worth adding that at low frequencies the quality factor of the filter using i<strong>de</strong>al<br />

capacitances, and so its gain, <strong>de</strong>creases. The implemented filter has been optimized, through<br />

the size of the switches, to obtain a constant Q-factor. Hence, this explains the linearity<br />

difference at 40MHz.<br />

Table 13 summarizes the performances un<strong>de</strong>r process and mismatch variations. For<br />

these simulations, an i<strong>de</strong>al voltage source for the PDA has been consi<strong>de</strong>red. Very few<br />

variations on these parameters are observed.<br />

Table 13. Process and Mismatch Variations<br />

Mean value Sigma Units<br />

Central frequency 134.1 2.1 MHz<br />

Bandwidth 36.4 0.7 MHz<br />

Q-factor 3.7 0.1 -<br />

Gain 6 0.35 dB<br />

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