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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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Assuming an i<strong>de</strong>al input transconductor <strong>Gm</strong>3, it is possible to plot an abacus of the<br />

linearity of the filter versus the linearity of <strong>Gm</strong>2, for various <strong>Gm</strong>1 linearity levels. <strong>Gm</strong>1 and<br />

<strong>Gm</strong>2 have been set to a common same value for the plot.<br />

Figure 99. Filter Linearity versus <strong>Gm</strong> linearity<br />

Figure 100. Filter Linearity versus Q-factor<br />

Figure 99 and Figure 100 show that linearity is intrinsically strongly <strong>de</strong>gra<strong>de</strong>d by the<br />

gyrator. For instance, if both transconductors have 20dBm OIP3, filter linearity will reach<br />

10dBm IIP3 for a filter Q-factor of 5. And the higher the Q-factor, the stronger this<br />

<strong>de</strong>gradation.<br />

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