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

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

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B.2 RF Filter Linearity Measurements<br />

In the following, it is assumed that the RF filter has a unity gain. If it were not the<br />

case, intercept point values would have to be corrected by the gain of the filter. This chapter<br />

aims at presenting how linearity has been measured in the laboratory [B.2].<br />

B.2.a In-band IIP3 measurement<br />

To measure the in-band input referred third or<strong>de</strong>r intercept point, two closely-spaced<br />

tones are applied within the bandwidth of the filter. As explained, these two tones create<br />

intermodulation products. IIP3 can then be related to the difference between the wanted signal<br />

level and the intermodulation products levels by the following equation:<br />

IMR3<br />

IIP3 = + Pin<br />

_ 2tones<br />

(B.27)<br />

2<br />

where Pin_2tones is the power level of the two applied tones.<br />

Power<br />

IMR3<br />

Figure 202. Measurement of the in-band ΙΙΠ3<br />

- 195 -<br />

Frequency

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