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AN1993 Datasheet(PDF) 4 Page - NXP Semiconductors |
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AN1993 Datasheet(HTML) 4 Page - NXP Semiconductors |
4 / 23 page AN1993 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved. Application note Rev. 3 — 13 August 2014 4 of 23 NXP Semiconductors AN1993 High sensitivity applications of low-power RF/IF integrated circuits If the single conversion architecture of Figure 1 were implemented with a 455 kHz IF, any interfering image would be received almost as well as the desired frequency. For this reason, dual conversion, as shown in Figure 3, has been popular. In the application of Figure 3, the first IF must be high enough to permit the pre-selector to reject the images of the first mixer and must have a narrow enough bandwidth that the second mixer images and the intermod products due to the first mixer can be attenuated. There is more to it than that, but those are the basics. The multiple conversion heterodyne works well, but — as Figure 3 suggests — compared to Figure 2 it is more complicated. Why then, don’t we use the approach of Figure 2? a. Attenuation of low-side image with 10.7 MHz b. Attenuation of low-side 455 kHz image Fig 2. Effects of pre-selection on images ∆ pre-selector freq. (MHz) −40 40 10 −10 002aah474 −30 −10 10 −60 −20 0 20 −40 −20 0 desired frequency pre-selector filter LO image 10.7 MHz IF ∆ pre-selector freq. (MHz) −40 40 10 −10 002aah475 −30 −10 10 −60 −20 0 20 −40 −20 0 desired frequency pre-selector filter LO image 455 kHz IF Fig 3. Dual conversion 002aah476 first mixer first LO pre-select filter first IF filter IF amp demod audio and/or data second mixer second LO second IF filter |
Similar Part No. - AN1993_15 |
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