System Level Considerations

Chapter System Level Considerations

Radio Frequency Integrated Circuit Design Second Edition Book
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Radio Frequency Integrated Circuit Design Second Edition Book

  • 48 System Level Architecture and Design Considerationswell at IF), but also removes the need for the extra synthesizer, potentially reducing layout area and power dissipation.3.2  System Level ConsiderationsThe next subsections will discuss some of the most important design considerations when specifying the requirements of all the components in the system. For addi-tional information the reader should consider [1–7].3.2.1  The Noise Figure of Components in Series For components in series, as shown below in Figure 3.7, one can calculate the total output noise No(total) and output noise due to the source No(source) to determine the noise figure.The output signal So is given by: 123oiSS G G G= ××× (3.5)The input noise is: (source)iNkT= (3.6)The total output noise is: (total)(source) 1 2 31(added) 2 32(added) 33(added)oioooNNG G GNG GNGN=+++ (3.7)The output noise due to the source is: (source)(source) 1 2 3oiNNG G G= (3.8)Finally, the noise factor can be determined as: == +++--=++(total)1(added)2(added)3(added)(source)(source) 1(source) 1 2(source) 1 2 323111 2111oooooiiiNNNNFNNGNG GNG G GFFFGG G (3.9)The above formula shows how the presence of gain preceding a stage causes the effective noise figure to be reduced compared to the measured noise figure of Figure 3.7  Noise figure in cascaded circuits with gain and noise added shown in each.