Impedence transformation

[ravet]

Hello

in michael perot lectures, he said:
"Since VCO operates over a very narrow band of
frequencies, we can always do series to parallel
transformations to achieve a parallel network for
analysis"

why??, in rf microelectronics book of razavi, page 51, he discuss impedence transformation, but i didnt realize why narrow band condition????

 

[wenadinho]

because high Q?

 

[bageduke]

Yes, because Q=ω*L/R and only when Q>>1, Ls=Lp. If frequency varies in very large range. High Q would not be true.

 

[qiushidaren]

I think it is because ω*L/R should be a value typically greater than 3 for nonolithic inductors, and this can only be satisfied by a narrow band of frequencies.

Regards,
Cherry