Frequency resolution for PLL - real requirements?

[Fazor V]

Hi,

does anybody know, what is the real required frequency resolution for synthesizers in current wireless transceivers? I have seen the different systems have different channel bandwidths (even overlapped) which in turn determines the frequency step for down conversion. But, hypothetically, if I have, let's say, a wideband baseband ADC (much wider than e.g., 200 kHz in GSM), do I really have to care about every single step?

Thanks for feedback!

 

[RCinFLA]

First there is adjacient and alternate channel selectivity requirements. Some of this selectivity can be accomplished digitally but dynamic range of frontend requires some analog selectivity.

Frequency synthesizer step size in todays GSM chips is very small. The synthesizer is modulated digitally and there is AFC correction done in the Frac-N sythesizers.

There are many design topologies over the years, most of today's are direct conversion or very low I.F. designs with high integration.

 

[FvM]

The original post seems to target to something like a wideband software based radio or a multiband monitoring receiver. Yes, in this case you don't necessarily need PLL fine tuning.

 

[Fazor V]

Thank you for both replies. Yes, indeed, I am interested in wideband spectrum analyses. In this case, I would say that by having wideband baseband, fine tuning requirements could be alleviated.