Hi,
Both options are correct, it helps to filter out of band interferers and helps to avoid out of bands spurs generated by the transceiver.
Hope it helps,

Hi,
Could you post the reference?, I suppose that if care it's taken the spurs will be below the emission limits. For the receiver part I can only think right now on two situations were you don't put a band select filter for out of band blockers: UWB systems that cover several GHz of bandwidth and don't make sense to use a filter(although I suppose that the could use something), this systems are usually limited by interferences not noise. The other systems I can think it's the "new" approach to Software Defined RadioReceivers(this transceiver with direct sampling) that are made with the intention of multistandard capability so Bandpass filtering it's not needed(in fact they arise from the need to reduce front ends and filtering), but for what I know they need high linearity front-ends.

Hi didac,

sorry about the delay. The paper is "A Fully Integrated SOC for 802.11b in 0.18-μm CMOS" IEEE Journal of Solid-State Circuits, vol. 40, no. 12, Dec 2005. There are 22 authors, but the first is Shahla Khorram.

Its a good read and it appears to be designed by Broadcom since all the authors work there...

cheers,
Aaron

Hi,
I didn't find a reference design for Broadcom modules(although a couple for other companies and they use the band select filter), but re-reading the paper it appears(I think) the clue for avoiding a band select filter in the input, they indicate that they use two RSSI one before the channel select filter that it's used to estimate the blocker level and adjust LNA gain dynamically so it seems that they can survive to blockers, the other RSSI it's just the typical one.

Hi,
In principle it's true that antenna has a selectivity but in WLAN it's better to expect that the user made some strange things and be sure that the module itself is compliant... Look the attached WLAN antenna(that works and it's very easy to mount) or google for pringles,can antenna.