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LNA and filters - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2010 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

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 Post subject: LNA and filters
Posted: Mon Oct 12, 2009 12:41 am 

Joined: Wed Oct 07, 2009 6:27 am

Posts: 6

In the receiver chain which should come first? LNA or BPF. In most of the schematics, I see BPF coming first. I have a wide band LNA. Can i use it at the beginning of the filter chain(because I need high sensitivity)? What will be the problems in this?

 Post subject: Re: LNA and filters
Posted: Mon Oct 12, 2009 4:29 am 

Joined: Sun Oct 04, 2009 5:17 pm

Posts: 6

Hi veerasamy,

The BPF is usually placed before the LNA stage to protect it from out-of-band interference. In this case the total noise figure is increased by a quantity equal to the insertion loss of the filter itself.

Strong out-of-band interferer can generate high intermodulation products depending from the IP3 of your LNA. Very strong interferer can also cause distortion, if they are close or higher than P1dB.



 Post subject: Re: LNA and filters
Posted: Thu Jan 14, 2010 3:01 am 

Joined: Thu Jan 14, 2010 2:57 am

Posts: 4

Hi veera,

Mostly you will not be using a bpf if your antenna is narrowband and you use

an impedance matching circuit. But the rejection of unwanted signals is always

important consideration before an LNA for good performance otherwise more

power will appear @ input of lna which will affect its linearity!!!

 Post subject: Re: LNA and filters
Posted: Tue Jul 13, 2010 9:36 am 

Joined: Tue Jul 13, 2010 8:57 am

Posts: 1


we want to design a receiver in 2.4Ghz with advanced design system software,& we don't know how to find the moduls of LNA & mixer & band pass filter & LPF & amplifier & oscillator &...

help us please..

 Post subject: Re: LNA and filters
Posted: Tue Jul 13, 2010 3:13 pm 

Joined: Thu Jan 14, 2010 2:57 am

Posts: 4

I have used models of various components while designing the wideband frontend for SDR.

I remember that the Avago technologies provides the model for their LNA.

Johansons dielectric also provides models for their passives.

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