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Design >> RF Design >> Placement of the SAW filter
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Message started by vp1953 on Aug 17^th, 2010, 4:58pm

Title: Placement of the SAW filter
Post by vp1953 on Aug 17^th, 2010, 4:58pm

Hi All,

Typically for ASK/FSK transceiver chips, we find that the saw filter is placed at the receiver; the other end of the SAW filter goes to the R/T switch which is connected to the antenna.

Is there any issue that prevents the SAW filter from being placed between the R/T switch and the antenna (instead of at the receiver)?

Title: Re: Placement of the SAW filter
Post by pancho_hideboo on Aug 18^th, 2010, 10:25am

vp1953 wrote on Aug 17^th, 2010, 4:58pm:

Is there any issue that prevents the SAW filter from being placed between the R/T switch and the antenna (instead of at the receiver)?

Load stability of TX-PA.

Consider impedance of SAW especially for stop band.

Title: Re: Placement of the SAW filter
Post by vp1953 on Aug 18^th, 2010, 12:00pm

Hi P_H,

Thanks for the excellent suggestion. Is there any way this can be simulated?

Title: Re: Placement of the SAW filter
Post by rfcooltools.com on Aug 18^th, 2010, 3:45pm

Adding to pancho_hideboo's comments
The saw will not see any loss between it and the antenna therefore the return loss will vary by two times the insertion loss of the switch. You could say that the impedance seen looking into the antenna from the saw filter will vary more.

Also
Tx path will now have a saw as loss so output power will be reduced by the saw insertion loss

The benefits is that fcc spurious transmission requirements will be easier to be met.

do you have an s2p file of the saw filter and switch if so check out my simulator where you can load them in and quickly try some what if scenarios for matching return loss etc.

http://rfcooltools.com

Title: Re: Placement of the SAW filter
Post by vp1953 on Aug 19^th, 2010, 10:35am

Hi RFcooltools,

Thanks very much for your input. I will definitely play around with your simulation tool - looks pretty interesting!

Title: Re: Placement of the SAW filter
Post by rfcooltools.com on Aug 20^th, 2010, 10:07am

Thanks vp1953,

Feel free to let me know what you think good or bad!

http://rfcooltools.com