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Balanced SAW filters

Hi All, I am designing a RF front end for a single frequency receiver. (My RF knowledge is ok, but limited)

My design utilizes SAW filters as bandpass filters. I have a design that uses two filters, one filter (connected to antenna) is unbalanced and the second filter is after an amplifier and it feeds a log amp, it is balanced.

While I like this design I do not want to order two types of saw filters, balanced and unbalanced. I can find the filter I want in balanced form only.

Can a balanced filter be used as unbalanced? Perhaps a balun? Would this still be suitable at the antenna where the impact of losses would be significant?

Thanks

Rich

Reply to
rich
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The conversion from unbalanced to balanced can be (if you have already conditioned the signal) just a transistor with equal collector and emitter resistors. The conversion from balanced to unbalanced is easier (short or disconnect one wire...).

Reply to
whit3rd

You should be able to make or buy a fairly low loss balun. A more valid question to ask may be "how much does it cost?".

Bandwidth? Cost drivers? Space constraints? Etc.?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

Are you saying that one connection of a balanced filter (one per side) can be left unconnected? Short? To what?

Thanks

Rich

Reply to
rich

Depends on the item in question. If the differential output is a pair of collectors (like in a Gilbert cell) just short the collector resistor (or, if parasitics matter) use the same impedance for the unused collector as the signal path presents. If the differential output is a transformer winding, and the center tap is NOT present and grounded, ground the unused output. If there's a center tap connection, leave the unused output open, of course.

The signal may be smaller, and the noise on bias sources will=20 be more important to consider with a single-ended signal, of course.

Reply to
whit3rd

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