[SOLVED] Why does SAW filter has only 10 dBm maximum input level ??

[F45566]

Hi,

In general, for passive components, we don't have to care their linearity.
Because their linearity is extremely high.
At least, their linearity MUST be higher than active components.


Nevertheless,

The following is an active component, SPDT switch, its P1dB = 18 dBm

Excellent overload capability (1 dB gain compression point +18 dBm at 300 MHz)

**broken link removed**


The following is a passive component, SAW Filter, its P1dB = 10 dBm

Maximum ratings Source power PS 10 dBm

**broken link removed**




I'm confused, why does a passive SAW filter have worse linearity than am active SPDT switch ????
And it has only 10 dBm P1dB ?????
Due to the SAW filter's poor linearity, I can NOT put it in PA output.

Would anyone please tell me what documents should I study to understand its detailed meaning ?
Or what keywords should I google ??


Thanks a lot~!

 

[tony_lth]

SAW filter is designed for RX, not for TX.
SOrry I don't know the IC art, but it must has some drawback for high power SAW.
If you need high performance filter after PA, cavity filter is always used.

 

[G4BCH]

A SAW filter is a Piezo-electric device, it works by mechanically stressing the substrate to launch the acoustic waves.
There is a limit to which the subtrate can be stressed and still remain linear.
If the drive is too high the transducers wiil tear themselves from the substrate, they are only a few microns thick.

 

[mtwieg]

Passive doesn't necessarily mean linear. Diodes, for example. All susceptible materials have some limit to polarization. See here.

 

[jiripolivka]

A typical SAW filter has an insertion loss of 18 dB. So one cannot use such filter in a RF PA. SAW filters are used in receivers (like TV) where it is possible to use a post-amplifier to replace the loss.
Where the linearity is a problem, do not use SAW but another filter.

 

[biff44]

also, you can blow up the saw. There are just some fingers of tiny metallization that cause the saw to mechanically vibrate. If you put in too much power, those fingers can vaporize.