Below are the minimum set of requirements we would like from a customer to specify a SAW Duplexer.
Centre Frequencies
If the application is for a tranceiver front end filter, then this is set by the application. The individual filters will be designated transmit (Tx) and receive (Rx).
Passband
There are two passbands, usually the same width. See the SAW filter application note for details.
Input Power Level
The filter designated as the transmit path will usually have a higher power rating than the receive path filter. That means that a duplexer designed for a handset may not be suitable for a base station as the Tx and Rx frequencies will be swapped.
Insertion Loss
The receive filter will be optimised for low loss so may have a lower insertion loss than the transmit filter. This is the loss through the filter within the passband measured at the point of minimum loss.
Package Type
There are many different packages for SAW Duplexers. Lower frequency types require bigger packages because the size of the active area of the filter is proportional to acoustic wavelength in the passband. Much smaller packages for the higher frequency parts are available where space is at a premium.
Operating Temperature Range
This is taken from the temperature range of the equipment the part is designed into with a little extra at the hot end to allow for local heating on the PCB.
See Also
Please also check the SAW filter application note.
Optional Specifications
The above will give us the basics to select a suitable Crystal Filter for an application where there is design flexibility.
Termination Impedance
For SAWs this is often 50Ω. Where this is not the case, external matching components will be required. It is common for the Antenna port to need a shunt inductor to optimise the match.
Storage Temperature Range
This is as the name suggests.
See Also
Please also check the SAW filter application note.