How do you deal with harmonic problem?

[chihhao]

In Tx path of GSM system

-> matching_GSM
(dual band)PA ->FEM->antenna connector->matching_a
-> matching_DCS


If you find out the 2nd harmonice is very bad in GSM band,
and you change matching_GSM but it didn't work out.

Can you just change matching circuit in either part to solve this problem ?
Or you have any other idea to solve this problem?
Assume PA cross-band isolation is good.
Thanks

 

[hrkhari]

Is it possible for you to implement a differential architecture to suppress the even order harmonics

Rgds

 

[brmadhukar]

Hi,
Assuming if you have all other components correct the normal problem is overdriving the active device. If the input is small (PA is linear and NF is small) te major cause of harmonics is non linearity of the device. This may be due to PS ripple. Hope this helps.
B R M

 

[vfone]

By definition the GSM PA at full power is in the non-linear region.
The output match topology can help to suppress the harmonics.
The resonant frequency of the output shunt caps can help a lot for suppressing harmonics.
Beware that sometimes even T/R switch can generate harmonics.
Try to evaluate first of all the harmonics only of the PA, to be sure that has reasonable levels.

regards