how to design a RF transceiver ( 900M-2G) ?

Do you plan to use the same front end for both bands?

You can see from many service manuals of mobile phone, if they are dual band design, they use two LNAs for separate receiver part.

What exactly are you trying to do? A broadband transceiver that can cover the whole range?

Cross

For cellular application, you need separate LNA+Mixer for 900Mhz and 2Ghz. After downconvection, the BB AMP, filter and so on could be shared by 900Mhz and 2GHz. Need an extra band selector.

A broadband (continuous) transciever will be almost impossible to do. Multiple band selected transceiver linked by switches is feasible.
The IF section can be shared.

Antenna will be another difficult part.

regards,
mwpro

:D mwpro,
How deal with Antenna ?

The antenna was shared by 900Mhz and 2 GHz at least for dual band cellular phone.