need help: upconversion mixer and downconversion mixer ?

[wireless man]

Does anybody can tell me what is the difference when designing the upconversion mixer and downconversion mixer? What shoud I pay more attention to when design these two mixers? Thks.

 

[kspalla]

The difference lies between the requirements on the filtering.
Ideally mixer can give both up and down frequencies. up conversion mixer just rejects all frequencies except the LO+IF band and vice versa.