need help: upconversion mixer and downconversion mixer ?

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.

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.