A balanced transmitter up-converts I and Q baseband signals directly from baseband-to-RF. The up-conversion process is sufficiently linear that no IF processing is required, even in communications applications that have stringent requirements on spectral growth. In operation, the balanced modulator sub-harmonically...http://www.google.com/patents/US8036304?utm_source=gb-gplus-sharePatent US8036304 - Apparatus and method of differential IQ frequency up-conversion
