US Patent 7542519 Radio frequency transmitter and method therefor

An RF transmitter (10) is configured to transmit either wideband multichannel modulations or narrowband multichannel modulations in a variety of licensed frequency bands (70) using a single set of hardware. For narrowband modulations, a digital IF upconversion stage is performed so that, after upconversion to RF, image signals 74 are sufficiently displaced from the licensed frequency band (70) so as to be filtered off. For wideband modulations, no IF modulation stage occurs, and a direct upconversion takes place from baseband to RF. LO leakage is cancelled using a negative feedback loop that combines a digital DC signal with a communication signal (26, 52) prior to a direct or final analog upconversion stage (62).