SEPARATE I AND Q BASEBAND PREDISTORTION IN DIRECT CONVERSION TRANSMITTERS

摘要

In-Phase (I) and Quadrature (Q) signals passing from a modem into a direct conversion transmitter are predistorted separately from, and independently of, one another. The I signal is predistorted to compensate for nonlinearities in the baseband I path circuitry between the modem and the upconverter. The Q signal is predistorted to compensate for nonlinearities in the baseband Q path circuitry between the modem and the upconverter. By employing the separate I and Q path baseband predistortion method, 4FMOD power in the upconverted and amplified signal as supplied to the transmitter antenna is reduced or eliminated. In one example, the transmitter employs single sideband modulation in the 777-787 MHz Verizon Band 13 while transmitting 23 dBm in a single LTE RB without emitting more than -57dBm/6.25kHz 4FMOD power into a nearby 763-775 MHz public safety band that starts only two megahertz away from the lower bound of Band 13.