CMOS highly linear direct-conversion transmitter for WCDMA with fine gain accuracy

A highly linear, high output power, 0.13 μm CMOS direct conversion transmitter for wideband code division multiple access (WCDMA) is described. The transmitter delivers 6.8 dBm output power with 38 mA current consumption. With careful design on the resistor bank in the IQ-modulator, the gain step accuracy is within 0.1 dB, hence the image rejection ratio can be kept below -47 dBc for the entire output range. The adjacent channel leakage ratio and the LO leakage at 6.8 dBm output power are -44 dBc - 5 MHz and -37 dBc, respectively, and the corresponding EVM is 3.6%. The overall gain can be programmed in 6 dB steps in a 66-dB range.