A CMOS direct conversion transmitter with integrated in-band harmonic suppression for IEEE 802.22 cognitive radio applications

A CMOS direct conversion transmitter for IEEE 802.22 cognitive radio applications is presented. In-band harmonic distortions are effectively suppressed across the full TV band by exploiting single-conversion dual-path architecture with integrated harmonic rejecting mixers and RF tunable filters. A fractional-N synthesizer with a single LC VCO and a wideband muti-modulus (2/3/4/6/8/12/16/24) divider block provide multiphase LO signals. Implemented in 0.18 mum CMOS, the transmitter delivers 0-dBm with in-band distortions less than -42 dBc across 54 - 862 MHz band without off-chip filters. Image and LO leakage components are also suppressed below -45 dBc and -36 dBc, respectively, through calibration circuitry. Measured P_1dB and OIP₃ are +9 dBm and +20 dBm, respectively.