Low phase noise, image rejected direct-conversion transmitter in 0.18 μm CMOS

A direct-conversion transmitter is developed at 6 GHz in 0.18 μm CMOS. In order to realize high efficiency quadrature generation as well as bring low deterioration to the overall phase noise, the bulk-coupled technique is adopted into a Class-C type VCO. The image rejection mixer adopts a three-stage poly-phase filter and a pair of Gilbert double-balanced mixer with current bleeding for conversion gain concern. Three-stage two-way combined power amplifier is designed with the purpose to transfer the up-converted differential signal to single-ended one. Based on the measurement, the proposed QVCO achieves a minimum phase noise of -124 dBc/Hz at 1 MHz offset. 2-8 dB improvement is realized compared to the reported works at the frequency of interest. It also realizes 22.6% wide tuning range, resulting a FOM_T value of -201. The transmitter demonstrates a peak value of 40 dBc image rejection ratio, with 24 dBm OIP3 verified under two tone measurement.