An improved low-power CMOS direct-conversion transmitter for GHz wireless communication applications

The proposed transmitter chip is fabricated in a standard 0.25 μm single-poly-five-metal CMOS process with low resistance substrate. It consists of a quadrature modulator, a quadrature VCO, and a power amplifier. This transmitter IC consumes only 45 mA from a 2.5 V power supply voltage. With highly linear quadrature modulator and low phase-error quadrature VCO structure, the measured LO leakage, image rejection, second-order inter-modulation and third-order inter-modulation of the modulated signal, at the output of transmitter, achieves -59d Bc, -57 dBc, -600 dBc, and -56 dBc, respectively. The three-stage power amplifier is also integrated to provide a 9.8 dBm output power with 15% efficiency for short-range wireless communication applications.