A 2-V low-power CMOS direct-conversion quadrature modulator with integrated quadrature voltage-controlled oscillator and RF amplifier for GHz RF transmitter applications

Abstract

A compact low-voltage low-power CMOS direct-conversion quadrature modulator with integrated quadrature voltage-controlled oscillator (VCO) and radio frequency (RF) amplifier for wireless transmitter applications is proposed and analyzed. By applying both baseband input signals with quadrature phases and quadrature local oscillator (LO) signals to a set of combiners, the quadrature modulation functions can be implemented. The low-power operation is enabled by the current reuse technique used among quadrature modulator, quadrature VCO, and RF amplifier. Because only two transistors and one resistor are cascoded in the critical path of the proposed quadrature modulator between power supply and ground, the supply voltage can be as low as 1.5 V. The proposed circuit structure is used to design a quadrature modulator chip for 1.9-GHz digital enhanced cordless telecommunications (DECT) transmitter applications. The experimental chip is fabricated by using 0.35-m n-well double-poly-triple-metal (DPTM) CMOS technology. The power dissipation is only 18 mW under 2-V power supply voltage. The on-chip quadrature VCO can provide highly accurate quadrature signals without any phase tuning or trimming. The frequency tuning range of the quadrature VCO is 280 MHz from 1.89 to 2.17 GHz at 2-V supply voltage. Due to small mismatch among quadrature signal paths, the measured image ratio is below 42 dBc under 2-V supply voltage when the desired upper side-band (USB) is set at 2 GHz and 51 dBc under 3-V supply voltage when the desired USB at 1.94 GHz. At 2-V supply voltage, the measured LO leakage is 48 dBc. Moreover, the measured second-order intermodulation and third-order intermodulation are less than 46 dBc.