A High-Precision Quadrature Modulator Using a Fully-Differential CMOS Flip-Flop Phase-Shifter Suitable for the Next-Generation RF Transceivers

In recent years, the number of wireless devices that use multi-level quadrature amplitude modulation (QAM) is increased, thereby requiring high-precision quadrature modulators composed of low-cost CMOS circuits. This paper first describes an architecture of a dual-local-oscillator (LO) switching quadrature mixer or modulator, thereby enabling high modulation accuracies. It features the compensation mechanism of phase errors of quadrature (I/Q) LO signals. This technique can be applied to digital modulation/demodulation and sideband or image-signal rejection in frequency conversion processes. Next, we propose a high-precision quadrature modulator, combining the dual-LO switching technique and a newly-proposed fully-differential CMOS flip-flop phase-shifter suitable for modern RF transceivers using multi-level QAM.