5.4 GHz reconfigurable quadrature amplitude modulator using very high-speed OTAs

A new concept for a quadrature amplitude modulator operating at 5.4 GHz that can be reconfigured between 4 QAM, 16 QAM and higher modulation formats is described in this paper. Vector sum in current domain is employed here to perform the direct digital modulation function. The measured data throughput at 5.4 GHz carrier frequency was 16 Mbit/s. Experimental results show that in the 16 QAM mode, the error vector magnitude (EVM) was 6.20% and the dynamic range was from -52 dBm to -8 dBm. The chip was fabricated in 0.13-μm CMOS technology and its core occupied an area of 0.09 mm² due to its simple architecture. The circuit consumed 20 mA of dc current from a 1.2 V supply including the output buffer.