An L-band Direct-Digital QPSK Modulator in CMOS

A new direct-digital quadrature phase shift keying (QPSK) modulator is proposed for portable wireless applications. Its compact yet effective design includes passive phase shifters, active baluns and pass transistors for low-power operation. The integrated circuit (IC) has been implemented in a low-cost 0.18 um complimentary metal-oxide semiconductor (CMOS) process with a 1.8 V supply. Experimental results at 1.7 GHz show solid performance with the data transmission rate and carrier rejection exceeding 20 Mbps and 40 dB respectively.