A CMOS 10-Mbaud 20-mW PAM/QPSK modulator using a digital-to-analog current-division waveshaping converter

A CMOS modulator for broadband PAM and QPSK data formats is presented. The circuit is based on a poly-phase implementation of a traditional all-digital architecture. A digital-to-analog current-division wave-shaping converter serves as an FIR bandwidth limiting filter. Digital data is applied at the input and an analog waveform is produced at the output, without the need for a standard D/A converter at the back-end, thus reducing power consumption and area. The circuit has been fabricated in a 0.8 um CMOS process (MOSIS HPCMOS26G), occupies an area of 1.2-mm/spl times/1.213-mm, and dissipates 20-mW from a single 5 V supply. The maximum baud rate of the modulator is 10-Mbaud. The 33-tap FIR wave-shaping filter insures out-of-band ripples are suppressed by more than 30-dB. This modulator is applicable to broadband digital communication such as wireless telephony, wireless modems and digital video.