A wideband Delta Sigma digital-RF modulator for high data rate transmitters.pdf

1710 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 42, NO. 8, AUGUST 2007 A Wideband
 Digital-RF Modulator for High Data Rate Transmitters Albert Jerng, Member, IEEE, and Charles G. Sodini, Fellow, IEEE Abstract—A wideband software-defined digital-RF modulator targeting Gb/s data rates is presented. The modulator consists of a 2.625-GS/s digital
 modulator, a 5.25-GHz direct digital-RF converter, and a fourth-order auto-tuned passive LC RF band- pass filter. The architecture removes high dynamic range analog circuits from the baseband signal path, replacing them with high-speed digital circuits to take advantage of digital CMOS scaling. The integration of the digital-RF converter with an RF bandpass reconstruction filter eliminates spurious signals Fig. 1. Conventional and proposed modulator architectures. and noise associated with direct digital-RF conversion. An ef- ficient passgate adder circuit lowers the power consumption of the high-speed digital processing and a quadrature digital-IF approach is employed to reduce LO feedthrough and image distinct radio designs for each set of specifications. A wide- spurs. The digital-RF modulator is software programmable to band, programmable RF modulator with high dynamic range is support variable bandwidths, adaptive modulation schemes, and a key building block for a universal transmitter targeting future multi-channel operation within a frequency band. A prototype high data rate systems. IC built in 0.13- m CMOS demonstrates a data rate of 1.2 Gb/s