Direct digital-RF amplitude modulator in CMOS 90nm

Abstract

Two different wireless transmitter topologies based on an direct digital-RF amplitude modulator (DAM) are presented: a polar modulator and a direct digital-RF IQ modulator prototype. The DAM consists of 255 basic cells digitally activated by an 8-bit amplitude code to shape a non-constant envelope RF output. The cells are segmentaddressed resulting in a very compact 0.007 mm 2 chip area in CMOS 90nm. In order to reduce the spectral images due to the discrete-time to continuous-time conversion a 2-fold interpolation has been implemented. The DAM reaches a peak output power of 5 dBm at 2.45 GHz with 23% drain efficiency. Both direct digital modulator architectures fulfill WLAN 802.11g linearity constrains at 2.45 GHz.