A frequency-agile single-chip QAM modulator with beamforming diversity

Architecture and circuit design techniques for VLSI implementation of a sin gle-chip quadrature amplitude modulation (QAM) modulator with frequency agi lity and antenna beamforming characteristics are presented. In order to ach ieve reliable wireless communication modem function, the single chip all-di gital QAM modulator implements various features, including high data rates with bandwidth efficiency, flexibility, meeting a wide variety of user thro ughput requirements with variable and width and data rates in a multi-user system, and robustness, incorporating diversity and redundancy techniques t o guarantee robust communication for various operating environments. The mo dulator components consist of several digital processing building blocks, i ncluding various finite-impulse-response (FIR) filters, an innovative varia ble interpolation filter, a four-channel frequency translator with quadratu re mixer for antenna beamforming diversity, a quadrature direct digital fre quency synthesizer (QDDFS), a numerically controlled oscillator (NCO), a QA M formatter, a pseudorandom noise (PN) generator, an x/ sin x filter, and a microcontroller interface. An optimized architecture and chip implementati on for the variable modulator is derived and evaluated which will support s ymbol rates from 6 kBaud to 8.75 MBaud continuously and digitally flexible IF frequencies up to 70 MHz with four-channel antenna beamforming function.