An 800 MHz monolithic GaAs HBT serrodyne modulator

Abstract

An 800 MHz monolithic mixed-signal serrodyne modulator IC has been developed in GaAs/AlGaAs HBT HI/sup 2/L process optimized for digital applications. This 3/spl times/2.8 mm, 2000+ transistor chip consists of a 7-bit phase accumulator driving a vector modulator, implemented as of a pair of balanced mixers, 5-bit switched-attenuators, buffer amplifiers, and control circuits. The balanced mixer's LO leakage and 3-1 products are typically 25 dB below the carrier at the nominal operating point, with all other spurs better than -50 dBc. Over a 32 dB control range, the 5-bit switched attenuator typically achieves worst-case amplitude and phase errors of 1.5 dB and 1.5/spl deg/, respectively, from 50 to 250 MHz. This first generation chip consumes 2.5 W of dc power and clocks to speeds in excess of 925 MHz.