A DC--20-GHz InP HBT Balanced Analog Multiplier for High-Data-Rate Direct-Digital Modulation and Fiber-Optic Receiver Applications

This paper reports on a dc-20-GHz InP heterojunction bipolar transistor (HBT) active mixer, which obtains the highest gain-bandwidth product (GBP) thus far reported for a direct-coupled analog mixer integrated circuit (IC). The InP HBT active mixer is based on the Gilbert transconductance multiplier cell and integrates RF, local oscillator, and IF amplifiers. High-speed 70-GHz [f.sub.T] and 160-GHz [f.sub.max] InP HBT devices along with microwave matching accounts for its record performance. Operated as a down-converter mixer, the monolithic microwave integrated circuit achieves an RF bandwidth (BW) from dc-20 GHz with 15.3-dB gain and benchmarks a factor of two improvement in GBP over state-of-the-art analog mixer IC's [1]-[9]. Operated as an up-converter, direct-digital modulation of a 2.4-Gb/s [2.sup.31] - 1 pseudorandom bit sequence (PRBS) onto a 20-GHz carrier frequency resulted in a carrier rejection of a 28 dB, clock suppression of 45 dBc, and less than a 50-ps demodulated eye phase jitter. The analog multiplier was also operated as a variable gain amplifier, which obtained 20-dB gain with a BW from dc-18 GHz, an third-order intercept of 12 dBm, and over 25 dB of dynamic range. A single-ended peak-to-peak output voltage of 600 mV was obtained with a [+ or -] 35-mV 15 Gb/s [2.sup.5] - 1 PRBS input demonstrating feasibility for OC-192 fiber-telecommunication data rates. The InP-based analog multiplier IC is an attractive building block for several wide-band communications such as those employed in satellites, local multipoint distribution systems, high-speed local area networks, and fiber-optic links. Index Terms--Fiber optics, InP HBT, limiter, mixer, multiplier, VGA.