An InGaP-HBT IC chipset for 40-Gbps optical-transmission systems was developed on the basis of a microwave-circuit design scheme design techniques, circuit configurations, and concepts. A distributed amplifier achieved greater than or equal to50-GHz bandwidth and greater than or equal to164-GHz gain-bandwidth product, which are state-of-the-art values for GaAs-HBT-based baseband distributed amplifiers. A compact 40-GHz analog phase shifter with small insertion-loss variation, and 20-GHz/40-GHz clock amplifiers with very low power consumption (about 10 mW) were also realized. Moreover, a new approach-inserting impedance-transformer circuits-to enable 'impedance matching' in high-speed digital ICs was successfully applied to a 40-Gbps decision circuit to prevent unwanted gain peaking and jitter Increase caused by transmission lines without sacrificing chip size.