Collector Series-Resistor to Stabilize a Broadband 400 GHz Common-Base Amplifier

The indium phosphide (InP) 130 nm double-heterojunction bipolar transistor (DHBT) offers milliwatts of output power and high signal amplification in the lower end of the terahertz frequency band when the transistor is used in a common-base configuration. Instrumentation can directly benefit from this technology by enabling the development of novel broadband sources or synthesizers that rely on our ability to amplify the signal over enormous bandwidths. However, the design of high gain and stable amplifiers presents many obstacles and limitations as we increase the bandwidth and the carrier frequency. Here, we show that adding a series resistor at the collector terminal of the common-base transistor prevents instabilities in the terahertz monolithic integrated circuit amplifier and increases its fractional bandwidth. Adopting this technique, we report a state-of-the-art broadband common-base amplifier that exhibits a minimum small-signal gain of 18.9 dB from 325 to 477 GHz. This amplifier presents the highest fractional bandwidth and gain above 300 GHz. Our work demonstrates the feasibility of high-performance amplifiers that address the need of future terahertz electronic systems.