DC-Coupled Ultra Broadband Differential to Single-Ended Active Balun in 130-nm SiGe BiCMOS Technology

The dc-coupled (DCC) broadband operation is a fundamental requirement in many applications, especially in optical communication systems. However, circuits allowing differential to single-ended conversion in a DCC fashion are very rare to be found in the literature. In this letter, a novel differential to single-ended ultrabroadband DCC balun in a 130-nm SiGe BiCMOS technology featuring f(t)/f(max) of 300/500 GHz is presented. A circuit analysis and a performance comparison between the proposed balun and two other configurations which are commonly used to convert a differential signal to a single-ended one is carried out. The design of the mentioned balun is described focusing on the trade-offs between gain, bandwidth (BW) and linearity. Measurement results show how the presented topology can achieve a low-frequency power gain of -7 dB and a 1 dB BW of 80 GHz, along with a total harmonic distortion (THD) of 7%.