Active Single-Ended to Differential Converter (Balun) for DC up to 70 GHz in 130 nm SiGe

This work presents an integrated active single-ended to differential converter (balun) for mm-wave applications. The design is based on a differential amplifier chain, which is excited single-endedly. The general lower common-mode rejection at higher frequencies is compensated to improve the performance. The circuit offers a bandwidth from dc to more than 70 GHz with a differential conversion gain of 3.6 dB. The balance in amplitude and phase is better than 0.2 dB and 5°, while the group delay variation stays below 2 ps. The balun is optimized for a high linearity with low signal distortion. The differential output-referred 1-dB compression point occurs around 0.8 dBm at 10 GHz and −0.1 dBm at 60 GHz and the maximum output swing is 900 mV peak-peak. The final chip occupies an area of 0.42 mm2 and is fabricated in a 130 nm SiGe BiCMOS process with a maximum oscillation frequency of 450 GHz. The main application of this circuit is the handling of analog data streams, with symbol rates up to 100 GBd/s, occurring in ultra-wideband communication systems. Here it offers, compared to the state-of-the-art, the best amplitude and phase balance with one of the highest reported bandwidths.