D-Band Active Transmission Line with 33-GHz Bandwidth and 13-dB Gain at f_max/2

This article presents a D-band multisection active transmission line (ATL), where each ATL Section consists of a microstrip TL and a cascode Gm cell that senses the TL output and returns a feedback signal to its input. The employed shunt-to-shunt positive feedback compensates the TL loss, amplifies the signal traveling through the TL, and therefore results in a bandpass positive gain with a center frequency of f0. The ATL Section can achieve broadband return losses (RLs) of better than 15 dB over 200% fractional bandwidth (BW) when it is perfectly matched at its input and output ports at f0 (i.e., S11=S22=0 at f0). The proposed ATL Section is a promising choice to be used as the building block of stagger-tuned amplifiers (STAs) since, unlike the tuned-load stages, it does not introduce a mismatch between the neighboring stages in the chain and hence does not limit the overall RL BW of the STA. Assuming that the TL has a characteristic impedance of Z0, the maximum gain BW (GBW) of each ATL Section is achieved when it is terminated to 1.19Z0 at its input and output ports, leading to S21 of 1.51 dB, 3-dB and RL BW of 300 GHz, and GBW of 357 GHz around f0=150 GHz. Multiple ATL sections should be cascaded to obtain a reasonable gain and noise-figure (NF) performance. It is shown that a multisection ATL features a better BW compared to a cascade of identical tuned amplifiers and STAs. To verify the theoretical derivations, a proof-of-concept 17-stage ATL is designed and implemented in a 130-nm silicon germanium (SiGe) bipolar complementary metal-oxide semiconductor (BiCMOS) technology with fmax of 290 GHz. The prototype circuit features a 13-dB average gain over 136-169-GHz BW and supports amplification up to 0.58max of the technology.