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

This article presents a
${D}$
-band multisection active transmission line (ATL), where each ATL Section consists of a microstrip TL and a cascode
${G} _{\text {m}}$
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
$f_{{0}}$
. 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
$f_{{0}}$
(i.e.,
$S_{{11}}=S_{{22}}={0}$
at
$f_{{0}}$
). 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
$Z_{{0}}$
, the maximum gain BW (GBW) of each ATL Section is achieved when it is terminated to
${1.19}Z_{{0}}$
at its input and output ports, leading to
$S_{{21}}$
of 1.51 dB, 3-dB and RL BW of 300 GHz, and GBW of 357 GHz around
$f_{{0}}={150}$
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
$f_{\text {max}}$
of 290 GHz. The prototype circuit features a 13-dB average gain over 136–169-GHz BW and supports amplification up to
${0.58}f_{\text {max}}$
of the technology.