  Superconductor electronics fabrication technology developed at MIT Lincoln
Laboratory enables the development of VLSI digital circuits with millions of
Josephson junctions per square centimeter. However, conventional DC and
multi-phase AC biasing techniques already encounter serious challenges for
scaling circuits above several hundred thousand junctions. In this work, we
propose a novel AC-based biasing scheme for RSFQ-type logic families requiring
DC bias. The major step toward this scheme is a superconducting AC/DC rectifier
which we introduced at ASC 2014. Initially, we proposed to connect the
rectifiers to 'payload cells' via superconducting inductors with large
inductance in order to reduce parasitic effects of flux quantization. Recently,
we discovered that this powering scheme works even better at a much lower value
of the inductance, when it is just sufficient to hold only one or two flux
quanta in the inductive loop between the converter and the payload. In this
case, flux quantization in the loop becomes beneficial because the value of
current fed into the payload is defined by the value of the coupling
inductance. Therefore, our AC/SFQ converter powers the payload cell by a single
flux quantum rather than by DC current. Such mode of operation is extremely
energy efficient because the energy is used only to recover flux quantum
consumed by the cell during the logic operation. We present designs of AC/SFQ
converters comprising an AC/DC rectifier and a current conditioning circuit
which we termed an SFQ filter. We also present test results and demonstrate
AC/SFQ powering a payload circuit using circuits fabricated in a new, 150-nm
node of Lincoln Laboratory fabrication technology using self-shunted
Nb/AlOx-Al/Nb Josephson junctions with 600 $\mu$A/$\mu$$m^2$ critical current
density and 200 nm minimum linewidth of inductors.
