Global interconnects in VLSI complexity single flux quantum systems (original) (raw)

Rapid single-flux quantum (RSFQ) is one of the most advanced superconductive electronics technologies. SFQ systems achieve operate at tens of gigahertz with up to three orders of magnitude smaller power as compared to CMOS. In conventional SFQ systems, most gates require clock signal. Each gate should have the fanins with equal logic depth, necessitating insertion of path-balancing (PB) DFFs, incurring prohibitive area penalty. Multiphase clocking is the effective method for reducing the path-balancing overhead at the cost of reduced throughput. However, existing tools are not directly applicable for technology mapping of multiphase systems. To overcome this limitation, in this work, we propose a technology mapping tool for multiphase systems. Our contribution is threefold. First, we formulate a phase assignment as a Constraint Programming with Satisfiability (CP-SAT) problem, to determine the phase of each element within the network. Second, we formulate the path balancing problem as a CP-SAT to optimize the number of DFFs within an asynchronous datapath. Finally, we integrate these methods into a technology mapping flow to convert a logic network into a multiphase SFQ circuit. In our case studies, by using seven phases, the size of the circuit (expressed as the number of Josephson junctions) is reduced, on average, by 59.94 % as compared to the dual (fastslow) clocking method, while outperforming the state-of-the-art single-phase SFQ mapping tools.

Rapid Single Flux Quantum (RSFQ) logic is well-known for its ultra-high switching speed and extremely low power consumption. In this paper, we present two original experiments to demonstrate that it's also a reliable technology and its reliability is sufficient even for such a large-scale system as a proposed petaflops-scale HTMT computer. We have measured the bit error rate (BER) for a circular register of inverters representing a critical path of a 64-bit integer adder, and timing jitter in a 200 Josephson junction (JJ) long transmission line, imitating a branch of a clock distribution tree, both being important and representative building blocks of the HTMT computer. For the adder critical path we have demonstrated the highest clock frequency of 17 GHz, latency of 860 ps and BER of 10-19 for 3.5 μm technology of HYPRES, Inc. The value of timing jitter was 200 fs per JJ for 1.5 μm technology of TRW, Inc. These figures are in good agreement with our simulations

During the physical design process, the second process of the quantum circuit design flow, using some optimization techniques after layout generation might be useful to improve the metrics or meet the design constraints. Focusing on this issue, this paper proposes an optimization technique using gate location changing to improve the latency of quantum circuits. The proposed technique uses layout and scheduling information to find critical paths and improve their latency by changing locations of the gates on the critical paths. Experimental results show that the proposed technique decreases the latency of quantum circuits up to 26% for the attempted benchmarks.

In order to achieve speedup over conventional classical computing for finding solution of computationally hard problems, quantum computing was introduced. Quantum algorithms can be simulated in a pseudo quantum environment, but implementation involves realization of quantum circuits through physical synthesis of quantum gates. This requires decomposition of complex quantum gates into a cascade of simple one-qubit and two-qubit gates. The methodological framework for physical synthesis imposes a constraint regarding placement of operands (qubits) and operators. If physical qubits can be placed on a grid, where each node of the grid represents a qubit, then quantum gates can only be operated on adjacent qubits, otherwise SWAP gates must be inserted to convert nonlinear nearest neighbour architecture to linear nearest neighbour architecture. Insertion of SWAP gates should be made optimal to reduce cumulative cost of physical implementation. A schedule layout generation is required for ...