Flexible Superconducting Passive Interconnects with 50-Gb/s Signal Transmissions in Single-Flux-Quantum Circuits

Abstract

We have developed a very flexible wiring technique of passive transmission lines (PTLs) in single-flux-quantum (SFQ) circuits. For high flexibility, we introduced two types of wiring structures of strip lines (SLs) and microstrip lines (MSLs) using the fabrication process which has four metal layers. The SLs and MSLs are realized using the second and fourth metal layers as signal lines, respectively, from the bottom (the other two metal layers are used as ground planes). We also introduced via-holes for transmission between the SL and MSL. For solving the problem of impedance mismatch on complicated discontinuous sections such as joints [between the driver(receiver) and the end of SLs(MSLs)] and via-holes, we optimized the structures of these discontinuous sections and evaluated propagation properties to ensure high-speed transmission of SFQ pulses. We tested the transmission of SFQ pulses through SLs/MSLs including more than 50 via-holes, one of the most complicated lines in actual designs. We confirmed the good propagation properties of SFQ pulses up to 50 Gb/s with sufficiently wide bias margins of ±20% to be used in practical designs.

Study on Single Flux Quantum Floating-Point Divider Based on Goldschmidt's Algorithm

“…To evaluate the performance and the circuit scale of the SFQ divider, we designed the bit-serial divider using the cell library we developed [19] for the AIST 10 kA/cm 2 Nb advanced process 2 [20]. In order to reduce the propagation delay of the data, passive transmission lines with the characteristics of 3.5 Ω are used for wiring between each circuit component [21], [22]. Because implementation of the large-scale SFQ lookup table using the current superconducting circuit fabrication process is difficult, use of the SFQ/CMOS hybrid lookup table [23] is assumed in the circuit design.…”

Design of fast digit-serial adders using SFQ logic circuits

“…1, there are lots of interconnections between carry-operator blocks, whose length is not equal. In the design of the interconnection, we introduced passive-transmission line (PTL), which has more flexibility and less propagation delay than Josephson-transmission line (JTL) [8]. To reduce the skews, we carefully designed clock and data paths, so that every path has almost the same length.…”

Proposal of a Desk-Side Supercomputer with Reconfigurable Data-Paths Using Rapid Single-Flux-Quantum Circuits

“…By the passive transmission line (PTL) technology developed recently, in an RSFQ chip, ballistic transmission of an SFQ pulse on superconducting wirings is possible, and therefore, fast and high-throughput intra-chip signal transmission is achieved [7], [8]. Note that RSFQ circuits are free from a delay for recharge process of capacitors/inductors, in contrast to CMOS circuits.…”

“…1 µm process technology with five interconnection layers is now available [6]. The increase of the wiring layers combined with the passive transmission line technology [7], [8] further increases the circuit integration density. Now, it is attractive to make study on computing systems using RSFQ circuits which are difficult to be implemented by using semiconductor circuits.…”