Superconducting Technology Assessment - nitrd
Superconducting Technology Assessment - nitrd
Superconducting Technology Assessment - nitrd
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3.3 CAD TOOLS AND DESIGN METHODOLOGIES<br />
A CAD suite that enables a competent engineer who is not a JJ expert to design working chips is essential to<br />
demonstrate the readiness of RSFQ processor technology described in Section 3.1. Presently available software is<br />
satisfactory only for modest-size circuits of a few thousand JJs, and CAD functions unique to superconductive circuits<br />
are poorly supported.<br />
Today the superconductor industry primarily uses the Cadence environment, augmented by custom tools. Stony<br />
Brook University has developed custom programs, including a device-level circuit simulator and an extractor of<br />
inductance from the physical layout. The University of Rochester has moved superconductive IC design to the<br />
Cadence software environment. However, the custom tools are poorly supported by the commercial vendor, if at<br />
all, and significant investment will be necessary to integrate the superconductive electronics (SCE) tools to arrive at<br />
a maintained CAD suite that will support VLSI-scale circuit design.<br />
CAD capability needs to advance to support an increase in integration scale from a few thousand to millions of JJs:<br />
■ Inductance extraction must be extended to sub-micron wires.<br />
■ Device and noise models must be extended to sub-micron JJs.<br />
■ Transmission line models must be extended to the high frequency regime.<br />
■ VHDL models and methods must be extended to larger integration scale<br />
and more complex architectures.<br />
Status<br />
In the last decade, superconductive RSFQ digital electronics has grown in size and complexity as it has moved from<br />
academic research toward applications development. Initially, only a few experts could successfully design circuits<br />
of significant functionality. Two examples of what has been achieved are the line of HYPRES A/D converters, including<br />
the 6,000 JJ design pictured in Figure 3.3-1 and the Japanese-developed microprocessor shown in Figure 3.3-2.<br />
The technology is now accessible to a wider group of designers, due primarily to the introduction of standard<br />
design methodology and industrial CAD tools.<br />
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