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We experimentally evaluated the effect of crosstalk between crossing microstrip lines (MSLs) on our MSL receiver. The measurement circuit consisted of two crossing MSLs, referred to as the upper MSL and lower MSL. At the crossing area, the upper MSL and lower MSL were separated by a 400-nm thickness of SiO2 thin film. The parasitic capacitance between them was estimated to be about 0.1 pF. We measured bias margin of the receiver connected to the lower MSL under two conditions: with a pulse train running through the upper MSL, i.e., with crosstalk noise, and without a pulse train in the upper MSL, i.e., without crosstalk noise. Our measurements showed that (i) crosstalk mainly reduced the lower limit of the receiver’s bias margin, and (ii) this reduction of bias margin was enhanced by resonance when the repetition frequency of pulses in the upper ring satisfied resonance condition. [Copyright &y& Elsevier]

To expand designable circuit scale, we have developed a new cell-based circuit design for single flux quantum (SFQ) circuit. We call it CONNECT cell library. The CONNECT cell library has over 100 cells at present. Each CONNECT cell consists of a Verilog digital behavior model, circuit information, and a physical layout. All circuit parameter values have been optimized for obtaining the widest margins and minimizing interactions between cells. At the layout level, we have defined a minimum standard cell size and made cell height and width a multiple of the size. Using this cell library, we can easily expand circuit scale without the time-consuming dynamic simulations of whole circuits. For estimation of the reliability of the library, we designed and fabricated test circuits using CONNECT cells. We demonstrated experimentally correct operations, which means the CONNECT cell library is sufficiently reliable. [Copyright &y& Elsevier]

Abstract: We have designed, fabricated and tested a time-to-digital converter (TDC) using SFQ logic circuits. The proposed TDC consists of two sets of ring oscillators and binary counters, and a coincidence detector (CD), which detects the coincidence of the arrival of two SFQ pulses from two ring oscillators. The advantage of the proposed TDC is its simple circuit structure with wide measurement range in addition to the high resolution and the high sensitivity of the SFQ TDC compared to semiconductor TDCs. The time resolution of the proposed TDC is limited by the resolution of the CD. In order to improve the resolution, we have developed a dynamic AND (DAND) gate, which can detect two simultaneous SFQ signal inputs with high accuracy. It was demonstrated that the time resolution of the TDC using the DAND gate is improved to be ±4ps. [Copyright &y& Elsevier]

The performance of high-end routers will soon reach the limits of conventional technology. Single flux quantum (SFQ) digital technology is a key technology for achieving a breakthrough. We have already proposed a high-end router using SFQ technology. In this paper, we report on the latest innovation of SFQ router technology. First we describe a design methodology development. We have developed a new SFQ logic cell library for cell-based top-down circuit design. To expand the circuit scale further, a novel pseudo-automatic Josephson transmission line (JTL) routing technique has also been developed. And then, we discuss issues of passive interconnection, and show the operation of a passive transmission line interconnected circuit up to 40-Gbps throughput. Second we describe a packet switch circuit demonstration. We designed a 2 × 2 crossbar packet switch circuit, which is a key element in the packet switch. We successfully tested the circuit up to a clock frequency of 35 GHz. Finally we discuss an SFQ circuit application in the optical router as an alternative application strategy. [Copyright &y& Elsevier]