• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.17-20
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• 2002

A complex single flux quantum(SFQ) circuit could be made up of various elementary cells such as JTL(Josephson transmission line), Splitter, XOR, DC/SFQ, SFQ/DC, T flip-flop, ‥‥, etc. In this work, we have designed and simulated a SFQ circuit, which consists of DC/SFQ, JTL and SFQ/DC, based on Nb/AlO$_{x}$Nb Josephson junction technology From the simulation, we could obtain the margins for various circuit parameters. And also we have successfully operated the circuit, which was fabricated with the same design, up to the input signal frequency of about 20 GHz.z.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.113-116
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• 2003

Confluence buffers and single flux quantum (SFQ) switches are essential components in constructing a high speed superconductive Arithmetic Logic Unit (ALU). In this work, we developed a SFQ confluence buffer and an SFQ switch. It is very important to optimize the circuit parameters of a confluence buffer and an SFQ switch to implement them into an ALU. The confluence buffer that we are currently using has a small bias margin of $\pm$11％. By optimizing it with a Josephson circuit simulator, we improved the design of confluence buffer. Our simulation study showed that we improved bias global margin of 10％ more than the existent confluence buffer. In simulations, the minimal bias margin was $\pm$33％. We also designed, fabricated, and tested an SFQ switch operating in a DC mode. The mask layout used to fabricate the SFQ switch was obtained after circuit optimization. The test results of our SFQ switch showed that it operated correctly and had a reasonably wide margin of $\pm$15％.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.109-110
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• 2002

The purpose of a superconductive DC/SFQ circuit is to produce a controlled number of picosecond single flux quantum pulses at the output when a slowly changing DC current is applied to the input. In this work, we have designed and simulated a DC/SFQ circuit based on Nb/Al$O_{x}$/Nb Josephson junction technology. From the simulation, we could obtain the margins for various circuit parameters. And also we have successfully operated a DC/SFQ circuit which was fabricated with the same design. The margin for the input bias current of the circuit was observed to be of $\pm$60%, which was very close to the simulated value.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.140-142
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• 2003

We have designed a SFQ (Single Flux Quantum) D2 Cell and Inverter(NOT) for a superconducting ALU (Arithmetic Logic Unit). To optimize the circuit, we have used Julia, XIC and Lmeter for simulations and layouts. We obtained the circuit margin of larger than $\pm$25%. After layout, we drew chip for fabrication of SFQ D2 Cell and Inverter. We connected D2 Cell and Inverter to jtl, DC/SFQ, SFQ/DC and RS flip-flop for measurement.

• Progress in Superconductivity
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• v.4 no.2
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• pp.127-131
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• 2003

We have designed and measured an SFQ(Single Flux Quantum) OR gate for a superconducting ALU (Arithmetic Logic Unit). To optimize the circuit, we used WRspice, XIC and Lmeter for simulations and layouts. The OR gate was consisted of a Confluence Buffer and a D Flip-Flop. When a pulse enters into the OR gate, the pulse does not propagate to the other input port because of the Confluence Buffer. A role of D Flip-Flip is expelling the data when the clock is entered into D Flip-Flop. For the measurement of the OR gate operation, we attached three DC/SFQs, three SFQ/DCs and one RS Flip -Flop to the OR gate. DC/SFQ circuits were used to generate the data pulses and clock pulses. Input frequency of 10kHz and 1MHzwere used to generate the SFQ pulses from DC/SFQ circuits. Output data from OR gate moved to RS flip -Flop to display the output on the oscilloscope. We obtained bias margins of the D Flip -Flop and the Confluence Buffer from the measurements. The measured bias margins $\pm$38.6% and $\pm$23.2% for D Flip-Flop and Confluence Buffer, respectively The circuit was measured at the liquid helium temperature.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.76-78
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• 2003

We have designed and tested an RSFQ (Rapid Single Flux Quantum) NDRO (Non Destructive Read Out) circuit for the development of a high speed superconducting ALU (Arithmetic Logic Unit). When designing the NDRO circuit, we used Julia, XIC and Lmeter for the circuit simulations and layouts. We obtained the simulation margins of larger than $\pm$25％. For the tests of NDRO operations, we attached the three DC/SFQ circuits and two SFQ/DC circuits to the NDRO circuit. In tests, we used an input frequency of 1 KHz to generate SFQ Pulses from DC/SFQ circuit. We measured the operation bias margin of NDRO to be $\pm$15％. The circuit was measured at the liquid helium temperature.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.35-39
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• 2002

We have simulated and laid out a Single Flux Quantum(SFQ) AND gate for Arithmetic Logic Unit by using XIC, WRspice and Lmeter. SFQ AND gate circuit is a combination of two D Flip-Flop. D Flip-Flop and dc SQUID are the similar shape form the fact that it has the loop inductor and two Josephson junction We obtained perating margins and accomplished layout of the AND gate. We got the margin of $\pm$38%. over. After layout, we drew mask for fabrication of SFQ AND sate. This mask was included AND gate, dcsfq, sfqdc, rs flip-flop and jtl.

• Progress in Superconductivity
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• v.3 no.1
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• pp.17-22
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• 2001

Practical implementation of the SFQ technology in most application requires more than single-chip-level circuit complexity. Multiple chips have to be integrated with a technology that is reliable at cryogenic temperatures and supports an inter-chip data transmission speed of tens of GHz. In this work, we have studied two basic issues in building large RSFQ circuits. The first is the reliable inter-chip SFQ pulse transfer technique using Multi-Chip-Module (MCM) technology. By noting that the energy contained in an SFQ pulse is less than an attojoule, it is not very surprising that the direct transmission of a single SFQ pulse through MCM solder bump connectors can be difficult and an innovative technique is needed. The second is the recycling of the bias currents. Since RSFQ circuits are dc current biased the large RSFQ circuits need serial biasing to reduce the total amount of current input to the circuit.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.117-119
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• 2003

We have designed fabricated, and tested an RSFQ(Rapid Single Flux Quantum) 1-bit ALU (Arithmetic Logic Unit). The 1-bit ALU was composed of a half adder and three SFQ DC switches. Three DC switches were attached to the two output ports of an ALU for the selection of each function from the available functions that were AND, OR, XOR and ADD. And we also attached two DC switches at the input ports of the half adder so that the input data were controlled using the function generators operating at low speed while we tested the circuit at high speed. The test bandwidth was from 1KHz to 5 ㎓. The chip was tested at the liquid helium temperature of 4.2 K.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.141-143
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• 2002

We have simulated and Laid out a Single Flux Quantum(SFQ) AND gate for Arithmetic Logic Unit by using XIC, WRspice and Lmeter. This circuit is a combination of two D Flip-Flop. D Flip- Flop and dc SQUID are the similar shape from the fact that it has the a loop inductor and two Josephson junction. We also obtained operating margins and accomplished layout of the AND gate. We got the margin of $\pm$42% over.