| 1. |
- Engseth, Henrik, 1972, et al.
(författare)
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High frequency test bench for Rapid Single Flux Quantum circuits
- 2006
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Ingår i: Superconducting Science and technology. ; 19, s. S376-S380
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Tidskriftsartikel (refereegranskat)abstract
- We have designed and experimentally verified a test bench for high frequency testing of Rapid Single Flux Quantum (RSFQ) circuits. This test bench uses an external tuneable clock signal that is stable in amplitude, phase and frequency. The high frequency external clock reads out the clock pattern stored in a long shift-register. The clock pattern is consequently shifted out at high speed and splitted to feed both the circuit under test and an additional shift register in the test bench for later verification at low speed. This method can be employed for reliable high speed verification of RSFQ circuit operation, with use of only low speed readout electronics. The test bench consists of 158 Josephson junctions and occupied area is 3300 * 660 (mikro meter)^2. It wasexperimentally verified up to 33 GHz with +- 21.7 % margins on the global bias supply current.
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| 2. |
- Engseth, Henrik, 1972, et al.
(författare)
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Room Temperature Interface for RSFQ Digital Signal Processor
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. ; 17:2, s. 979-982
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a cryogenic Multi-Chip Module (MCM) probe for testing of a superconducting hybrid Digital Signal Processor (DSP) capable of 24 giga multiply accumulate operations per second. The probe has 39 data channels with 4 GHz bandwidth, a 30 GHz high speed clock input line, and 48 biasing lines. The MCM interface board features 164 spring finger contacts for a 30 mm x 30 mm MCM. The probe has low heatload (0.23 W) and provides good magnetic shielding with residual field equal to 250 Flux quanta over a 5 mm x 5 mm area. The measured time skew between 20 of the 1200 mm data coaxial lines is about 70 ps. The probe allows synchronous data word transmission at 2 Gbps.
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| 3. |
- Rafique, Raihan, 1978, et al.
(författare)
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Miniaturization of superconducting passive filters for on-chip applications
- 2007
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Ingår i: 11th International Superconducting Electronics Conference, Washington DC, USA, June 10-14, 2007.. ; 11, s. P-V09
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present techniques to miniaturize superconducting ultra narrowband filters for on-chip applications. The filters are designed for 2 GHz, 5 GHz and 10 GHz operating frequencies. The expected bandwidths of the designed filters are 2-20 MHz. The designs are of 7 stages Chebyshev filters having maximum passband ripples of 0.5 dB. On-chip filters are particularly interesting as they are applicable for monolithic design with the RSFQ circuit aiming qubit applications. One of the designs is a quasi-lumped filter where the effective wave propagation constant has been increased by the addition of lumped components to the superconducting microstrip line (SMSL). Additionally, this design provides the optimum width of an SMSL without violating design rules. The other design consists of distributed and lumped components. The area of the filter is in the range of 1-2 square mm. We present the filter topologies and corresponding experimental results for the frequency response of these on-chip filters designed for Hypres 4.5 kA/cm2 fabrication process.
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| 4. |
- Rafique, Raihan, 1978, et al.
(författare)
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Miniaturized superconducting microwave filters
- 2008
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Ingår i: Superconducting Science and technology, press.
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present methods for miniaturization of superconducting filters. We consider two designs of 7th order bandpass Chebyshev filters based on lumped elements and a novel quasi-lumped element resonators. In both designs the area of the filters, with a central frequency of 2-5 GHz, is less than 1.2 mm2. Such small filters can be readily integrated on one board for multi-channel microwave control of superconducting qubits. The filters have been experimentally tested and the results are compared with simulations. The miniaturization resulted in parasitic coupling between resonators and within eachresonator that affected primarily stopband and bandwidth increase. The severity of the error depends on the design in particular, and was less prawn when groundplane was used under the inductances of the resonators. The best performance was reached for the quasi-lumped filter with central frequency of 4.5 GHz, quality factor of 100 and 28 dB stopband.
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| 5. |
- Rafique, Raihan, 1978, et al.
(författare)
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Modeling of superconducting MCM contact for high speed RSFQ circuit
- 2005
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Ingår i: 7th European Conference on Applied Superconductivity, 11-15 September 2005, Vienna, Austria.. ; 7th
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work discusses modeling of Multi-Chip-Module's (MCM) contact for superconducting RSFQ circuits. At MCM contact bumps are formed between chips and carriers' pads to make electrical contacts and the SFQ pulse propagation depends on the impedance matching and contact resistance at bump contacts. Without careful optimization, desired SFQ pulse transmission through the contact bump cannot be achieved. Modeling is an important step towards the design and optimization of MCM contact bump. Studies have been done on the bumps and contact pad structures and an empirical model has been proposed. The p representation of this model has been estimated from the simulated scattering matrix for a wide frequency band, I-V data with proper mathematical model of bump shape. The model contains thefollowing parameters: contact pads' capacitance to ground, bump inductances, contact resistance, mutual inductance between signal and ground bumps and other parasitic corresponding to the layout of the contact pad structure. This model has been used for optimization of the MCM contact structures to achieve return losses of less than -20 dB for more than 210 GHz, the SFQ pulse's bandwidth. The Optimized MCM contact provides SFQ driver, SMSL receiver datalink to work at 30 Gbit/s with 30% perational margin and can work up to 113 Gbit/s of operational speed. Several test chips have been designed with contactbumps for fabrication in Hypres 4.5 kA/cm2 process to verify the simulation results of scattering matrix data and corresponding operational margin.
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| 6. |
- Rafique, Raihan, 1978, et al.
(författare)
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Niobium Tunable Microwave Filter
- 2009
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 57:5, s. 1173-1179
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Tidskriftsartikel (refereegranskat)abstract
- A superconductor bandpass filter with tunable centralfrequency in the range of 2.1–3.5 GHz has been implementedusing Superconducting Quantum Interference Devices (SQUID).The filter is designed as two pi–network resonators connected by a transmission line. Both resonators have a SQUID inductor with a tuning range of 65–200 pH, controlled by DC current magnetically coupled to the SQUIDs. Over a frequency tunability of 40% from 3.5 to 2.1 GHz, the filter has a corresponding fractional bandwidth of 35% to 27% and a mid-band insertion loss of 0.5–3.0 dB. Due to the presence of active elements, the tunability of the filter depends on the power of the microwave signal. A maximum power of -52dBm corresponds to a frequency tuning range of 15%. Spectral measurements by controlling the central frequency of the filter with variable pulse-width shows that the filter can be tuned at a rate of 120 GHz per us.
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| 7. |
- Rafique, Raihan, 1978, et al.
(författare)
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Optimization of high frequency flip-chip interconnects for digital superconducting circuits
- 2006
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Ingår i: Superconductor Science and Technology. - 0953-2048 .- 1361-6668. ; 15:5, s. S354-S361
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results of optimization of Multi-Chip-Module (MCM) contact pads and driver circuitry for gigabit chip-to-chip communication. Optimization has been done using 3D Electromagnetic (EM) simulations of flip-chip contacts and time domain simulations of drivers and receivers. A single optimized flip-chip contact has signal refection of less than -20 dB for up to 503 GHz bandwidth. The MCM data link with optimized SFQ driver, receivers and two MCM contact has operational margins on global bias current of +-30% at 30 Gbit/s speed and can operate at maximum 113 Gbit/s of operational speed. High bandwidth transmission requires realization of an advanced flip-chip process with small dimension of contact pads (less 30 micro meter) and small hight of bumps in the order of 2 micro meter. Current processes with about 7 micro meter hight of the bumps requires application of Double Flux Quantum (DFQ) driver. The data link with DFQ driver was also simulated. It has operational margins on global bias current of +-30% at 30 Gbit/s, however the maximum speed of operation is 61 Gbit/s. Several test structures have been designed for measurements signal re°ection, bit error rate (BER) and operational margins of the data link.
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| 8. |
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| 9. |
- Rafique, Raihan, 1978, et al.
(författare)
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Optimization of Superconducting Microstrip Interconnects for Rapid Single-Flux-Quantum Circuits
- 2005
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 18:8, s. 1065-1072
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the issues related to the optimization ofsuperconducting passive interconnects are discussed. The results of the microwave optimization of bends, vias connections and crossings of the superconducting microstrip lines (SMSL) are reported. The optimum design of the SMSL cross gives more than 95% of transmission and can be well used in two busses cross design with up to 14 signal wires. The results have been confirmed by time-domain simulations and measurements.
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| 10. |
- Rafique, Raihan, 1978, et al.
(författare)
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RSFQ based microwave controller for qubit
- 2007
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Ingår i: 11th International Superconducting Electronics Conference, Washington DC, USA, June 10-14, 2007.. ; 11, s. P-U05
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a Rapid Single Flux Quantum (RSFQ) microwave controller for superconducting qubits. Applying microwaves from room temperature sources is the conventional approach to excite quantum state transitions. Finding a method to apply short microwave bursts with a narrow linewidth is a challenge for on-chip Josephson based oscillators. We present a scheme containing an RSFQ pulse generator, ultra narrowband filter, SQUID based resonator and coupler. The operating frequency of the designed controller is 3-6 GHz. The unique feature of this design is a SQUID based resonator. By varying magnetic field in the SQUID, theresonance length can be varied between λ/4 and λ/2. Theresonator is added as a shunt between the filter and coupler. Transmission of microwave signals from the filter to the output is determined by the shunt resonance. RSFQ T flip-flop circuit is designed to control the magnetic field applied to the SQUID in the resonator. Miniaturization of the coupler of 2-10 GHz has been done using a quasi-lumped element designed. We present the simulations results for the frequency response ofdifferent resonance lengths of the modulator.
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