Superconductor Analog-to-Digital Converters by : Mahdi Sadjadieh Part 3 Superconductor Analog-to-Digital Converters by : Mahdi Sadjadieh

superconductor circuits enable fast and accurate data conversion between the analog and digital domains Ultra fast switching speed low power natural quantization of magnetic flux quantum accuracy

Commercialization of superconductor microelectronics technology promise to be a key enable of ‘pure’ software radio architectures This chapter provides a description of the underlying technology and its potential in both commercial and defense wireless systems

Josephson junctions exhibit switching speeds of the order of a few picoseconds or less Superconductor ADCs are based on some of the special properties of superconductivity and Josephson junctions and circuits

Zero Resistivity E=0 inside the superconductor! 1908- liquefied helium First discovered in mercury by Kamerlingh-Onnes in 1911. Critical temperature 4.21K. Nobel Prize in 1913. E=0 inside the superconductor!

Meissner Effect B=0 inside the superconductor Superconductor is not just perfect conductor! Supercurrent flowing around the surface to shield the B field. Supercurrent is a superfluid.

High Temperature Superconductor

Josephson Junction Josephson Effect: In superconducting state of certain metals, electrons are attracted by each other and form bound pairs, called Cooper pairs. When these pairs of electrons tunnel through a thin insulating barrier placed between two superconductors, the whole is called Josephson junction.

Josephson Junction Characteristics Control currents Ic, Josephson threshold Im. Gate current Ig, I-V Curve Threshold Curve

- In order to create digital circuits, an active superconductor component is needed : the Josephson junction (JJ) * I < Ic : device exhibits no resistance * I > Ic : JJ becomes briefly resistive

- Design consideration for Josephson junctions in RSFQ circuits is that they be sufficiently damped to prevent hysteresis upon exceeding the critical current, so that the junction quickly return to the Zero voltage - Rapid voltage pulse corresponds to a single flux quantum

Josephson Tunnel Junction Current Insulator (~1 nm) q Magnetic field Damping Parameter IC bc > 1 IC bc < 1 SFQ Technology

What is a SQUID? A SQUID is a Superconducting Quantum Interference Device Construction SQUID is an inductive loop with one or more Josephson junctions

Circuit Characteristics In RSFQ circuits, it in not a static voltage level, but the presence or absence of quantized magnetic flux (fluxons) that represents information bits The basic RSFQ structure is a superconducting ring that contains one Josephson junction plus a resistive shunt outside it

Emerging Applications – Software Defined Radio - in communications, dispersion-free, ultra-high Q superconductor microwave filters are used in cellular base stations - the use of superconductor material allows the very high Qs to be maintained, while microminiaturizing the overall filter size - the ultra-sharp filter 'skirts' that result enable increased channel selectivity and, with a cooled LNA, yield increased sensitivity as well - an increasingly embraced solution to surmount these obstacles and lies in the concepts of software radio - realization of software radio systems presents a host of challenges - chief among them the unprecedented requirement on analog-to-digital converter (ADC) performance - this is the area where superconductor microelectronics represents an emerging solution - with demonstrated ADC, DAC, and DSP components, this technology may well become a key enabling technology for software radio

(table)  summarizes the performance already achieved with such superconducting devices to date - military radio requirements are far more demanding than those for commercial systems

Superconductor Nyquist ADC: Flash ADC the number of required comparators is , one for each quantization level. In contrast, a superconductor flash ADC, based on SQUID comparators, provides a unique solution for drastic reductionof circuit complexity, and at the same time, allows fastersampling

part of ADC The current is a periodic function Vs the applied input current When a clock signal is applied to the sampler, one of these two sampling junctions switches to the resistive state. For a clockwise current ILoop , J2 switches making the output a logical “1,” whereas a counterclockwise current ILoop causes J1 to switch producing a “0” output

Flash ADC

Superconductor Oversampling ADCs 1) Counting ADC (V/F ADC) 2) Counting ADC (Flux-Quantizing ADC) 3) PMD ADC 4) Delta ADC 5) Low-Pass Sigma–Delta ADC 6) Band-Pass Sigma–Delta ADC

Counting ADC (V/F ADC) the firstJosephson ADCs were based on the voltage-to-frequency(V/F) conversion Acts as a voltage-controlled oscillator (VCO) The signal sampling process is performed by counting the number of generated SFQ pulses over a time interval low-passfirst-order sigma–delta modulation

Counting ADC (V/F ADC)

The pulse counting process is done using toggle flip-flops forming a ripple counter, which are the fastest elements in RSFQ technology In order to avoid strong nonlinearities of such a VCO at low input signal, it is necessary to operate the VCO at some input offset. This offset also helps to accommodate positive and negative signals

Counting ADC (Flux-Quantizing ADC)

PMD ADC In order to solve the problem of the quantizer hysteresis, a dc voltage-biased single-junction SQUID quantizer was introduced

Delta ADC

5) Low-Pass Sigma–Delta ADC

Second order Sigma–Delta ADC

Band-Pass Sigma–Delta ADC

Superconducting DigitizerFor Radio Astronomy Hypres, Inc. Elmsford, NY JPL 93 Phase II INNOVATION Produced a superconducting analog to digital converter for radio astronomy applications ACCOMPLISHMENTS Demonstrated a 10 GHz 2-bit digitizer for radio astronomy  Technology provides high sensitivity analog to digital conversion, at very low levels of power consumption  High efficiency allows placement behind sensor array in cryogenic environment COMMERCIALIZATION  Received a $1.5 million contract with the Navy to develop technology for a very sensitive, high performance radar Picture 40 Meter Radio Telescope at Owens Valley Radio Observatory Near Bishop, CA GOVERNMENT/ SCIENCE APPLICATIONS  Radio astronomy and space deployed telescopes operating in the x-ray and ultraviolet range of the spectrum EuroPKI 2005

Refrences 1)Superconductor Analog-to-Digital converters OLEG A. MUKHANOV, SENIOR MEMBER, IEEE, DEEPNARAYAN GUPTA, SENIOR MEMBER, IEEE, ALAN M. KADIN, AND VASILI K. SEMENOV 2)http://en.wikipedia.org/wiki/Superconductivity 3) Josephson Junction Digital Circuits - Challenges and Opportunities Marc J. FELDMAN

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