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

2. 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

3. 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

4. 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

5. 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
E=0 inside the superconductor!

6. 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.

7. High Temperature Superconductor

8. 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.

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

10. - 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

11. - 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

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

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

14. 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

15. 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

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

17. 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

18. 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

19. Flash ADC

20. 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

21. 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

22. Counting ADC (V/F ADC)

23. 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

25. Counting ADC (Flux-Quantizing ADC)

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

27. Delta ADC

28. 5) Low-Pass Sigma–Delta ADC

29. Second order Sigma–Delta ADC

30. Band-Pass Sigma–Delta ADC

31. 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

32. 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)
3) Josephson Junction Digital Circuits - Challenges and Opportunities Marc J. FELDMAN

33. Thanks for your attention