High Speed Data Measurer for use with Quantum Cryptography and Laser Range Detector

1. High Speed Data Measurer for use with Quantum Cryptography and Laser Range Detector By Michael Noone KanKan Yu Charles Ruiz

2. Outline • Introduction • Objective • Applications • Technology • Cost Analysis • Conclusion • Q & A

3. Introduction • High Speed Data Measurer used as a component for a Laser Range Finder and Quantum Random Number Generator. • Combination of high speed circuit design, optics, and control logic to produce a Laser Range Finder.

4. Applications • High Speed Data Measurer • Laser Range Finder • Quantum Random Number Generator • Laser Range Finder • Computer Imaging Systems • Single use distance detector • Random Number Generator • For use with Quantum Cryptography

5. Objectives • Design and build a high speed timing circuit • Must find the time between rising edges of pulses • Accurate to approximately 50ps • Interface timing circuit to computer • Write control software to interpret data from timing circuit • Design and build laser range finder using timing circuit • Use time of flight range finding technique • Use high speed laser driver • Use high speed receiver • Receiver should filter out all wavelengths except for that of the laser used • Design and build a scanning mechanism that rotates the laser rangefinder skill in one or two axes

6. Technology

7. Project Construction • Cadsoft’s Eagle for schematic design and PC board layout • Advanced Circuits and ECE shop for board layout • Parts ordered from: • Transducers Direct (timer chips) • Digi-Key • Mouser • Newark • ECE shop • Professor Kwiat • Circuit boards hand soldered • Hakko 936-12 ESD safe iron • Kester no clean flux pen • Kester no clean solder • fine tweezers for component placement

8. In a nutshell…

9. Laser Driver Objective & Parameters • Objective • Drive the Laser Diode with crisp “square” pulses • Parameters • High Speed Data In • Quick Rise and Fall Time • Drive 90 mA for Laser Diode • Low Noise

10. Laser Driver Circuit – Concept Art

11. Board Layout

12. Final Product

13. Transmit Optics (Complete) • Requirements: • Collimated beam • Optimum power match up with laser driver • Wavelength matching up with receiver optics • Fast rise time

14. Receiver Optics (Incomplete) • Requirements: • Detection of scattered beamfrom object and discrimination of ambient light. • Accurate and constant time spent on sending signal to timing circuit. • Fast rise and fall times that allow for higher precision in laser range finder.

15. Optics Results

16. Timing Circuit Objectives • Circuit that can measure time lapsed between rising edges of two pulses • To be used for measuring time of flight of laser pulses • Measure the time span between outgoing laser pulse and incoming received laser pulse • Goal is 1cm resolution • For quantum cryptography random number generator: • Needs to measure time span between pulses all on the same line • Needs approximately 200ps resolution. • Needs to be ready for a new sample within about 20ns of receiving previous sample

17. Resolution • For Laser scanning circuit, we want 1cm resolution • Speed of light is 299792458 m/s • Thus, we theoretically need resolution of .01 * 2 * 299792458 m/s = 67ps • This makes assumption all other components are perfect • Since all components are not perfect – we need better than 67ps resolution • For Prof. Kwiat’s quantum cryptography circuit, we need about 200 ps resolution, so this easily falls within laser range finder design parameters

18. Timing Circuit Considered • Discrete timing circuit • Acam TDC-GP2 • Acam TDC-GPX

19. Discrete Timing Circuit • Start signal latched D-latch so that mosfet turns on, charging C through an RC circuit • Stop signal un-latches D-latch so that mosfet turns off, stopping the charging of C • ADC then reads in voltage across capacitor, and then can find amount of time spent charging capacitor by extrapolating it from Vc = 5 * (1-e^(t/(RC) ) ) • Unfortunately, propagation delay and gate capacitances of components completely destroys accuracy and resolution of such a circuit

20. Discrete Timer Schematic

21. Acam TDC-GP2 • Special purpose timing chip designed to measure the amount of time that elapsed between a start pulse and a stop pulse • Somewhat low cost - $28/chip • 50 ps resolution • Very small QFN 32 package • Fairly simple external components needed • SPI interface • Runs at up to 25MHz • Would take approximately 1µs to read out data • Fast enough for laser range finder • Too slow for random number generator

22. Acam TDC-GPX • Special purpose timing chip designed to measure the amount of time that elapsed between a start pulse and a stop pulse • High cost - $187/chip • 10 ps resolution • 100 TQFP package • Very complicated external components needed • High speed parallel interface • Easily fast enough for both random number generator and laser range finder

23. Final Decision • Our choice: • We chose to use the Acam TDC-GPX • Though the other two circuits considered would have been considerably easier to design, build, and debug, this was the only way for us to meet Prof. Kwiat’s needs • Parameters for TDC-GPX schematic design: • Ultra clean power supply • Minimal part count • Parts with small footprints • Singled ended and differential start and stop signals

24. Final schematic:

25. Parameters for TDC-GPX board design • Maximize size and integrity of ground plane • Minimize noise on signal traces • Minimize all trace lengths, especially signal and analog traces • Traces that have to cross over each other should be perpendicular • Match impedances and trace lengths of differential signals

26. Final board design

27. Final board top

28. Final board bottom

29. Final PCB Top

30. Final PCB Bottom

31. Control Module (Complete) • Requirements: • Provide successful start up of laser driver and TDC-GPX. • Provide successful interaction between the laser driver and the TDC-GPX. • Program onto a Spartan-3 for this interaction • Serial communication with computer to send timing information.

32. Control Module -- Timing Circuit Pseudo Code &Laser Driver State Diagram

33. Laser Driver State Machine

34. Control Module Results

35. Cost Analysis – Software (COCOMO) Effort Adjustment Factor (EAF) Rating : 1.14 • Organic Software Project • Coefficient ‘a’ = 2.4 • Exponent ‘b’ = 1.05 • Size of software = 6 K Lines of Code • Effort = [ a (Size)b ] (EAF) = 17.95 person-months • Software Development time = Effort/people = 4.49 months • 4.49 months * (60 hours/month labor) ($ 60 / hour) (3 people) • Labor Cost = $ 48.5K • Without Makela’s proposed 2.5 estimation factor

36. Cost Analysis – Hardware Costs and Labor • Parts Cost : $377.33 • Basic Electronic Components (Resistors, Capacitors, etc) - $35.00 • TDX-GPX - $187.00 • Vertical SMA Connector – $5.94 • Circuit Board - $33.00 • Photodiode - $6.14 • Laser Diode - $5.00 • Spartan 3 FPGA - $100.00 • AND 2870 - $5.25 • Hardware Labor Costs and Estimation • (160 hours) ( $60/hour) (3 people) • Labor = $28.8K • Total Costs = Software Labor + Hardware Labor + Parts = $77677.33

37. “Success consists of going from failure to failure without loss of enthusiasm.” -- Winston Churchill

38. Successes • Laser Driver Circuit Design and Layout • Transmit Optics • Timing Circuit • Control Module

39. Shortcomings • Laser Driver Circuit • High Speed Circuit • Extremely Sensitive • Receiver Optics • Breadth of work needed to build a proper receiver circuit was underestimated. • Misrecognition of primary task. • Failure to identify primary task within time frame to allow successful completion of this portion of the project. • Timing Circuit • Complex Circuit • Research • Complex Board Layout • High Speed Circuit

40. Special Thanks Special thanks goes to: • Professor Kwiat • Evan Jeffrey • Mark Smart • Dr. Peter Dragic • Dr. Stephen Bishop • Michael Zhang

41. Question and Answer