Download Power Supply Circuit

Visible Light Photon Counter Integrator
Group 48: Katie Nguyen, Austin Jin
ECE445 Spring 2016
May 1, 2016
Motivation
 Optical Quantum Information [1]
– Quantization of detected photons
– Quantum communication: Using properties of photons to securely store and
transmit information
Introduction
 Proposed project by Professor Kwiat
 Current method: threshold method
 Proposed method: integration method
Example of Photon Pulse in MATLAB
 Pulse height ~-150mV * n for n incident photons
Figure 1: One photon per pulse
Figure 2: Two photons per pulse
Example of Photon Pulse in MATLAB
 Worst case example
Figure 3: Two photons overlapping
Figure 4: Three photons overlapping
Objectives
 More precise method of calculating number of photons per pulse
– Distinguish between 1 – 5 photons per pulse
– Synchronized Integrator with External Trigger
 Make integral accessible through device for further processing.
 Add Features for Readability
– Graphical User Interface
– Logging capabilities
Diagram of Design
Figure 5: Block diagram
Integrator Circuit
Figure 6: Integrator circuit diagram
Integrator Output Calculations
Integrator Simulation Results
R (Ω)
Calc (mV)
Sim (mV)
% diff
50
150
144.74
3.507
100
75
73.52
1.973
200
37.5
37.05
1.2
500
15
14.89
0.733
1K
7.5
7.458
0.56
5K
1.5
1.493
0.467
10K
0.75
0.7468
0.427
Figure 7: Integrator simulation
 Simulated voltage is measured at 10 ns
Table 1: Integrator simulation result
Integrator Simulation Results
 Unstable when capacitance is larger than 100 pF
Figure 8: Integrator simulation at 1nF
Figure 9: Single integrator simulation at 1nF
Power Supply Circuit
 Input: 120V AC wall outlet
– Stepped down to 12V AC via center-tapped transformer
– Full-wave rectified
– Linear regulators on PCB
 Provide a set of stable voltages
– +/- 2.5V to the integrator circuit
– 3V to the ADC
Power Supply Circuit
Transformer
Rectifier/Smoothing caps
Figure 10: Power supply circuit
 The constant current load assumed
Regulators
Power Supply Simulations
 Voltage level at +/- 2.5V, 3V
 Negligible ripples
 Stable level achieved by 1ms
Figure 11: Power supply simulation
Power Supply Setup
Figure 13: Power supply PCB
Figure 12: Transformer top-view (top) and front-view (bottom)
Power Supply Results
Designed Output (V) Actual Output (V)
% Difference
-2.5
-2.488
0.48
2.5
2.268
9.28
3
2.986
0.56
Table 2: Power supply results
 Possible explanation for 2.5V
– PCB burned during testing, due to narrow traces
 Should not matter if within the amplifier operational range
ADC for Post-Processing
 Considerations for Design
– Fast enough to accurately sample within a narrow window
– High Speed ADCs are Expensive
• Minimum Speed To Sample
• Minimum Resolution
ADC for Post-Processing
 Decision for Design
Figure 14 : TI ADC08200
– ADC08200-200Msps will allow us to sample for a 5ns duration
• frequency = 1/time = 1/5E-9s = 2E8s = 200Msps
– ADC08200 –8 bit ADC IC will accept a voltage range of 0-3.3V
• Voltage Resolution = (3.3V - 0V) / 256 bits = 12.94 mV/bit
– This tells us that an 8 bit ADC will give us enough resolution to discriminate
one photon from another.
Proposed Post-Processing Setup
 Simulate Laser Source for 0-10
Photons Per Pulse in Matlab
 Integrate Pulses in Matlab
 Feed Integrated Pulses using a
Function Generator into ADC
Figure 15 : Flowchart of Experimental
Setup
Example of Integral in MATLAB
 Each photon generates a fixed amount of charge.
Figure 16 : Integral of One Photon
Figure 17: Integral of Two Photons
Post-Processing (Software)
 Use WiringPi to Allow
Communication with BCM2835 on
Raspberry Pi (8 bit data lines)
 Enable Serial Peripheral Interface
(SPI) bus for SCLK access
 QT Framework for Graphical User
Interface
Figure 18 : Flow Chart of Post Processing
Post-Processing Results
Figure 19 : VLPC GUI
Figure 20 : VLPC Log File
Post-Processing Results
Figure 21 : No photons
Figure 22 : One photons
Figure 22 : Two photons
Challenges
 Precisely Synchronize Sampling with Trigger
– Missing Photon Pulse
 Account for Large Quantity of Noise
– Mindful of Width of PCB Traces
– Impedance matching
Conclusion
 Extensive research on a working design
 Delivered on proposed features
– Graphical user interface
– Log file
 Future work : integrator circuit hardware– in progress
LTC6409
Figure 23 : DC2266A Schematic (LTC6409 demo board)
Special Thanks




Ankit (TA)
Dr. Sahoo and Dr. Hanumolu
Professor Kwiat
Fumihiro Keneda (Post-Doc)
Questions?
References
 [1] "New nanodevice shifts light's color at single-photon level",
Phys.org, 2016. [Online]. Available: http://phys.org/news/201604-nanodevice-shifts-single-photon.html. [Accessed: 30- Apr2016].