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Black Box Electronics

Black Box Electronics. An Introduction to Applied Electronics for Physicists 4. Sample Circuits University of Toronto Quantum Optics Group Alan Stummer, Research Lab Technologist. Sample Circuits. General Coil switch LED switch Analog Photodiode monitor (transimpedance amp)

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Black Box Electronics

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  1. Black Box Electronics An Introduction to Applied Electronics for Physicists 4. Sample Circuits University of Toronto Quantum Optics Group Alan Stummer, Research Lab Technologist

  2. Sample Circuits • General • Coil switch • LED switch • Analog • Photodiode monitor (transimpedance amp) • Linear laser driver • Hybrid • Planar triode grid pulse, for Pockels cell.

  3. Coil Switch • D1 is “flyback” diode, to absorb energy from coil when Q1 turns off. Without it, Q1 would be destroyed the first time it turns off. • R1 forces Q1 into cutoff if nothing connected to BNC. • Q1 is “logic level” – VGS(thresh) is ≤ +2V, the minimum TTL high voltage.

  4. LED Switch • Separate resistors R3-4 because voltage drop across each LED chain is not identical. Single resistor would result in deterministic total current but indeterminate current distribution. • R3 and R4 voltages are 10V – 5*1.5V, therefore ILED = 50mA. • Can ignore Q2’s RDS(on) of 0.025Ω(max) at VGS = +5V, insignificant compared to R3-4.

  5. Photodiode Monitor”Transimpedance Amplifier, TIA” • PD1 generates current at typically 0.5-1A/W. • Current generated by PD1 is mirrored through R5 by IC1. • Full scale is 5V (5mA, ~5mW). • Bandwidth (rise & fall times) set by C1 and R5, here 68KHz. • C1 is mandatory to prevent positive feedback (oscillation) from PD1’s capacitance. • Slightly slow response by PD1 as is. Add reverse bias of several volts to reduce junction capacitance for faster response.

  6. Linear Laser Driver • Stable reference voltage of +1.25V set by IC3, proportion taken by pot R6. • IC5 turns on Q3 enough so that the laser current through R9 creates the same voltage across R9 as from R6. • IC5 integrates error current from R7 through C5; forces IC5 to be IR7 until both are zero. • R10 is protection against excess laser current, C6 provides noise and EMI filtering.

  7. How [not] To Develop a Circuit

  8. FPGA Development Overview Experiment GUI Software FPGA Firmware PCB (Hardware) DACs ADCs FPGA Config Chip Computer IDE Quartus (Realtime) Active Serial Port USB Port 100MHz Clock USB Blaster (needed for changes only)

  9. FPGA Pockels Cell Controller Development Sequence • Write and simulate firmware, select FPGA (Quartus). • Design circuit – A.K.A. schematic capture (Eagle). • Layout PCB – A.K.A. CAD (Eagle). • Order components, then PCB. • Assemble and test supplies, assemble remainder. • Load config chip. • Write software/GUI (LabView/Windows, VisualC/Basic). • Test hardware, firmware and software. • Modify hardware, firmware and/or software, reload config chip. • Repeat 8-9 ad nauseam or until can go no further. • Spin (revise and reorder) PCB, repeat from 4.

  10. FPGA Based Pockels Cell Driver • FPGA is used for speed and complexity – 5nS resolution over 100mS cycle. • FPGA IC9 uses “config chip” IC5 for program and clock IC6. • Config chip is programmed via “Active Serial” connector J3. • FPGA has multiple I/Os to DACs and LEDs. • FPGA has 16-bit bi-directional bus with USB interface IC12, for control and monitoring. • Power supplies not shown: +3.3V and +1.5V.

  11. Suggested Components

  12. Ω The End Ω Next: 5. Need suggestions for subject(s) to focus on: Spice (circuit simulation)? Op Amps? Transistors? FPGAs? More sample circuits? Power supplies? Micros? Thanks for coming!

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