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Optical Detection: Detector as a Circuit Element

This course material discusses the various aspects of using a detector as a circuit element in optical detection, including dark current, photocurrent, operating point, capacitance, impedance, and power dissipation.

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Optical Detection: Detector as a Circuit Element

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  1. ECEG287 Optical Detection Course NotesPart 9: Detector as a Circuit Element Profs. Charles A. DiMarzio and Stephen W. McKnight Northeastern University, Spring 2004 Charles A. DiMarzio, Northeastern University

  2. Some of the Issues • Dark Current • Photocurrent • DC Current (Mean Power in Signal) • Operating Point • Capacitance (Maintain Reverse Bias) • DC and AC Impedance • Power Dissipation Charles A. DiMarzio, Northeastern University

  3. The Basic Model Incident Light: Output Signal: Detector and Bias Circuit p V t t Charles A. DiMarzio, Northeastern University

  4. Bias Circuits • The Bias Tee • Transimpedance Amplifier • Balanced Bridge • Photovoltaic Mode Charles A. DiMarzio, Northeastern University

  5. 5.0mA 0A -5.0mA -10V -5V 0V 5V -I(R1) V_V1 The Photodiode • Current Responsivity r l Charles A. DiMarzio, Northeastern University

  6. Photodiode Model C Charles A. DiMarzio, Northeastern University

  7. 5.0mA 0A -5.0mA -10V -8V -6V -4V -2V 0V 2V -I(R1) V_V1 Photodiode I-V Curves Charles A. DiMarzio, Northeastern University

  8. Conventional Bias Circuit Incident Light: p t From AC Signal Power C DC Current (Dark and Bias) Charles A. DiMarzio, Northeastern University

  9. 5.0mA 0A -5.0mA -10V -8V -6V -4V -2V 0V 2V -I(R1) V_V1 Response to Varying Power t t Charles A. DiMarzio, Northeastern University

  10. DC Analysis Set Operating Point 5.0mA X 0A X 3ma -5.0mA X -10V -5V 0V 5V -I(R1) V_V1 Choose Load Line to Maximize Voltage Swing Avoid Saturation Allow for DC Variations Charles A. DiMarzio, Northeastern University

  11. AC Analysis 5.0mA 0A X X -5.0mA -10V -5V 0V 5V -I(R1) V_V1 AC Load Line May be Different from DC Charles A. DiMarzio, Northeastern University

  12. Transient Analysis of AC Signal 10V Voltage Across Diode 0V -10V 0A 2mA 4mA 6mA 8mA 10mA I_I1 V(R1:2) 40mV Load Voltage iP(DC)=6.0mA 7mA 0V 6.5mA -40mV 0s 0.2us 0.4us 0.6us 0.8us 1.0us Time V(R2:2) Charles A. DiMarzio, Northeastern University

  13. 5.0mA 0A -5.0mA -10V -5V 0V 5V 40mV Load Voltage iP(DC)=6.0mA 7mA 0V 6.5mA -40mV 0s 0.2us 0.4us 0.6us 0.8us 1.0us Time V(R2:2) Saturation at High Power • Voltage Goes to Zero • Solutions • Lower Resistor • Higher Supply Voltage -I(R1) V_V1 Charles A. DiMarzio, Northeastern University

  14. 5.0mA 0A -5.0mA -10V -5V 0V 5V Transimpedance Amplifier Virtual Ground acts as a 0-Ohm Load Resistor (Prevents Saturation) 0V -2.0V -4.0V 0s 0.2us 0.4us 0.6us 0.8us 1.0us V(D1:1) V(U1:OUT) Time Charles A. DiMarzio, Northeastern University

  15. 5.0mA 0A -5.0mA -10V -5V 0V 5V Balanced Bridge Circuit 500mV 0V R1, R2 Set Diode Bias Voltage RNull Nulls out Background and Current through RF -500mV 0s 0.2us 0.4us 0.6us 0.8us 1.0us V(RL:2) Time Charles A. DiMarzio, Northeastern University

  16. Photovoltaic Mode 5.0mA P=IV<0 0A -5.0mA 200 Ohms -1.0V -0.5V 0V 0.5V 1.0V -I(R1) V_V1 Charles A. DiMarzio, Northeastern University

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