1. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-1 ECEG287 Optical Detection Course Notes Part 9: Detector as a Circuit Element Profs. Charles A. DiMarzio and Stephen W. McKnight Northeastern University, Spring 2004

2. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-2 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

3. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-3 The Basic Model t p Incident Light: Detector and Bias Circuit t V Output Signal:

4. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-4 Bias Circuits The Bias Tee Transimpedance Amplifier Balanced Bridge Photovoltaic Mode

5. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-5 The Photodiode Current Responsivity 

6. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-6 Photodiode Model C

7. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-7 Photodiode I-V Curves

8. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-8 Conventional Bias Circuit DC Current (Dark and Bias) From AC Signal Power t p Incident Light: C

9. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-9 Response to Varying Power t t

10. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-10 DC Analysis Set Operating Point V_V1 -10V-5V0V5V -I(R1) -5.0mA 0A 5.0mA X X X Choose Load Line to Maximize Voltage Swing Avoid Saturation Allow for DC Variations 3ma

11. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-11 AC Analysis V_V1 -10V-5V0V5V -I(R1) -5.0mA 0A 5.0mA X X AC Load Line May be Different from DC

12. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-12 Transient Analysis of AC Signal I_I1 0A2mA4mA6mA8mA10mA V(R1:2) -10V 0V 10V Voltage Across Diode Time 0s0.2us0.4us0.6us0.8us1.0us V(R2:2) -40mV 0V 40mV i P (DC) =6.0mA 6.5mA 7mA Load Voltage

13. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-13 Saturation at High Power Voltage Goes to Zero Solutions –Lower Resistor –Higher Supply Voltage V_V1 -I(R1) -10V-5V0V5V -5.0mA 0A 5.0mA

14. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-14 Transimpedance Amplifier -10V-5V0V5V -5.0mA 0A 5.0mA Virtual Ground acts as a 0-Ohm Load Resistor (Prevents Saturation) Time 0s0.2us0.4us0.6us0.8us1.0us V(D1:1)V(U1:OUT) -4.0V -2.0V 0V

15. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-15 Balanced Bridge Circuit Time 0s0.2us0.4us0.6us0.8us1.0us V(RL:2) -500mV 0V 500mV R1, R2 Set Diode Bias Voltage RNull Nulls out Background and Current through RF -10V-5V0V5V -5.0mA 0A 5.0mA

16. February 2004 Charles A. DiMarzio, Northeastern University 10464-9-16 Photovoltaic Mode V_V1 -1.0V-0.5V0V0.5V1.0V -I(R1) -5.0mA 0A 5.0mA 200 Ohms P=IV<0