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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
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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
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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:
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February 2004 Charles A. DiMarzio, Northeastern University 10464-9-4 Bias Circuits The Bias Tee Transimpedance Amplifier Balanced Bridge Photovoltaic Mode
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February 2004 Charles A. DiMarzio, Northeastern University 10464-9-5 The Photodiode Current Responsivity
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February 2004 Charles A. DiMarzio, Northeastern University 10464-9-6 Photodiode Model C
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February 2004 Charles A. DiMarzio, Northeastern University 10464-9-7 Photodiode I-V Curves
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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
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February 2004 Charles A. DiMarzio, Northeastern University 10464-9-9 Response to Varying Power t t
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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
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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
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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
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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
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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
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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
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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
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