Download Lecture Notes 9 - Detectors as Circuit Elements

ECEG287
Optical Detection Course Notes
Part 9: Detector as a Circuit
Element
Profs. Charles A. DiMarzio
and
Stephen W. McKnight
Northeastern University, Spring 2004
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-1
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
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-2
The Basic Model
Incident Light:
p
t
February 2004
Detector
and Bias
Circuit
Charles A. DiMarzio, Northeastern University
Output Signal:
V
t
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Bias Circuits
•
•
•
•
The Bias Tee
Transimpedance Amplifier
Balanced Bridge
Photovoltaic Mode
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-4
The Photodiode
• Current Responsivity
dQ
e dE
e
iP 
 q
 q
p  i p
dt
h dt
h
5.0mA
e
i  q
h
0A

-5.0mA
-10V
l
February 2004
Charles A. DiMarzio, Northeastern University
-5V
0V
-I(R1)
V_V1
5V
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Photodiode Model
C
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-6
Photodiode I-V Curves
5.0mA
0A
-5.0mA
-10V
-8V
-6V
-4V
-2V
0V
2V
-I(R1)
V_V1
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-7
Conventional Bias Circuit
Incident Light:
p
t
From AC
Signal
Power
C
DC
Current
(Dark and
Bias)
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-8
Response to Varying Power
5.0mA
0A
t
-5.0mA
-10V
-8V
-6V
-4V
-2V
0V
2V
-I(R1)
February 2004
t
V_V1
Charles A. DiMarzio, Northeastern University
10464-9-9
DC Analysis Set Operating Point
5.0mA
X
0A
X
3ma
-5.0mA
X
-10V
-5V
0V
-I(R1)
V_V1
5V
Choose Load Line to
Maximize Voltage Swing
Avoid Saturation
Allow for DC Variations
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-10
AC Analysis
5.0mA
0A
X
X
-5.0mA
-10V
-5V
0V
-I(R1)
V_V1
5V
AC Load Line May be Different
from DC
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-11
Transient Analysis of AC Signal
10V
Voltage Across Diode
0V
-10V
0A
2mA
4mA
V(R1:2)
I_I1
6mA
8mA
10mA
40mV
Load Voltage
0V
iP(DC)=6.0mA
7mA
6.5mA
-40mV
0s
February 2004
0.2us
V(R2:2)
0.4us
Time
0.6us
Charles A. DiMarzio, Northeastern University
0.8us
1.0us
10464-9-12
Saturation at High Power
5.0mA
• Voltage Goes to Zero
• Solutions
0A
-5.0mA
– Lower Resistor
– Higher Supply Voltage
-10V
40mV
Load Voltage
0V
-5V
0V
-I(R1)
V_V1
5V
iP(DC)=6.0mA
7mA
6.5mA
-40mV
0s
February 2004
0.2us
V(R2:2)
0.4us
0.6us
Time
Charles A. DiMarzio, Northeastern University
0.8us
1.0us
10464-9-13
Transimpedance Amplifier
Virtual Ground acts as
a 0-Ohm Load Resistor
(Prevents Saturation)
5.0mA
0A
-5.0mA
-10V
-5V
0V
5V
0V
-2.0V
-4.0V
0s
V(D1:1)
0.2us
V(U1:OUT)
0.4us
0.6us
0.8us
1.0us
Time
February 2004
Charles A. DiMarzio, Northeastern University
10464-9-14
Balanced Bridge Circuit
5.0mA
0A
-5.0mA
-10V
-5V
0V
5V
500mV
0V
R1, R2 Set Diode Bias Voltage
RNull Nulls out Background
and Current through RF
February 2004
-500mV
0s 0.2us 0.4us 0.6us 0.8us1.0us
V(RL:2)
Time
Charles A. DiMarzio, Northeastern University
10464-9-15
Photovoltaic Mode
5.0mA
P=IV<0
0A
-5.0mA
-1.0V -0.5V
February 2004
200 Ohms
0V 0.5V 1.0V
-I(R1)
V_V1
Charles A. DiMarzio, Northeastern University
10464-9-16