Datasheet

PHOTO DIODE
PRESENTATION
I
IN
C
D
R
F
C
F
+
-
V
OUT
V
OUT
= -I
IN
* R
F
+
-
R
IN
75:
R
G
250:
R
F
250:
10nF
C3
C4
6.8PF
R
OUT
75:
6.8PF
10nF
C2
C1
V
OUT
+
V
S
R
S
75:
LMH6609
SNOSA84F –AUGUST 2003–REVISED MARCH 2013 www.ti.com
Figure 37. Typical Video Application
ESD PROTECTION
The LMH6609 is protected against electrostatic discharge (ESD) on all pins. The LMH6609 will survive 2000V
Human Body model or 200V Machine model events.
Under closed loop operation the ESD diodes have no effect on circuit performance. There are occasions,
however, when the ESD diodes may be evident. For instance, if the amplifier is powered down and a large input
signal is applied the ESD diodes will conduct.
TRANSIMPEDANCE AMPLIFIER
The low input current noise and unity gain stability of the LMH6609 make it an excellent choice for
transimpedance applications. Figure 38 illustrates a low noise transimpedance amplifier that is commonly
implemented with photo diodes. R
F
sets the transimpedance gain. The photo diode current multiplied by R
F
determines the output voltage.
Figure 38. Transimpedance Amplifier
The capacitances are defined as:
• C
D
= Equivalent Diode Capacitance
• C
F
= Feedback Capacitance
The feedback capacitor is used to give optimum flatness and stability. As a starting point the feedback
capacitance should be chosen as ½ of the Diode capacitance. Lower feedback capacitors will peak frequency
response.
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