Datasheet

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SBOS301A − MAY 2004 − REVISED MARCH 2007
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17
NEGATIVE INPUT CURRENTS
The LOG114 functions only with positive input currents
(conventional current flows into input current pins). In
situations where negative input currents are needed,
the example circuits in Figure 7, Figure 8, and Figure 9
may be used.
Q
B
National
LM394
I
IN
I
OUT
D
1
OPA703
D
2
Q
A
Figure 7. Current Inverter/Current Source.
1.5k
Ω
Photodiode
10nA to 1mA
10nA to 1mA
+5V
+5V
1k
Ω
+3.3V
1/2
OPA2335
1/2
OPA2335
BSH203
(+3.3V
Back Bias)
LOG114
Pin3orPin4
Figure 8. Precision Current Inverter/Current Source.
1k
Ω
+5V
+5V
1.5k
Ω
1.5k
Ω
100k
Ω
10nA to 1mA +3.3V
LOG114
10nA to 1mA
100k
Ω
100k
Ω
+3.3V
1/2
OPA2335
1/2
OPA2335
Photodiode
Back Bias
Pin 3 or Pin 4
100k
Ω
Figure 9. Precision Current Inverter/Current Source.