Datasheet

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LOG101
10
SBOS242B
(10)
FIGURE 14. High Side Shunt for Avalanche Photodiode (APD) Measures 3-Decades of APD Current.
A
1
–5V
SO-8
5
LOG101
Q
1
2
Q
2
I
OUT
I
OUT
= 0.1 • I
SHUNT
6
1.2kΩ
Receiver
Irx = 1µA to 1mA
I to V
Converter
APD
10Gbits/sec
1kΩ
C
C
A
2
OPA703
V
OUT
= 2.5V to 0V
I
SHUNT
100µA
500Ω
5kΩ 5kΩ
+15V to +60V
+5V
25kΩ
INA168
SOT23-5
REF3025
2.5V
+5V
1
1
8
4
3
The individual component of error is:
∆K = gain accuracy (0.15%, typ), as specified in the
specification table.
I
B1
= bias current of A
1
(5pA, typ)
I
B2
= bias current of A
2
(5pA, typ)
N = log conformity error (0.01%, 0.06%, typ)
0.01% for n = 5, 0.06% for n = 7
V
OSO
= output offset voltage (3mV, typ)
n = number of decades over which N is specified:
Example: what is the error when
I
1
= 1µA and I
2
= 100nA
VmV
OUT
=±
(
)
−
−
±
(
)
(
)
±
−−
−−
1 0 0015
10 5 10
10 5 10
2 0 00015 3 0
612
712
.log
•
•
..
= 1.005055V
(11)
(12)
(13)
Since the ideal output is 1.000V, the error as a percent of
reading is
%
.
%.%error =•=
0 005055
1
100 0 5
For the case of voltage inputs, the actual transfer function is
VVK
V
R
I
E
R
V
R
I
E
R
Nn V
OUT
B
OS
B
OS
OSO
=
(
)
±
(
)
±
±
±±11 2
1
1
1
1
1
2
2
2
2
2
∆ log
–
–
Where
E
R
and
E
R
OS OS1
1
2
2
are considered to be zero for large
values of resistance from external input current sources.