Datasheet

LOG112, 2112
10
SBOS246D
www.ti.com
FIGURE 11. Single +5V Power-Supply Operation.
14
1
5
10
6
9
1
2
35
4
–5V
1µF
LOG112
1µF
I
1
I
2
V
LOGOUT
C
C
1µF
TPS
(1)
Single Supply +5V
NOTE: (1) TPS60402DBV
negative charge pump.
FIGURE 10. Absorbance Measurement.
I
2
I
1
14
1
9
10
5
V
LOGOUT
6
V+
V–
C
C
LOG112
D
2
D
1
Sample
λ
1
λ
1
´
λ
1
Light
Source
DATA COMPRESSION
In many applications, the compressive effects of the logarith-
mic transfer function are useful. For example, a LOG112
preceding a 12-bit A/D converter can produce the dynamic
range equivalent to a 20-bit converter.
OPERATION ON SINGLE SUPPLY
Many applications do not have the dual supplies required to
operate the LOG112 and LOG2112. Figure 11 shows the
LOG112 and LOG2112 configured for operation with a single
+5V supply.
MEASURING AVALANCHE PHOTODIODE CURRENT
The wide dynamic range of the LOG112 and LOG2112 is
useful for measuring avalanche photodiode current (APD), as
shown in Figure 12.
FIGURE 12. High-Side Shunt for APD Measures 3 Decades of APD Current.
A
1
–5V
SO-14
91113
LOG112
Q
1
2
Q
2
I
OUT
I
OUT
= 0.1 • I
SHUNT
10 3
4
10kΩ
Receiver
Irx = 1µA to 1mA
I-to-V
Converter
APD
10Gbits/sec
16.7kΩ
C
C
A
2
A
3
V
03
= 2.5V to 0V
I
SHUNT
500Ω
5kΩ 5kΩ
+15V to +60V
+5V
INA168
SOT23-5
+5V
1
1
14
8
6
5
7
100µA
25kΩ
V
REF