LOG112AIDE4 Datasheet, PDF (10/20 Pages) Texas Instruments – Precision LOGARITHMIC AND LOG RATIO AMPLIFIERS

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.
Sample
λ₁
λ ₁´
Light ^λ1
Source
V+
I_{1 1}
6
D₁
I_{2 14}
D₂
LOG112
9
C_C
V–
FIGURE 10. Absorbance Measurement.
5
V_LOGOUT
10
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.
Single Supply +5V
6
1
5
V_LOGOUT
I₁
14
I₂
1µF
3
5
2
1
TPS⁽¹⁾
1µF
4
LOG112
10
9
C_C
–5V
1µF
NOTE: (1) TPS60402DBV
negative charge pump.
FIGURE 11. Single +5V Power-Supply Operation.
+15V to +60V
500Ω
I_SHUNT
5kΩ
5kΩ
+5V
INA168
SOT23-5
2
1
I_OUT
I_OUT = 0.1 • I_SHUNT
+5V
6
1
Q₁
C_C
Q₂
A₁
Irx = 1µA to 1mA
Receiver
APD
I-to-V
Converter
10Gbits/sec
10kΩ
16.7kΩ
5
A₂
4
7
A₃
V₀₃ = 2.5V to 0V
100µA
14
25kΩ
8
V_REF
SO-14
9 11 13
–5V
LOG112
10
3
FIGURE 12. High-Side Shunt for APD Measures 3 Decades of APD Current.
10
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LOG112, 2112
SBOS246D