LOG102 Datasheet, PDF (4/15 Pages) Texas Instruments – LOGARITHMIC AND LOG RATIO AMPLIFIER

TYPICAL CHARACTERISTICS
At T_A = +25°C, V_S = ±5V, R_L = 10kΩ, unless otherwise noted.
NORMALIZED TRANSFER FUNCTION
3
V_OUT = 1V • Log
I₁
I₂
2
1
0
–1
–2
–3
0.001 0.01
0.1
1
10
Current Ratio, ^I1
I₂
100 1000
ONE CYCLE OF NORMALIZED TRANSFER FUNCTION
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1
2
3
4
6
8 10
Current Ratio, ^I1
I₂
TOTAL ERROR vs INPUT CURRENT
60
50
40
30 _0°C
20
10
70°C
25°C
0
1nA
10nA
100nA 1µA 10µA
Input Current
(I₁ or I₂)
100µA
1mA
GAIN ERROR vs TEMPERATURE
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
–0.05
–0.10
–60 –40 –20
0
20
40
60
80
Temperature (°C)
10000
1000
100
10
MINIMUM VALUE OF COMPENSATION CAPACITOR
Select C_C for I₁ min
and I₂ max
I₁ = 1nA
I₁ = 10nA
I₁ = 100nA
I₁ = 1µA
I₁ = 10µA
I₁ = 1mA
I₁ = 100µA
1
1nA
Values below 2pF
may be ignored.
10nA 100nA
1µA 10µA 100µA 1mA
I₂
10mA
1M
100k
3dB FREQUENCY RESPONSE
10µA
1µA
10k
1k
100µA
1nA
= ^{10pF 100µA}
CC
10^{µA to 1µA}
10nA
10nA
100
I₁ = 1nA
10
= ^1000pF
1
CC
0.1
= ^1µF
C^C
1nA 10nA 100nA 1µA 10µA 100µA
I₂
100µA
100µA
1mA
I₁ = 1mA
1µA
1mA
to 10µA
100nA
10nA
I₁ = 1nA
1mA
4
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LOG102
SBOS211A