LOG104_14 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
2.0
V_OUT = 0.5V LOG (I₁/I₂)
1.5
1.0
0.5
0.0
–0.5
–1.0
–1.5
–2.0
0.0001 0.001 0.01 0.1 1 10 100 1k 10k
Current Ratio, I₁/I₂
TOTAL ERROR vs INPUT CURRENT
120
100
+75°C
80
60
40
+25°C –5°C
20
0
100pA 1nA 10nA 100nA 1µA 10µA 100µA 1mA 10mA
Input Current (I₁ or I₂)
ONE CYCLE OF NORMALIZED TRANSFER FUNCTION
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
1
2
3
4
6
8 10
Current Ratio, I₁/I₂
GAIN ERROR (I₂ = 1µA)
5.8
+85°C
4.8
+75°C
3.8
+25°C
2.8
–5°C to –40°C
1.8
0.8
–0.2
100pA 1nA
10nA 100nA 1µA 10µA 100µA 1mA 10mA
Input Current (I₁ or I₂)
100M
10M
1M
100k
10k
1k
MINIMUM VALUE OF COMPENSATION CAPACITOR
Select C_C for I₁ min.
and I₂ max. Values
below 2pF may be ignored.
I₁ = 100pA
I₁ = 1nA
I₁ = 10nA
I₁ = 100nA
1µA
100
10
1
100pA
1nA 10nA 100nA 1µA
I₂
I₁ = 10µA
100µA
1mA
10µA 100µA 1mA 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
1
= ^1000pF
CC
= ^1µF
CC
0.1
100pA 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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LOG104
SBOS243C