LOG100 Datasheet, PDF (4/9 Pages) Burr-Brown (TI) – Precision LOGARITHMIC AND LOG RATIO AMPLIFIER

TYPICAL PERFORMANCE CURVES
T_A = +25°C, V_CC = ±15VDC, unless otherwise noted.
NORMALIZED TRANSFER FUNCTION
3 (K)
2 (K)
1 (K)
0 (K)
–1 (K)
–2 (K)
–3 (K)
V_OUT = K Log
I₁
I₂
0.001 0.01
0.1 1 10
Current Ratio, ^I1
I₂
100 1000
TOTAL ERROR vs INPUT CURRENT
±75
±50
±25
0
1nA
100nA
10µA
Input Current ( I₁ or I₂)
1mA
ONE CYCLE OF NORMALIZED TRANSFER FUNCTION
1 (K)
0.9 (K)
0.8 (K)
0.7 (K)
0.6 (K)
0.5 (K)
0.4 (K)
0.3 (K)
0.2 (K)
0.1 (K)
0
1
2
3
4
6
8 10
Current Ratio, ^I1
I₂
TRIMMED OUTPUT ERROR vs INPUT CURRENT
60
–60
Gain Error and
50 Offset Error Trimmed
–50
to Zero
40
–40
30
–30
20
–20
10
–10
0
0
–10
–20
1nA
100nA
10µA
Input Current (I₁ or I₂)
10
20
1mA
1M
100k
10k
1k
MINIMUM VALUE OF COMPENSATION CAPACITOR
Select C_C for
I₁ min and I₂ max
I₁ = 1nA
I₁ = 10nA
Values below 2pF ^{I1 = 100nA}
may be ignored.
100
I₁ = 1µA
I₁ = 10µA
10
1
I₁ = 100µA to 1mA
1nA 10nA 100nA 1µA 10µA 100µA 1mA
Input Current, I₂
1M
100k
3dB FREQUENCY RESPONSE
10µA
1µA
10k
1k
100µA
1nA
= ^{10pF 100µA}
CC
10µA ^{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
®
LOG100
4