TL441-EP_14 Datasheet, PDF (13/19 Pages) Texas Instruments – LOGARITHMIC AMPLIFIER

+
Input
A
−
+
Input
B
−
R
A1
Y
TL441
A2
R
Y
see
Note A
Z
B1
R
B2
Z
R
R
R
R
TL441ĆEP
LOGARITHMIC AMPLIFIER
SGLS268 − OCTOBER 2004
+
OUTPUT W
+
−
A1 _1/2 Y
(see Note B)
+
TL441
−
−
A2
Y
R
R
R
NOTES: A. Connections shown are for multiplication. For division, Z and Z connections are reversed.
B. Output W may need to be amplified to give actual product or quotient of A and B.
C. R designates resistors of equal value, typically 2 kΩ to 10 kΩ.
Multiplication: W = A • B ⇒ log W = log A + log B, or W = a(logaA ^{+ logaB)}
Division: W = A/B ⇒ log W = log A − log B, or W = a(logaA ^{+ logaB)}
Figure 15. Multiplication or Division
Input
A
+
−
R
nR
A1
Y
1/2
−
TL441
R
+
A2
Y
R
R
−
+
+
−
B1 _1/2 Z
B2 ^TL441 Z
Output
W
R
nR
R
NOTE: R designates resistors of equal value, typically 2 kΩ to 10 kΩ. The power to which the input variable is raised is fixed by setting nR.
Output W may need to be amplified to give the correct value.
Exponential: W = An ⇒ log W = n log A, or W = a(n ^{loga A)}
Figure 16. Raising a Variable to a Fixed Power
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