TL441CN Datasheet, PDF (13/20 Pages) Texas Instruments – LOGARITHMIC AMPLIFIER

+
Input
A
–
+
Input
B
–
APPLICATION INFORMATION
R
A1
Y
TL441
A2
R
Y
see
Note A
Z
B1
R
B2
Z
R
R
R
R
+
+
–
+
–
–
R
TL441
LOGARITHMIC AMPLIFIER
SLVS328 – OCTOBER 2000
A1 _1/2 Y
TL441
A2
Y
OUTPUT W
(see Note B)
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 16. Multiplication or Division
Input
A
+
–
R
nR
A1
Y
1/2
–
TL441
R
+
A2
Y
R
R
–
+
+
–
B1 _1/2 Z
TL441
B2
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 17. Raising a Variable to a Fixed Power
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
13