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