LM324, LM324A, LM224, LM2902, LM2902V
Figure 12. Function Generator
1
Vref = VCC
2
Vref
+
1/4
Figure 13. Multiple Feedback Bandpass Filter
VCC
C
Vin
R1
C
R3
–
LM324
+
Vref
1
Vref = 2 VCC
1/4
Triangle Wave
Output
R3
75 k
R1
100 k
Vref
Rf
f =
R1 + RC
4 CRf R1
if R3 =
R2 R1
R2 + R1
R2
300 k
+
1/4
LM324
–
CO
VO
CO = 10 C
LM324
–
C
Square
Wave
Output
R2
Given: fo = center frequency
A(fo) = gain at center frequency
Choose value fo, C
Then:
R3 =
R1 =
R2 =
Q
π
fo C
R3
2 A(fo)
R1 R3
2 R1 – R3
4Q
Qo fo
BW
< 0.1
For less than 10% error from operational amplifier,
where fo and BW are expressed in Hz.
If source impedance varies, filter may be preceded with
voltage follower buffer to stabilize filter parameters.
MOTOROLA ANALOG IC DEVICE DATA
7
MOTOROLA [ MOTOROLA, INC ]
