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RC4156/RC4157
PRODUCT SPECIFICATION
9
Figure 16. Bandpass Active Filter
These equations can be combined to obtain the transfer function:
and
65-0752
Set Center Frequency
C1
1000 pF
RC4156/57
B
V
BP
R2
R1
C2
1000 pF
RC4156/57
C
R6
100K
RC4156/57
A
R4
10K
R5
100K
R3
R7
V
Trim
Gain
and Q
IN
3
2
1
5
6
7
10
9
8
V
BP
s
( )
R1C1S
HP
s
( )
–
=
V
LP
s
( )
R2C2S
BP
s
( )
–
=
V
s
IN
s
( )
V
R3
R4
è
R1C1
×
S
2
R7
R6
R5
R4
R4
+
+
è
R1C1
S
R5
è
R1C1R2C2
è
+
+
------------------------------------------------------------R3
=
Defining 1/R1C1 as
w
1, 1/R2C2 as
w
2, and substituting in
the assigned values for R4, R5, and R6, then the transfer
function simplifies to:
This is now in a convenient form to look at the center-
frequency
w
0
and filter Q.
and
The frequency responses for various values of Q are shown
in Figure 17.
V
s
IN
s
( )
V
4
10
w
1
s
×
S
2
1.1
-------------R3
w
1
s
4
5
R7
10
+
1
10
+
w
1
w
2
----1
+
+
-----------------------R3
=
w
0
0.1
w
1
w
2
=
w
0
10
9
–
0.1R1R2
=
Q
1
5
4
R3
R7
+
1.1
10
+
----------------------
w
0
=
Figure 17. Bandpass Transfer Characteristics Normalized
for Unity Gain and Frequency
0
-10
-20
-30
-40
-50
-60
(
0.1
1.0
10
6
Q = 0.5
Q = 1.0
Q = 2.0
Q = 5.0
Q = 10
Q = 20
Q = 50
Q = 100
w
w
o
w
w
o
1
Q
V
V
=
1 -
+
2
2
2
w
w
o
1
Q
w
w
o