2 0 Modes of Operation
(Continued)
MODE 2 Notch 2 Bandpass Lowpass f
notch
k
f
O
(See
Figure 9
)
e
center frequency
f
O
f
f
R2
R2
e
CLK
a
1 or
CLK
a
1
100 R4
50
R4
f
CLK
f
CLK
or
f
notch
e
100
50
e
quality factor of the complex pole pair
Q
MODE 3 Highpass Bandpass Lowpass Outputs
(See
Figure 10
)
f
CLK
f
R2
R2
e
CLK
c
c
or
f
O
100
R4
50
R4
e
quality factor of the complex pole pair
Q
0
0
0
0
e
0
R2 R4
a
1
e
R2 R3
e
Lowpass output gain (as f
x
0)
H
OLP
R2 R1
e b
R2 R4
a
1
H
OBP
e
Bandpass output gain (at f
e
f
O
)
e b
R3 R1
H
ON1
e
Notch output gain (as f
x
0)
R2 R1
e b
R2 R4
a
1
f
CLK
e b
R2 R1
H
ON2
e
Notch output gain as f
x
2
Filter dynamics H
OBP
e
Q
0
H
OLP
H
ON2
e
0
H
ON1
H
ON2
H
OHP
e
Highpass Gain
H
OBP
e
H
OLP
e
J
H
R2
e
OHP
R4
H
OLP
e
0
H
OHP
c
H
OLP
c
Q
H
OBP
H
OLP(peak)
j
Q
c
H
OLP
(for high Q’s)
H
OHP(peak)
j
Q
c
H
OHP
(for high Q’s)
Circuit dynamics
J
Lowpass Gain at f
f
J
Lowpass Gain as f
x
0
J
as f
x
f
CLK
2
e
O
0
R4
R2
c
R3
R2
eb
R2
R1
eb
R3
R1
R4
eb
R1
TL H 10399 – 18
FIGURE 9 MODE 2
TL H 10399 – 19
In Mode 3 the feedback loop is closed around the input summing amplifier the finite GBW product of this op amp causes a slight Q enhancement If this is a
problem connect a small capacitor (10 pF
b
100 pF) across R4 to provide some phase lead
FIGURE 10 MODE 3
10
NSC [ NATIONAL SEMICONDUCTOR ]
