2 0 Modes of Operation
(Continued)
MODE 3a HP BP LP and Notch with External Op Amp
(See
Figure 11
)
f
CLK
f
R2
R2
e
CLK
c
c
or
f
O
100
R4
50
R4
R2 R3
e
c
Q
R4 R2
R2
H
OHP
e b
R1
0
0
0
MODE 4 Allpass Bandpass Lowpass Outputs
(See
Figure 12
)
e
center frequency
f
O
f
f
e
CLK
or
CLK
100
50
f
z
e
center frequency of the complex zero
Q
f
R3
e
O
e
BW
R2
Q
Z
e
quality factor of complex zero pair
e
For AP output make R1
e
R2
f
CLK
H
OAP
e
Allpass gain at 0
k
f
k
2
H
OLP
e
Lowpass gain (as f
x
0)
R2
eb
a
1
e b
2
R1
R3
R1
f
O
R3
R1
R4
H
OLP
e b
R1
H
OBP
e b
f
n
f
e
notch frequency
e
CLK
100
H
ON
e
gain of notch at
R
g
R
g
H
OLP
b
H
OHP
f
e
f
O
e
Q
R
I
R
h
R
g
c
H
OLP
H
n1
e
gain of notch (as f
x
0)
e
R
I
f
CLK
H
n2
e
gain of notch as f
x
2
R
g
c
H
OHP
eb
R
h
0
f
CLK
R
h
or
R
I
50
0
R
h
R
I
J
eb
R2
e b
1
R1
J
J
H
OBP
e
Bandpass gain (at f
e
f
O
)
R3
R2
R3
eb
eb
2
1
a
R2
R1
R2
Circuit Dynamics H
OBP
e
(H
OLP
)
c
Q
e
(H
OAP
a
1)Q
J
J
J
Due to the sampled data nature of the filter a slight mismatch of f
z
and f
O
occurs causing a 0 4 dB peaking around f
O
of the allpass filter amplitude
response (which theoretically should be a straight line) If this is unaccept-
able Mode 5 is recommended
TL H 10399 – 20
FIGURE 11 MODE 3a
TL H 10399 – 21
FIGURE 12 MODE 4
11
NSC [ NATIONAL SEMICONDUCTOR ]
