MF10 Datasheet, PDF (11/20 Pages) National Semiconductor (TI) – Universal Monolithic Dual Switched Capacitor Filter

2 0 Modes of Operation (Continued)
MODE 3a HP BP LP and Notch with External Op Amp
(See Figure 11 )
f_O
0 0 ^{e fCLK c}
R2
or
f_CLK
c
R2
100
R4 50
R4
Q
0^{R2 R3}
e
c
R4 R2
R2
H_OHP
e
b
R1
R3
H_OBP
e
b
R1
R4
H_OLP
e
b
R1
f_n
0 0 ^{e notch frequency e fCLK Rh or fCLK Rh}
100 R_I
50 R_I
H_ON e gain of notch at
 J ^{f e fO e}
Q
R_g
R_I
H_OLP
b
R_g
R_h
H_OHP
x H_n1 e gain of notch (as f
0)
e
R_g
R_I
c
H_OLP
 J ^{x Hn2 e gain of notch as f}
f_CLK
2
e
b^Rg
R_h
c
H_OHP
MODE 4 Allpass Bandpass Lowpass Outputs
(See Figure 12 )
f_O e center frequency
e ^fCLK or ^fCLK
100 50
f_z e center frequency of the complex zero f_O
Q
e
f_O
R3
e
BW R2
R3
Q_Z
e
quality
factor
of
complex
zero
pair
e
R1
For AP output make R1 e R2
 J ^{HOAP e Allpass gain}
at 0 ^k f ^{k fCLK}
2
R2
e b e b1
R1
x H_OLP e Lowpass gain (as f
0)
 J ^R2
eb
a 1 e b2
R1
H_OBP e Bandpass gain (at f e f_O)
 J  J ^R3
R2
R3
eb
1a
eb2
R2
R1
R2
Circuit Dynamics H_OBP e (H_OLP) c Q e (H_OAP a 1)Q
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
FIGURE 11 MODE 3a
TL H 10399 – 20
FIGURE 12 MODE 4
11
TL H 10399 – 21