MAX7490 Maxim, MAX7490 Datasheet - Page 11

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MAX7490

Manufacturer Part Number
MAX7490
Description
Dual Universal Switched-Capacitor Filters
Manufacturer
Maxim
Datasheet

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0
have to track Q). The notch and bandpass center fre-
quencies are identical. The notch output gain is the
same above and below the notch center frequency.
Mode 1 can also be used to make high-order Butter-
worth lowpass filters, low Q notches, and multiple-order
bandpass filters obtained by cascading identical
switched-capacitor sections.
Mode 1 Design Equations
Figure 3 shows the configuration of Mode 1B. R5 and
R6 are added to lower the feedback voltage from the
lowpass output to the summing input. This allows the
clock-to-center frequency to be adjusted beyond the
nominal value. This mode essentially has the same
functions and speed as Mode 1 while providing a high-
Q with f
Figure 2. Mode 1, 2nd-Order Filter Providing Notch, Bandpass,
and Lowpass Outputs
V
IN
R1
CLK
COM
/f
O
f
f
Q
H
H
H
H
O
notch
Dual Universal Switched-Capacitor Filters
ratios greater than the nominal value.
OLP
OBP
ON
ON
R3
R2
=
=
1
R
R
2
______________________________________________________________________________________
f
100
(
CLK
3
2
(
as f
=
at f
=
=
f
O
R
R
R
R
N
1
=
1
2
3
f
CLK
+
0
C
C
Hz
Σ
S
)
-
/ )
=
2
=
R
R
1
2
R
R
1
2
BP
Mode 1B
LP
Mode 1B Design Equations
Figure 4 shows the configuration of Mode 2. Mode 2 is
a combination of Mode 1 and Mode 3. In this mode,
f
However, it provides less sensitivity to resistor toler-
ances than does Mode 3. It has a highpass notch out-
put where the notch frequency depends solely on the
clock frequency.
Figure 3. Mode 1B, 2nd-Order Filter Providing Notch, Bandpass,
and Lowpass Outputs
CLK
V
IN
/f
O
R1
is always less than the part’s nominal ratio.
COM
f
f
Q
H
H
H
H
O
n
OLP
OBP
ON
ON
R3
R2
=
=
=
1
R
R
2
f
f
O
COM
100
(
CLK
3
2
(
as f
=
at f
=
R
R
R
R
R
N
1
=
R6
1
6
2
3
R
R
f
C
+
+
CLK
R
C
0
6
6
R
Hz
6
R
Σ
+
R
5
S
+
6
-
6
R
)
/ )
R
=
5
2
5
R5
=
R
R
1
2
R
R
1
2
BP
Mode 2
LP
11

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