MAX7490 Maxim, MAX7490 Datasheet - Page 12

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

Dual Universal Switched-Capacitor Filters
Mode 2 Design Equations
Figure 5 shows the configuration of Mode 2N. This
mode extends the topology of Mode 3A to Mode 2,
where the highpass and lowpass outputs are summed
through two external resistors, R
lowpass notch filter that has higher frequency than the
one in Mode 2. Mode 2 is most useful in lowpass elliptic
designs. When cascading the sections of the
MAX7490/MAX7491, the highpass and lowpass outputs
can be summed directly into the inverting input of the
next section. Only one external op amp is needed.
12
Figure 5. Mode 2N, 2nd-Order Filter Providing a Lowpass Notch Output
f
f
Q
H
H
H
H
O
n
OLP
OBP
ON
ON
=
=
=
______________________________________________________________________________________
1
R
R
2
f
f
100
CLK
100
(
CLK
2
3
(
f
=
=
at f
→
−
−
1
R
R
R
R
+
1
0
=
1
2
3
Hz
1
f
R
R



CLK
+
V
4
2
R
)
IN
R
R
4
=
R
2
4
+
/ )
−
4
R
2
R
R
1
R1
2
2
=
COM






−
R
R
4
R
2
+
4
R
2
R4
R3
R2



H
and R
HP/N
L
+
, to create a
Σ
Mode 2N
S
-
C
C
∫
R
H
Mode 2N Design Equations
Figure 4. Mode 2, 2nd-Order Filter Providing a Highpass
Notch, Bandpass, and Lowpass Outputs
f
f
Q
H
O
n
BP
V IN
ON
=
=
=
∫
R
1
R
f
R1
f
CLK
100
(
CLK
100
3
2
f
COM
→
1
0
+
Hz
1
1
LP
R
R
+
+
R4
R3
R2
2
4
)
R
R
R
R
R
=
L
H
4
L
2
COM



R
R
G
H
HP/N
+
R
R
+
R
G
L
G
Σ



S
-



C
C
R
R
2
1



∫



LOWPASS
NOTCH
OUTPUT
R
4
R
+
4
R
BP
2



∫
LP