Datasheet
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
______________________________________________________________________________________ 19
H
OAP
= Allpass output gain for DC < f < f
CLK
/ 4
f
0
= ω
0
/ 2π
Filter Design Procedure
The procedure for most filter designs is to first convert
the required frequency response specifications to f
0
s
and Qs for the appropriate number of second-order
sections that implement the filter. This can be done by
using design equations or tables in available liter-
ature, or can be conveniently calculated using Maxim's
filter design software. Once the f
0
s and Qs have been
found, the next step is to turn them into the digital pro-
gram coefficients required by the MAX260/MAX261/
MAX262. An operating mode and clock frequency (or
clock/center frequency ratio) must also be selected.
Next, if the sample rate (f
CLK
/2) is low enough to cause
significant errors, the selected f
0
s and Qs should be
corrected to account for sampling effects by using
Figure 20 or Maxim's design software. In most cases,
the sampling errors are small enough to require no cor-
rection, i.e., less than 1%. In any case, with or without
correction, the required f
0
s and Qs can then be select-
ed from Tables 2 and 3. Maxim's filter design software
Gs H
s
sQ
ss Q
OAP
oo
oo
()
( / )
( / )
=
−+
++
2
2
2
2
ωω
ωω
f
P
f
C
H
OP
0.707 H
OLP
H
OLP
LOWPASS OUTPUT
f(LOG SCALE)
GAIN (V/V)
Figure 13. Second-Order Lowpass Characteristics
ffX
QQ
fp f
Q
HHX
Q
Q
CO
O
OP OLP
=
+
+
=
=
−−
−
−
1
1
2
1
1
2
1
1
1
2
1
1
1
1
4
22
2
2
2
f
C
f
P
H
OP
0.707 H
OHP
H
OHP
HIGHPASS OUTPUT
f(LOG SCALE)
GAIN (V/V)
Figure 14. Second-Order Highpass Characteristics
ffX
QQ
fp f
Q
HHX
Q
Q
CO
O
OP OHP
=
+
+
=
=
−−
−
−
1
1
2
1
1
2
1
1
1
2
1
1
1
1
4
22
2
2
2
f(LOG SCALE)
GAIN (V/V)
f
N
H
ON1
H
ON
H
ON2
Figure 15. Second-Order Notch Characteristics
TOTAL SECTIONS TOTAL B.W. TOTAL Q
1 1.000 B 1.00 Q
2 0.644 B 1.55 Q
3 0.510 B 1.96 Q
4 0.435 B 2.30 Q
5 0.386 B 2.60 Q
Table 6. Cascading Identical Bandpass
Filter Sections
Note: B = individual stage bandwidth, Q = individual
stage Q.