MAX261BEWG Maxim Integrated Products, MAX261BEWG Datasheet - Page 23

• Manufacturer Part Number: MAX261BEWG
• Description: Active Filter
• Manufacturer: Maxim Integrated Products

Specifications of MAX261BEWG

• Number Of Channels: 2
• Cutoff Frequency: 57 KHz
• Supply Voltage (max): 12.6 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Operating Supply Voltage: 5 V
• Supply Voltage (min): 4.74 V
• Package / Case: SOIC-24 Wide
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

since each offset is typical negative and each section
inverts. When the HP or BP outputs are used, the offset
can be removed with capacitor coupling.
Figure 22 shows both halves of a MAX260 cascaded to
form a fourth-order Chebyshev bandpass filter. The
desired parameters are:
Center frequency (f
Pass bandwidth
Stop bandwidth
Max passband ripple
Min stopband attenuation
From the previous parameters, the order (number of
poles) and the f
mined. Such a derivation is beyond the scope of this
data sheet; however, there are a number of sources
that provide design data for this procedure. These
include look-up tables, design texts, and computer pro-
grams. Design software is available from Maxim to pro-
vide comprehensive solutions for most popular filter
configurations. The A and B section parameters for the
above filter are:
f
Q
To implement this filter, both halves operate in mode 1
and use the same clock. See Tables 2 and 3. The pro-
grammed parameters are:
CLK
f
f
1099.7Hz
Q
Sampling errors are very small at this f
the actual realized Q is very close to 7.05 (see Figure
20 or program MPP in the Filter Design Software sec-
tion). Often the realized Q is not exactly the target value
at high Qs because programming resolution lowers as
Q increases. This does not affect most filter designs,
since three-digit Q accuracy is practically never
required, and a Q resolution of 1 is provided up to Qs
of 10. The overall filter gain at f
(see the Cascading Filters section). If another gain is
required, amplification or attenuation must be added at
the input, output, or between stages.
CLK
0A
CLK
A
A
Fourth-Order Chebyshev Bandpass Filter
= 904Hz
= 7.05
= Q
A
/f
/f
0A =
= CLK
0B
B
= 7.11 (Mode 1, N = 119)
= 136.66 (Mode 1, N = 23), actual f
166.50 (Mode 1, N = 42), actual f
B
= 150kHz
0
and Q of each section can be deter-
______________________________________________________________________________________
0
f
Q
)
0B
B
= 1106Hz
= 7.05
Design Examples
= 15dB
= 1kHz
= 200Hz
= 600Hz
= 0.5dB
0
is 16.4V/V or 24.3dB
CLK
Microprocessor Programmable
0A
/f
= 902.4Hz
0
ratio, so
0B
=
Universal Active Filters
Figure 20. Sampling Errors in f
Q Settings
Figure 21. Circuit for DC Offset Adjustment
100kΩ
+5V
-5V
V
IN
20
18
16
14
12
10
-7
-6
-5
-4
-3
-2
-1
OFFSET
TRIM
8
6
4
2
0
0
NOTE: OP AMP INCLUDED WITH MAX261/MAX262
40
40
f
O
ERROR vs. f
f
MODE 2: MULTIPLY I
DIVIDE Q BY √2 BEFORE USING GRAPH
MODE 4: MUTIPLY f
Q ERROR IS PLOTTED FOR MODES 1 AND 3
MODE 2: MULTIPLY f
DIVIDE Q BY √2 BEFORE USING GRAPH
MODE 4: MUTIPLY Q ERROR BY 1.5
R
R
0
60
60
2
3
ERROR IS PLOTTED FOR MODES 1 AND 3
Q ERROR vs. f
100kΩ
270kΩ
Q = 0.512
Q = 0.5
80
80
Q = 0.6
Q = 0.512
Q = 0.83
Q = 0.512
100
100
CLK
f
f
CLK
CLK
CLK
Q = 0.512
Q = 1.21
/f
/f
/f
+
-
120 140 160 180 200
120 140 160 180 200
O
O
O
O
CLK
/f
CLK
RATIO
CLK/
RATIO
ERROR BY 1.5
RATIO (MODE 1, 3)
0
R
1
GAIN = -R
f
I
LP
O
/f
f
and Q at Low f
100kΩ
O
C
Q = 0.512
BY √2 and
O
Q = 3.05
=
BY √2 and
Q = 7.11
1
RATIO
Q = 0.512
2πR
1
1
/R
1
C
2
2
CLK
TO
FILTER
INPUT
/f
0
and
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