MAX261AENG Maxim Integrated Products, MAX261AENG Datasheet - Page 25

• Manufacturer Part Number: MAX261AENG
• Description: Active Filter
• Manufacturer: Maxim Integrated Products

Specifications of MAX261AENG

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

Figure 26 shows a fourth-order Butterworth lowpass
with a cutoff frequency of 3kHz. Sections A and B of a
MAX260 are cascaded. The f
each section are:
f
Q
Mode 1 and a 400kHz clock are used. Because of low
Q values, the sampling errors of Figure 20 begin to look
significant in this case. From the graphs, using f
ratio near 133, f
Q
are not a problem, the corrections can be ignored.
They are included here for best possible accuracy:
Figure 24. Wide Passband Chebyshev Bandpass Filter
0A
CLK
120kHz
A
A
= 3kHz
= 1.307
is -1.2% low, and Q
V
A,B
IN
MODE
-10
-30
-50
-70
Fourth-Order Butterworth Lowpass
10
CLK
CLK
IN
A
1
100
A
5
11
A
0
A is about 4% high, f
200
______________________________________________________________________________________
MODE
f
Q
CLK
BP
0B
2
B
A
B
1
12
500
FREQUENCY (Hz)
MAX260
= 3kHz
= 0.541
B
B
N = 56 N = 5 N = 96 N = 83
is -0.5% low. If these errors
1K
f
OA
IN
0
B
2K
23
and Q parameters for
PHASE
WR, AX, DX
PROGRAM
GAIN
f
OB
5K
0
BP
B is 1.5% high,
B
Q
Microprocessor Programmable
10K
21
A
-180
-90
0
90
180
V
OUT
Q
CLK
B
/f
0
Universal Active Filters
CLK
f
f
Q
Q
Measured wideband noise for this filter is 123µV RMS.
If mode 2 were used, the noise would be 87µV RMS.
For lower noise with either mode, the first section
should have the highest Q (section A in this example).
Figure 25. High-Frequency Chebyshev Bandpass Filter
CLK
CLK
1 to 3MHz
A
B
CLK
= 1.306 (N = 79, Q resolution prevents +0.5%
= 0.547 (N = 11 +1.1% correction)
A
/f
/f
0A
0B
= CLK
correction)
V
A,B
IN
= 135.08 (N = 22), f
= 139.80 (N = 25), f
-10
-20
-30
-40
-50
(-1.3% correction)
(-4.6% correction)
0
CLK
CLK
B
IN
MODE
1K
A
= 400kHz
A
5
11
1
f
f
O
CLK
= 15.6kHz
2K
= 1MHz
CLK
N = 38
BP
f
A
5K
FREQUENCY (Hz)
B
OA
1
12
MAX262
10K
0B
0A
f
f
O
CLK
f
f
O
CLK
= 47kHz
N = 0
= 31.3kHz
= 2961Hz
= 2861Hz
= 3MHz
f
IN
OB
20K
= 2MHz
B
23
WR, AX, DX
PROGRAM
50K
N = 96
Q
BP
A
100K
B
21
N = 96
V
Q
OUT
B
25