MAX260BENG Maxim Integrated Products, MAX260BENG Datasheet - Page 22

• Manufacturer Part Number: MAX260BENG
• Description: Active Filter
• Manufacturer: Maxim Integrated Products

Specifications of MAX260BENG

• Number Of Channels: 2
• Cutoff Frequency: 7.5 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

errors are predictable, the graphs can be used to cor-
rect the selected f
parameters are on target. These predicted errors are
not unique to MAX260 series devices and, in fact,
occur with all types of sampled filters. Consequently,
these corrections can be applied to other switched
capacitor filters. In the majority of cases, the errors are
not significant, i.e., less than 1%, and correction is not
needed. However, the MAX262 does employ a lower
range of f
is more prone to sampling errors, as the tables show.
Maxim's filter design software applies the previous cor-
rections automatically as a function of desired f
and Q. Therefore, Figure 20 should not be used when
Maxim's software determines f
overcompensation of the sampling errors since the cor-
rection factors are then counted twice.
The data plotted in Figure 20 applies for modes 1 and
3. When using Figure 20 for mode 4, the f
obtained from the graph should be multiplied by 1.5
and the Q error should be multiplied by 3.0. In mode 2,
the value of f
programmed Q should be divided by √2 before using
the graphs.
As with all sampled systems, frequency components of
the input signal above one half the sampling rate are
aliased. In particular, input signal components near the
sampling rate generate difference frequencies that
often fall within the passband of the filter. Such aliased
signals, when they appear at the output, are indistin-
guishable from real input information. For example, the
aliased output signal generated when a 99kHz wave-
form is applied to a filter sampling at 100kHz (f
200kHz) is 1kHz. This waveform is an attenuated ver-
sion of the output that would result from a true 1kHz
input. Remember that, with the MAX260 series filters,
the nyquist rate (one half the sample rate) is in fact
f
A simple, passive RC lowpass input filter is usually suf-
ficient to remove input frequencies that can cause
aliasing. In many cases, the input signal itself may be
band limited and require no special anti-alias filtering.
The wideband MAX262 uses lower f
the MAX260/MAX261 and, for this reason, is more likely
to require input filtering than the MAX260 or MAX281.
The DC offset voltage at the LP or notch output can be
adjusted with the circuit in Figure 21. This circuit also
uses the input op amp to implement a single-pole anti-
alias filter. Note that the total offset is generally less in
multistage filters than when only one section is used,
Microprocessor Programmable
Universal Active Filters
22
CLK
/4, because f
______________________________________________________________________________________
CLK
CLK
/f
0
ratios than the MAX260 or MAX261 and
/f
CLK
0
0
should be multiplied by √2 and the
and Q so that the actual realized
is internally divided by two.
Trimming DC Offset
0
and Q. This results in
CLK
/f
0
ratios than
0
CLK
CLK
error
/f
0
=
,
Figure 17. MAX261 Bandpass Output Clock Noise
Figure 18. MAX260 Input Model
Figure 19. MAX261/MAX262 Input Model
500kHz TTL
TRACE A
V
IN
V
IN
f
CLK
~5pF
2
~5pF
IN
CLK
A
MAX261
f
A
CLK
2
R
BPA
IN
1µs/div
C
=
R
A
IN
C
12pF
IN
=
2
f
750 C
CLK
0.016pF
R, 10kΩ
12pF
2
C
A
C
IN
f
B
CLK
TRACE B
-
+
C, 1000pF
TRACE C
C
+
-
FB
C
FB
OV
OV
OV
A 1V/DIV
B 5mV/DIV
C mV/DIV