Datasheet

MAX7401/MAX7405
8th-Order, Lowpass, Bessel,
Switched-Capacitor Filters
_______________________________________________________________________________________ 9
GND to the negative supply. Figure 4 shows an example
of dual-supply operation. Single- and dual-supply perfor-
mance are equivalent. For either single- or dual-supply
operation, drive CLK and SHDN from GND (V- in dual-
supply operation) to V
DD
. For ±5V dual-supply applica-
tions, use the MAX291–MAX297.
Input Signal Amplitude Range
The optimal input signal range is determined by observ-
ing the voltage level at which the total harmonic distor-
tion plus noise (THD+N) is minimized for a given corner
frequency. The Typical Operating Characteristics show
graphs of the devices’ THD+N response as the input
signal’s peak-to-peak amplitude is varied. These mea-
surements are made with OS and COM biased at mid-
supply.
Anti-Aliasing and Post-DAC Filtering
When using the MAX7401/MAX7405 for anti-aliasing or
post-DAC filtering, synchronize the DAC and the filter
clocks. If the clocks are not synchronized, beat frequen-
cies may alias into the passband.
The high clock-to-corner frequency ratio (100:1) also
eases the requirements of pre- and post-SCF filtering. At
the input, a lowpass filter prevents the aliasing of fre-
quencies around the clock frequency into the passband.
At the output, a lowpass filter attenuates the clock
feedthrough.
A high clock-to-corner frequency ratio allows a simple
RC lowpass filter, with the cutoff frequency set above
the SCF corner frequency, to provide input anti-aliasing
and reasonable output clock attenuation.
Harmonic Distortion
Harmonic distortion arises from nonlinearities within the
filter. These nonlinearities generate harmonics when a
pure sine wave is applied to the filter input. Table 1 lists
the MAX7401/MAX7405’s typical harmonic-distortion
values with a 10kΩ load at T
A
= +25°C.
V
DD
V+
V-
IN
CLK
GND
INPUT
OUTPUTOUT
0.1µF
CLOCK
*DRIVE SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
SHDN
COM
OS
0.1µF
MAX7401
MAX7405
*
V+
V-
Figure 4. Dual-Supply Operation
5th
3rd
-92-79
-93-83
500
100
f
CLK
(kHz)
4th
2nd
-92
-90
TYPICAL HARMONIC DISTORTION (dB)
-89
-91
4
5
1
MAX7401
V
IN
(Vp-p)
f
C
(kHz)
FILTER
1000
200
f
IN
(Hz)
Table 1. Typical Harmonic Distortion
TRANSISTOR COUNT: 1116
Chip Information
-88-82
-88-83
500
100
-88
-87
-83
-87
2
5
1
MAX7405
1000
200