Rainbow Electronics MAX7480 - Manual (Page 8)

MAX7480
8th-Order, Lowpass, Butterworth,
Switched-Capacitor Filter
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Anti-Aliasing and Post-DAC Filtering
When using the MAX7480 for anti-aliasing or post-DAC
filtering, synchronize the DAC and the filter clocks. If
the clocks are not synchronized, beat frequencies 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 pass-
band. 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 MAX7480’s typical harmonic-distortion values with
a 10k
Ω
load at T A = +25°C.
V DD
V+ = +2.5V
V- = -2.5V
IN
CLK
GND
INPUT
OUTPUT OUT
0.1 µ F
CLOCK
*DRIVE SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
SHDN
COM
OS
0.1 µ F
MAX7480
*
V+
V-
Figure 4. Dual-Supply Operation
5th 3rd
-89 -68
-93 -73
200
100
f
CLK
(kHz)
4th 2nd
-85
-91
TYPICAL HARMONIC DISTORTION (dB)
-82
-89
4
2
1
MAX7480
V
IN
(Vp-p)
f
C
(kHz)
FILTER
400
200
f
IN
(Hz)
Table 1. Typical Harmonic Distortion
TRANSISTOR COUNT: 1116
Chip Information