MAX7418 Maxim, MAX7418 Datasheet - Page 9

• Manufacturer Part Number: MAX7418
• Description: 5th-Order / Lowpass / Switched-Capacitor Filters
• Manufacturer: Maxim

The MAX7418/MAX7421/MAX7422/MAX7425 elliptic
lowpass filters provide sharp rolloff with good stopband
rejection. The MAX7419/MAX7423 Bessel filters provide
low overshoot and fast settling responses, and the
MAX7420/MAX7424 Butterworth filters provide a maxi-
mally flat passband response. All parts operate with a
100:1 clock-to-corner frequency ratio.
Most switch capacitor filters (SCFs) are designed with
biquadratic sections. Each section implements two
pole-zero pairs, and the sections can be cascaded to
_______________Detailed Description
(V
T
A
DD
PIN
= +25°C, unless otherwise noted.
1
2
3
4
5
6
7
8
= +5V for MAX7418–MAX7421, V
SHDN
NAME
COM
GND
OUT
CLK
V
OS
IN
DD
_______________________________________________________________________________________
3.0
2.5
2.0
1.5
1.0
0.5
0
Common Input Pin. Biased internally at midsupply. Bypass COM externally to GND with a 0.1µF capacitor.
To override internal biasing, drive COM with an external supply.
Filter Input
Ground
Positive Supply Input: +5V for MAX7418–MAX7421, +3V for MAX7422–MAX7425. Bypass V
a 0.1µF capacitor.
Filter Output
Offset Adjust Input. To adjust output offset, connect OS to an external supply through a resistive voltage-
divider (Figure 4). Connect OS to COM if no offset adjustment is needed. See the Offset and Common-Mode
Input Adjustment section.
Shutdown Input. Drive low to enable shutdown mode; drive high or connect to V
Clock Input. Connect an external capacitor (C
connect CLK to an external clock: f
-40
-15
DC OFFSET VOLTAGE
vs. TEMPERATURE
TEMPERATURE (°C)
10
DD
= +3V for MAX7422–MAX7425, f
V
35
DD
= 3V
V
Typical Operating Characteristics (continued)
DD
= 5V
60
85
Switched-Capacitor Filters
C
= f
CLK
/100.
OSC
produce higher order filters. The advantage to this
approach is ease of design. However, this type of
design is highly sensitive to component variations if any
section’s Q is high. The MAX7418–MAX7425 use an
alternative approach, which is to emulate a passive net-
work using switched-capacitor integrators with sum-
ming and scaling. The passive network may be
synthesized using CAD programs, or may be found in
many filter books. Figure 1 shows a basic 5th-order lad-
der filter structure.
FUNCTION
) from CLK to ground. To override the internal oscillator,
2.5
2.0
1.5
1.0
0.5
CLK
0
2.5
5th-Order, Lowpass,
= 2.2MHz, SHDN = V
3.0
vs. SUPPLY VOLTAGE
DC OFFSET VOLTAGE
SUPPLY VOLTAGE (V)
3.5
4.0
4.5
DD
DD
, V
5.0
Pin Description
COM
for normal operation.
5.5
= V
OS
DD
= V
to GND with
DD
/ 2,
9