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General Description
The MAX7408/MAX7411/MAX7412/MAX7415 5th-order,
lowpass, elliptic, switched-capacitor filters (SCFs) operate from a single +5V (MAX7408/MAX7411) or +3V
(MAX7412/MAX7415) supply. The devices draw only
1.2mA of supply current and allow corner frequencies
from 1Hz to 15kHz, making them ideal for low-power
post-DAC filtering and anti-aliasing applications. They
can be put into a low-power mode, reducing supply
current to 0.2µA.
Two clocking options are available: self-clocking (through
the use of an external capacitor) or external clocking for
tighter cutoff-frequency control. An offset-adjust pin
allows for adjustment of the DC output level.
The MAX7408/MAX7412 deliver 53dB of stopband
rejection and a sharp rolloff with a transition ratio of 1.6.
The MAX7411/MAX7415 achieve a sharper rolloff with a
transition ratio of 1.25 while still providing 37dB of stopband rejection. Their fixed response limits the design
task to selecting a clock frequency.
Applications
ADC Anti-Aliasing CT2 Base Stations
Post-DAC Filtering Speech Processing
Features
♦ 5th-Order, Elliptic Lowpass Filters
♦ Low Noise and Distortion: -80dB THD + Noise
♦ Clock-Tunable Corner Frequency (1Hz to 15kHz)
♦ Single-Supply Operation
+5V (MAX7408/MAX7411)
+3V (MAX7412/MAX7415)
♦ Low Power
1.2mA (operating mode)
0.2µA (shutdown mode)
♦ Available in 8-Pin µMAX/DIP Packages
♦ Low Output Offset: ±4mV
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
________________________________________________________________
Maxim Integrated Products
1
OS
OUTV
DD
1
2
87CLK
SHDNIN
GND
COM
µMAX/DIP
TOP VIEW
3
4
6
5
MAX7408
MAX7411
MAX7412
MAX7415
Typical Operating Circuit
19-1378; Rev 1; 10/98
Pin Configuration
Ordering Information
PART
MAX7408CPA
MAX7408CUA
MAX7408EPA -40°C to +85°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
8 Plastic DIP
8 µMAX
8 Plastic DIP
MAX7408EUA
MAX7415CPA
MAX7415CUA
MAX7415EPA -40°C to +85°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C 8 µMAX
8 Plastic DIP
8 µMAX
8 Plastic DIP
MAX7415EUA -40°C to +85°C 8 µMAX
PART
TRANSITION RATIO
OPERATING
VOLTAGE (V)
MAX7408 r = 1.6 +5
MAX7411 r = 1.25 +5
Selector Guide
MAX7412 r = 1.6 +3
MAX7415 r = 1.25 +3
MAX7411CPA
MAX7411CUA
MAX7411EPA -40°C to +85°C
0°C to +70°C
0°C to +70°C 8 Plastic DIP
8 µMAX
8 Plastic DIP
MAX7411EUA -40°C to +85°C 8 µMAX
MAX7412CPA
MAX7412CUA
MAX7412EPA -40°C to +85°C
0°C to +70°C
0°C to +70°C 8 Plastic DIP
8 µMAX
8 Plastic DIP
MAX7412EUA -40°C to +85°C 8 µMAX
V
SUPPLY
0.1µF
INPUT
CLOCK
IN
CLK
V
DD
MAX7408
MAX7411
MAX7412
MAX7415
GND
SHDN
OUT
COM
OUTPUT
OS
0.1µF
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS—MAX7408/MAX7411
(VDD= +5V; filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1µF from COM to GND,
f
CLK
= 100kHz, TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VDDto GND..............................................................-0.3V to +6V
IN, OUT, COM, OS, CLK, SHDN ................-0.3V to (V
DD
+ 0.3V)
OUT Short-Circuit Duration...................................................1sec
Continuous Power Dissipation (T
A
= +70°C)
8-Pin DIP (derate 6.90mW/°C above +70°C)...............552mW
8-Pin µMAX (derate 4.1mW/°C above +70°C).............330mW
Operating Temperature Ranges
MAX74_ _C_A.....................................................0°C to +70°C
MAX74_ _E_A ..................................................-40°C to +85°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
C
OSC
= 1000pF (Note 3)
VOS= 0 to V
DD
SHDN = GND, V
COM
= 0 to V
DD
(Note 1)
TA= +25°C
Input, COM externally driven
OS to OUT
Measured with respect to COM
fIN= 200Hz, VIN= 4Vp-p,
measurement bandwidth = 22kHz
VIN= V
COM
= V
DD
/ 2
V
COM
= V
DD
/ 2 (Note 2)
Output, COM internally driven
CONDITIONS
19 27 34f
OSC
Internal Oscillator Frequency
±0.2 ±10Input Leakage Current at OS
±0.2 ±10Input Leakage Current at COM
50 500C
L
10 1R
L
Resistive Output Load Drive
5Clock Feedthrough
110 180R
COM
Input Resistance at COM
±0.1V
OS
Input Voltage Range at OS
V
DD
- 0.2
V
DDVDD
+ 0.2
2 2 2
100:1f
CLK/fC
Clock-to-Corner Ratio
0.001 to 15f
C
Corner-Frequency Range
V
DD
- 0.5
V
DDVDD
+ 0.5
2 2 2
V
COM
COM Voltage Range
1A
OS
Offset Voltage Gain
-81THD+N
Total Harmonic Distortion plus
Noise
10Clock-to-Corner Tempco
0.25 VDD- 0.25Output Voltage Range
±4 ±25V
OFFSET
Output Offset Voltage
0 0.2 0.4
DC Insertion Gain with Output
Offset Removed
MIN TYP MAXSYMBOLPARAMETER
0.5V
IL
Clock Input Low
4.5V
IH
Clock Input High
±12 ±20I
CLK
Clock Output Current
(Internal Oscillator Mode)
V
V
µA
kHz
µA
µA
pF
kΩ
mVp-p
kΩ
V
V
V/V
dB
dB
mV
V
ppm/°C
kHz
UNITS
Maximum Capacitive Load
at OUT
FILTER
CLOCK
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
_______________________________________________________________________________________ 3
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
ELECTRICAL CHARACTERISTICS—MAX7408/MAX7411 (continued)
(VDD= +5V; filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1µF from COM to GND,
f
CLK
= 100kHz, TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.)
ELECTRICAL CHARACTERISTICS—MAX7412/MAX7415
(VDD= +3V, filter output measured at OUT pin, 10kΩ || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1µF from COM to
GND, f
CLK
= 100kHz; TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.)
CONDITIONS
MIN TYP MAXSYMBOLPARAMETER
Measured at DC
SHDN = GND
Operating mode, no load
0.5V
SDL
SHDN Input Low
4.5V
SDH
SHDN Input High
70PSRRPower-Supply Rejection Ratio
0.2 1I
SHDN
Shutdown Current
1.16 1.5Supply Current I
DD
4.5 5.5V
DD
Supply Voltage
V
V
dB
µA
mA
V
UNITS
SHDN Input Leakage Current
V
SHDN
= 0 to V
DD
±0.2 ±10 µA
V
OS
Input Voltage Range at OS
110 180R
COM
Input Resistance at COM kΩ
(Note 1)
TA= +25°C
Measured with respect to COM
OS to OUT
fIN= 200Hz, VIN= 2.5Vp-p,
measurement bandwidth = 22kHz
VIN= V
COM
= V
DD
/ 2
V
COM
= V
DD
/ 2 (Note 2)
CONDITIONS
50 500C
L
10 1R
L
Resistance Output Load Drive
3Clock Feedthrough
±0.1
V
DD
- 0.1
V
DDVDD
+ 0.1
2 2 2
V
COM
COM Voltage Range
100:1f
CLK
/
f
C
Clock-to-Corner Ratio
0.001 to 15f
C
Corner-Frequency Range
1A
OS
Offset Voltage Gain
-79THD+N
Total Harmonic Distortion plus
Noise
10Clock-to-Corner Tempco
0.25 VDD- 0.25Output Voltage Range
±4 ±25V
OFFSET
Output Offset Voltage
0 0.2 0.4
DC Insertion Gain with Output
Offset Removed
MIN TYP MAXSYMBOLPARAMETER
pF
kΩ
mVp-p
V
V
V/V
dB
dB
mV
V
ppm/°C
kHz
UNITS
Maximum Capacitive Load
at OUT
Input Leakage Current at COM
SHDN = GND, V
COM
= 0 to V
DD
±0.2 ±10 µA
Input Leakage Current at OS VOS= 0 to V
DD
±0.2 ±10 µA
POWER REQUIREMENTS
SHUTDOWN
FILTER CHARACTERISTICS
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
4 _______________________________________________________________________________________
C
OSC
= 1000pF (Note 3)
CONDITIONS
19 27 34f
OSC
Internal Oscillator Frequency
MIN TYP MAXSYMBOLPARAMETER
Measured at DC
SHDN = GND
Operating mode, no load
V
CLK
= 0 or 3V
0.5V
SDL
SHDN Input Low
2.5V
SDH
SHDN Input High
70PSRRPower-Supply Rejection Ratio
0.2 1I
SHDN
Shutdown Current
1.13 1.5
2.7 3.6V
DD
Supply Voltage
0.5V
IL
Clock Input Low
2.5V
IH
Clock Input High
±12 ±20I
CLK
Clock Output Current
(Internal Oscillator Mode)
V
V
dB
µA
V
V
V
µA
kHz
UNITS
SHDN Input Leakage Current
V
SHDN
= 0 to V
DD
±0.2 ±10 µA
ELECTRICAL CHARACTERISTICS—MAX7412/MAX7415 (continued)
(VDD= +3V, filter output measured at OUT pin, 10kΩ || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1µF from COM to
GND, f
CLK
= 100kHz; TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.)
mA
I
DD
Supply Current
ELLIPTIC FILTER (r = 1.6) CHARACTERISTICS—MAX7408/MAX7412
(VDD= +5V for MAX7408, VDD= +3V for MAX7412; filter output measured at OUT; 10kΩ || 50pF load to GND at OUT; SHDN = VDD;
V
COM
= V
OS
= V
DD
/ 2; f
CLK
= 100kHz; TA = T
MIN
to T
MAX
; unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)
f
IN
= 0.63f
C
fIN= 0.34f
C
fIN= 4.62f
C
fIN= 1.90f
C
fIN= 1.60f
C
fIN= 0.84f
C
fIN= 0.96f
C
fIN= f
C
CONDITIONS
-0.4 0.2 0.4
dB
-0.4 -0.2 0.4
Insertion Gain
with DC Gain Error Removed
(Note 4)
-53.4 -50
-53.4 -50
-53.4 -50
-0.4 -0.2 0.4
-0.4 0.2 0.4
-0.7 -0.2 0.2
UNITSMIN TYP MAXPARAMETER
CLOCK
POWER REQUIREMENTS
SHUTDOWN
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
_______________________________________________________________________________________ 5
ELLIPTIC FILTER (r = 1.25) CHARACTERISTICS—MAX7411/MAX7415
(VDD= +5V for MAX7411, VDD= +3V for MAX7415; filter output measured at OUT; 10kΩ || 50pF load to GND at OUT; SHDN = V
DD,
V
COM
= V
OS
= V
DD
/ 2; f
CLK
= 100kHz; TA = T
MIN
to T
MAX
; unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)
Note 1: The maximum f
C
is defined as the clock frequency f
CLK
= 100 · fCat which the peak SINAD drops to 68dB with a sinusoidal
input at 0.2f
C
.
Note 2: DC insertion gain is defined as ∆V
OUT
/ ∆VIN.
Note 3: f
OSC
(kHz) ≈ 27 · 103/ C
OSC(COSC
in pF).
Note 4: The input frequencies, f
IN
, are selected at the peaks and troughs of the ideal elliptic frequency responses.
f
IN
= 0.68f
C
fIN= 0.38f
C
fIN= 3.25f
C
fIN= 1.43f
C
fIN= 1.25f
C
fIN= 0.87f
C
fIN= 0.97f
C
fIN= f
C
CONDITIONS
-0.4 0.2 0.4
dB
-0.4 -0.2 0.4
Insertion Gain
with DC Gain Error Removed
(Note 4)
-37.2 -35
-37.2 -35
-38.5 -34
-0.4 -0.2 0.4
-0.4 0.2 0.4
-0.7 -0.2 0.2
UNITSMIN TYP MAXPARAMETER
-120
-100
-80
-20
0
-40
-60
20
0 1 2 3 4 5
MAX7408/MAX7412
FREQUENCY RESPONSE
MAX7408/11-01
INPUT FREQUENCY (kHz)
GAIN (dB)
fC = 1kHz
r = 1.6
-120
-100
-80
-20
0
-40
-60
20
0 1 2 3 4 5
MAX7411/MAX7415
FREQUENCY RESPONSE
MAX7408/11-02
INPUT FREQUENCY (kHz)
GAIN (dB)
fC = 1kHz
r = 1.25
-1.2
-1.0
-0.8
-0.2
0
-0.4
-0.6
0.2
0 204 408 612 816 1.02k
MAX7408/MAX7412
PASSBAND FREQUENCY RESPONSE
MAX7408/11-03
INPUT FREQUENCY (Hz)
GAIN (dB)
fC = 1kHz
r = 1.6
Typical Operating Characteristics
(VDD= +5V for MAX7408/MAX7411, VDD= +3V for MAX7412/MAX7415; f
CLK
= 100kHz; SHDN = VDD; V
COM
= VOS= VDD/ 2;
T
A
= +25°C; unless otherwise noted.)
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= +5V for MAX7408/MAX7411, VDD= +3V for MAX7412/MAX7415; f
CLK
= 100kHz; SHDN = VDD; V
COM
= VOS= VDD/ 2;
T
A
= +25°C; unless otherwise noted.)
-400
-350
-300
-250
-200
-150
-100
-50
0
0 0.40.2 0.6 0.8 1.0 1.2 1.4 1.6
MAX7408/MAX7412
PHASE RESPONSE
MAX7408/11-05
INPUT FREQUENCY (kHz)
PHASE SHIFT (DEGREES)
fC = 1kHz
r = 1.6
-600
-500
-400
-300
-200
-100
0
0 0.40.2 0.6 0.8 1.0 1.2 1.4 1.6
MAX7411/MAX7415
PHASE RESPONSE
MAX7408/11-06
INPUT FREQUENCY (kHz)
PHASE SHIFT (DEGREES)
fC = 1kHz
r = 1.25
-1.4
-1.0
-1.2
-0.8
-0.2
0
-0.4
-0.6
0.2
0 204 408 612 816 1.02k
MAX7411/MAX7415
PASSBAND FREQUENCY RESPONSE
MAX7408/11-04
INPUT FREQUENCY (Hz)
GAIN (dB)
fC = 1kHz
r = 1.25
1.11
1.13
1.12
1.15
1.14
1.16
1.17
2.5 3.5 4.03.0 4.5 5.0 5.5
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX7408/11-07
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
1.10
1.12
1.11
1.14
1.13
1.16
1.15
1.17
1.19
1.18
1.20
-60 -20 0-40 20 40 60 80 100
SUPPLY CURRENT vs. TEMPERATURE
MAX7408/11-08
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
VDD = +5V
VDD = +3V
-90
-70
-80
-50
-60
-40
-30
-10
-20
0
0 1 2 3 4 5
MAX7408
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT SIGNAL AMPLITUDE
MAX7408/11-09
AMPLITUDE (Vp-p)
THD + NOISE (dB)
B
A
SEE TABLE A
-90
-70
-80
-50
-60
-40
-30
-10
-20
0
0 1 2 3 4 5
MAX7411
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT SIGNAL AMPLITUDE
MAX7408/11-10
AMPLITUDE (Vp-p)
THD + NOISE (dB)
A
B
A
B
SEE TABLE A
LABEL
f
IN
(Hz)
f
C
(kHz)
A 200 1
B 1k 5
f
CLK
(kHz)
100
500
MEASUREMENT
BANDWIDTH (kHz)
22
80
Table A. THD + Noise Test Conditions
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass,
Elliptic, Switched-Capacitor
_______________________________________________________________________________________
7
0
40
20
80
60
100
120
0 1500 2000500 1000 2500 3000 3500
INTERNAL OSCILLATOR PERIOD
vs. SMALL CAPACITANCE (in pF)
MAX7408/11-13
CAPACITANCE (pF)
OSCILLATOR PERIOD (µs)
VDD = +5V
VDD = +3V
25.5
26.0
27.0
26.5
27.5
28.0
-50 -10 10-30 30 50 70 90 110
INTERNAL OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX7408/11-16
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
VDD = +3V
C
OSC
= 1000pF
VDD = +5V
0
4
2
8
6
10
12
0 150 20050 100 250 300 350
INTERNAL OSCILLATOR PERIOD
vs. LARGE CAPACITANCE (in nF)
MAX7408/11-14
CAPACITANCE (nF)
OSCILLATOR PERIOD (ms)
VDD = +5V
VDD = +3V
26.6
26.8
26.7
27.0
26.9
27.3
27.2
27.1
27.4
2.0 3.02.5 3.5 4.0 4.5 5.0 5.5
INTERNAL OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX7408/11-15
SUPPLY VOLTAGE
OSCILLATOR FREQUENCY (kHz)
C
OSC
= 1000pF
-3.5
-2.5
-3.0
-1.5
-2.0
-0.5
-1.0
0
-40 0 20-20 40 60 80 100
DC OFFSET VOLTAGE
vs. TEMPERATURE
MAX7408/11-17
TEMPERATURE (°C)
DC OFFSET VOLTAGE (mV)
VDD = +3V
VDD = +5V
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0
2.5 3.53.0 4.0 4.5 5.0 5.5
DC OFFSET VOLTAGE
vs. SUPPLY VOLTAGE
MAX7408/11-18
SUPPLY VOLTAGE (V)
DC OFFSET VOLTAGE (mV)
Typical Operating Characteristics (continued)
(VDD= +5V for MAX7408/MAX7411, VDD= +3V for MAX7412/MAX7415; f
CLK
= 100kHz; SHDN = VDD; V
COM
= VOS= VDD/ 2;
T
A
= +25°C; unless otherwise noted.)
-90
-70
-80
-50
-60
-40
-30
-10
-20
0
0 0.5 1.0 1.5 2.0 2.5 3.0
MAX7412
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT SIGNAL AMPLITUDE
MAX7408/11-11
AMPLITUDE (Vp-p)
THD + NOISE (dB)
B
A
SEE TABLE A
0 1.00.5 1.5 2.0 2.5 3.0
MAX7415
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT SIGNAL AMPLITUDE
MAX7408/11-12
AMPLITUDE (Vp-p)
THD + NOISE (dB)
-90
-70
-80
-50
-60
-40
-30
-10
-20
0
A
B
A
B
SEE TABLE A
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
8 _______________________________________________________________________________________
Detailed Description
The MAX7408/MAX7411/MAX7412/MAX7415 family of
5th-order, elliptic, lowpass filters provides sharp rolloff
with good stopband rejection. All parts operate with a
100:1 clock-to-corner frequency ratio and a 15kHz
maximum corner frequency.
Most switched-capacitor filters (SCFs) are designed
with biquadratic sections. Each section implements two
pole-zero pairs, and the sections can be cascaded to
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 MAX7408/MAX7411/
MAX7412/MAX7415 use an alternative approach, which
is to emulate a passive network using switched-capacitor integrators with summing 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 ladder elliptic filter structure.
A switched-capacitor filter that emulates a passive ladder filter retains many of the same advantages. The
component sensitivity of a passive ladder filter is low
when compared to a cascaded biquadratic design,
because each component affects the entire filter shape
rather than a single pole-zero pair. In other words, a
mismatched component in a biquadratic design has a
concentrated error on its respective poles, while the
same mismatch in a ladder filter design spreads its
error over all poles.
Elliptic Characteristics
Lowpass elliptic filters such as the MAX7408/MAX7411/
MAX7412/MAX7415 provide the steepest possible
rolloff with frequency of the four most common filter
types (Butterworth, Bessel, Chebyshev, and elliptic).
The high Q value of the poles near the passband edge
combined with the stopband zeros allows for the sharp
attenuation characteristic of elliptic filters, making these
devices ideal for anti-aliasing and post-DAC filtering in
single-supply systems (see the
Anti-Aliasing and Post-
DAC Filtering
section).
In the frequency domain, the first transmission zero
causes the filter’s amplitude to drop to a minimum level.
Beyond this zero, the response rises as the frequency
increases until the next transmission zero. The stopband begins at the stopband frequency, fS. At frequencies above fS, the filter’s gain does not exceed the gain
at fS. The corner frequency, fC, is defined as the point
where the filter output attenuation falls just below the
passband ripple. The transition ratio (r) is defined as
the ratio of the stopband frequency to the corner frequency:
r = fS / f
C
The MAX7408/MAX7412 have a translation ratio of 1.6
and typically 53dB of stopband rejection. The
MAX7411/MAX7415 have a transition ratio of 1.25 (providing a steeper rolloff) and typically 37dB of stopband
rejection.
C4C2
L4
C5C3C1V
IN
+
-
R
L
L2
R
S
Figure 1. 5th-Order Ladder Elliptic Filter Network
NAME FUNCTION
1 COM
Common Input Pin. Biased internally at mid-supply. Bypass externally to GND with 0.1µF capacitor. To
override internal biasing, drive with an external supply.
2 IN Filter Input
PIN
3 GND Ground
4 V
DD
Positive Supply Input, +5V for MAX7408/MAX7411 or +3V for MAX7412/MAX7415
8 CLK
Clock Input. Connect an external capacitor (C
OSC
) from CLK to GND to set the internal oscillator
frequency. To override the internal oscillator, connect to an external clock.
7
SHDN
Shutdown Input. Drive low to enable shutdown mode; drive high or connect to VDDfor normal operation.
6 OS
Offset Adjust Input. To adjust output offset, bias OS with a resistive voltage-divider between an external
supply and ground. Connect OS to COM if no offset adjustment is needed.
5 OUT Filter Output
Pin Description
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
_______________________________________________________________________________________ 9
Clock Signal
External Clock
These SCFs are designed for use with external clocks
that have a 40% to 60% duty cycle. When using an
external clock, drive the CLK pin with a CMOS gate
powered from 0 to VDD. Varying the rate of the external
clock adjusts the corner frequency of the filter:
Internal Clock
When using the internal oscillator, the capacitance
(C
OSC
) on CLK determines the oscillator frequency:
Since C
OSC
is in the low picofarads, minimize the stray
capacitance at CLK so that it does not affect the internal oscillator frequency. Varying the rate of the internal
oscillator adjusts the filter’s corner frequency by a
100:1 clock-to-corner frequency ratio. For example, an
internal oscillator frequency of 100kHz produces a
nominal corner frequency of 1kHz.
Input Impedance vs. Clock Frequencies
The MAX7408/MAX7411/MAX7412/MAX7415’s input
impedance is effectively that of a switched-capacitor
resistor (see the following equation), and is inversely
proportional to frequency. The input impedance values
determined by the equation represent the average input
impedance, since the input current is not continuous. As
a rule, use a driver with an output resistance less than
10% of the filter’s input impedance.
Estimate the input impedance of the filter by using the
following formula:
where f
CLK
= clock frequency and CIN= 1pF.
Low-Power Shutdown Mode
The MAX7408/MAX7411/MAX7412/MAX7415 have a
shutdown mode that is activated by driving SHDN low.
In shutdown mode, the filter supply current reduces to
0.2µA, and the output of the filter becomes high impedance. For normal operation, drive SHDN high or connect to VDD.
Applications Information
Offset (OS) and Common-Mode (COM)
Input Adjustment
COM sets the common-mode input voltage and is
biased at mid-supply with an internal resistor-divider. If
the application does not require offset adjustment, connect OS to COM. For applications where offset adjustment is required, apply an external bias voltage
through a resistor-divider network to OS, as shown in
Figure 3. For applications that require DC level shifting,
adjust OS with respect to COM. (Note: Do not leave OS
unconnected.) The output voltage is represented by
these equations:
where (VIN- V
COM
) is lowpass filtered by the SCF and
OS is added at the output stage. See the
Electrical
V V V V
V
V
typical
OUT IN COM OS
COM
DD
( )
( )
= − +
=
2
Z
1
(f C )
IN
CLK IN
=
⋅
f (kHz)
27 10
C (pF)
OSC
3
OSC
=
⋅
f
f
C
CLK
=
100
PASSBAND STOPBAND
GAIN (dB)
FREQUENCY
f
CfS
f
S
f
C
f
S
f
C
TRANSITION RATIO =
RIPPLE
Figure 2. Elliptic Filter Response
Figure 3. Offset Adjustment Circuit
V
SUPPLY
0.1µF
INPUT
CLOCK
IN
CLK
V
DD
MAX7408
MAX7411
MAX7412
MAX7415
GND
SHDN
OUT
COM
OUTPUT
0.1µF
OS
0.1µF
50k
50k
50k
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
10 ______________________________________________________________________________________
Characteristics
table for the input voltage range of COM
and OS. Changing the voltage on COM or OS significantly from mid-supply reduces the dynamic range.
Power Supplies
The MAX7408/MAX7411 operate from a single +5V
supply and the MAX7412/MAX7415 operate from a single +3V supply. Bypass VDDto GND with a 0.1µF
capacitor. If dual supplies are required, connect COM
to the system ground and GND to the negative supply.
Figure 4 shows an example of dual-supply operation.
Single-supply and dual-supply performance are equivalent. For either single-supply or dual-supply operation,
drive CLK and SHDN from GND (V- in dual supply
operation) to V
DD
. Use the MAX7408/MAX7411 for
±2.5, and use the MAX7412/MAX7415 for ±1.5V. For
±5V dual-supply applications, see the MAX291/
MAX292/MAX295/MAX296 and MAX293/MAX294/
MAX297 data sheets.
Input Signal Amplitude Range
The optimal input signal range is determined by observing the voltage level at which the signal-to-noise plus
distortion (SINAD) ratio is maximized for a given corner
frequency. The
Typical Operating Characteristics
show
the THD+Noise response as the input signal’s peak-topeak amplitude is varied.
Anti-Aliasing and Post-DAC Filtering
When using the MAX7408/MAX7411/MAX7412/
MAX7415 for anti-aliasing or post-DAC filtering, synchronize the DAC (or ADC) and the filter clocks. If the
clocks are not synchronized, beat frequencies may
alias into the desired passband.
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
typical harmonic distortion values with a 10kΩ load at
TA= +25°C.
V
DD
V+
V-
IN
CLK
GND
INPUT
OUTPUTOUT
0.1µF
CLOCK
*CONNECT SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
SHDN
COM
OS
0.1µF
MAX7408
MAX7411
MAX7412
MAX7415
*
V+
V-
Figure 4. Dual-Supply Operation
Table 1. Typical Harmonic Distortion
FILTER
f
IN
(Hz)
V
IN
(Vp-p)
MAX7408
1k
200
4
2nd 4th
f
CLK
(kHz)
500
100
-78.4-85.5
-88.2
TYPICAL HARMONIC DISTORTION (dB)
-92.8
-93
-86.9
-83.1 -89.5
3rd 5th
MAX7411
1k
200
4
500
100
-80-90
-88
1k
-92
-92
MAX7415
200
2
500
100
-87
-90
-90
-90
-88
-86
-86
-87
-88
-90
-90
MAX7412
1k
200
2
500
100
-93.1-86.6
-88.2
-90
-88.9
-85.6
-85.1 -85.7
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
______________________________________________________________________________________ 11
________________________________________________________Package Information
8LUMAXD.EPS
TRANSISTOR COUNT: 1457
Chip Information
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information (continued)
PDIPN.EPS
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