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General Description
The MAX7408/MAX7411/MAX7412/MAX7415 5th-order,
lowpass, elliptic, switched-capacitor filters (SCFs) oper-
ate 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 stop-
band 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
o5th-Order, Elliptic Lowpass Filters
oLow Noise and Distortion: -80dB THD + Noise
oClock-Tunable Corner Frequency (1Hz to 15kHz)
oSingle-Supply Operation
+5V (MAX7408/MAX7411)
+3V (MAX7412/MAX7415)
oLow Power
1.2mA (operating mode)
0.2µA (shutdown mode)
oAvailable in 8-Pin µMAX/DIP Packages
oLow Output Offset: ±4mV
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
________________________________________________________________
Maxim Integrated Products
1
OS
OUTVDD
1
2
8
7
CLK
SHDNIN
GND
COM
µMAX/DIP
TOP VIEW
3
4
6
5
MAX7408
MAX7411
MAX7412
MAX7415
VDD
IN
CLK
OUT
GND
INPUT
0.1µF
0.1µF
CLOCK
SHDN
OUTPUT
COM
OS
MAX7408
MAX7411
MAX7412
MAX7415
VSUPPLY
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
EVALUATION KIT
AVAILABLE
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,
fCLK = 100kHz, TA= TMIN to TMAX, 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.
VDD to GND..............................................................-0.3V to +6V
IN, OUT, COM, OS, CLK, SHDN ................-0.3V to (VDD + 0.3V)
OUT Short-Circuit Duration...................................................1sec
Continuous Power Dissipation (TA= +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
COSC = 1000pF (Note 3)
VOS = 0 to VDD
SHDN = GND, VCOM = 0 to VDD
(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 = VCOM = VDD / 2
VCOM = VDD / 2 (Note 2)
Output, COM internally driven
CONDITIONS
19 27 34fOSC
Internal Oscillator Frequency
±0.2 ±10Input Leakage Current at OS
±0.2 ±10Input Leakage Current at COM
50 500CL
10 1RL
Resistive Output Load Drive
5Clock Feedthrough
110 180RCOM
Input Resistance at COM
±0.1VOS
Input Voltage Range at OS
VDD - 0.2 VDD VDD + 0.2
2 2 2
100:1fCLK/fC
Clock-to-Corner Ratio
0.001 to 15fC
Corner-Frequency Range
VDD - 0.5 VDD VDD + 0.5
2 2 2
VCOM
COM Voltage Range
1AOS
Offset Voltage Gain
-81THD+N
Total Harmonic Distortion plus
Noise
10Clock-to-Corner Tempco
0.25 VDD - 0.25Output Voltage Range
±4 ±25VOFFSET
Output Offset Voltage
0 0.2 0.4
DC Insertion Gain with Output
Offset Removed
MIN TYP MAXSYMBOLPARAMETER
0.5VIL
Clock Input Low
4.5VIH
Clock Input High
±12 ±20ICLK
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
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
_______________________________________________________________________________________ 3
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,
fCLK = 100kHz, TA= TMIN to TMAX, 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, fCLK = 100kHz; TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
CONDITIONS MIN TYP MAXSYMBOLPARAMETER
Measured at DC
SHDN = GND
Operating mode, no load
0.5VSDL
SHDN Input Low
4.5VSDH
SHDN Input High
70PSRRPower-Supply Rejection Ratio
0.2 1ISHDN
Shutdown Current
1.16 1.5Supply Current IDD
4.5 5.5VDD
Supply Voltage
V
V
dB
µA
mA
V
UNITS
SHDN Input Leakage Current VSHDN = 0 to VDD ±0.2 ±10 µA
VOS
Input Voltage Range at OS
110 180RCOM
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 = VCOM = VDD / 2
VCOM = VDD / 2 (Note 2)
CONDITIONS
50 500CL
10 1RL
Resistance Output Load Drive
3Clock Feedthrough
±0.1
VDD - 0.1 VDD VDD + 0.1
2 2 2
VCOM
COM Voltage Range
100:1fCLK/fC
Clock-to-Corner Ratio
0.001 to 15fC
Corner-Frequency Range
1AOS
Offset Voltage Gain
-79THD+N
Total Harmonic Distortion plus
Noise
10Clock-to-Corner Tempco
0.25 VDD - 0.25Output Voltage Range
±4 ±25VOFFSET
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, VCOM = 0 to VDD ±0.2 ±10 µA
Input Leakage Current at OS VOS = 0 to VDD ±0.2 ±10 µA
POWER REQUIREMENTS
SHUTDOWN
FILTER CHARACTERISTICS
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
4 _______________________________________________________________________________________
COSC = 1000pF (Note 3)
CONDITIONS
19 27 34fOSC
Internal Oscillator Frequency
MIN TYP MAXSYMBOLPARAMETER
Measured at DC
SHDN = GND
Operating mode, no load
VCLK = 0 or 3V
0.5VSDL
SHDN Input Low
2.5VSDH
SHDN Input High
70PSRRPower-Supply Rejection Ratio
0.2 1ISHDN
Shutdown Current
1.13 1.5
2.7 3.6VDD
Supply Voltage
0.5VIL
Clock Input Low
2.5VIH
Clock Input High
±12 ±20ICLK
Clock Output Current
(Internal Oscillator Mode)
V
V
dB
µA
V
V
V
µA
kHz
UNITS
SHDN Input Leakage Current VSHDN = 0 to VDD ±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, fCLK = 100kHz; TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
mA
IDD
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;
VCOM = VOS =V
DD / 2; fCLK = 100kHz; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)
fIN = 0.63fC
fIN = 0.34fC
fIN = 4.62fC
fIN = 1.90fC
fIN = 1.60fC
fIN = 0.84fC
fIN = 0.96fC
fIN = fC
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 = VDD,
VCOM = VOS =V
DD / 2; fCLK = 100kHz; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)
Note 1: The maximum fCis defined as the clock frequency fCLK = 100 ·fCat which the peak SINAD drops to 68dB with a sinusoidal
input at 0.2fC.
Note 2: DC insertion gain is defined as ∆VOUT / ∆VIN.
Note 3: fOSC (kHz) ≈ 27 ·103/ COSC (COSC in pF).
Note 4: The input frequencies, fIN, are selected at the peaks and troughs of the ideal elliptic frequency responses.
fIN = 0.68fC
fIN = 0.38fC
fIN = 3.25fC
fIN = 1.43fC
fIN = 1.25fC
fIN = 0.87fC
fIN = 0.97fC
fIN = fC
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
012345
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
012345
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; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2;
TA= +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; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2;
TA= +25°C; unless otherwise noted.)
-400
-350
-300
-250
-200
-150
-100
-50
0
00.40.2 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
00.40.2 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
012345
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
012345
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 fIN
(Hz)
fC
(kHz)
A200 1
B1k 5
fCLK
(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 30507090110
INTERNAL OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX7408/11-16
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
VDD = +3V
COSC = 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)
COSC = 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; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2;
TA= +25°C; unless otherwise noted.)
01.00.5 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-capaci-
tor 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 lad-
der 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 stop-
band begins at the stopband frequency, fS. At frequen-
cies 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 fre-
quency:
r = fS / fC
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 (pro-
viding a steeper rolloff) and typically 37dB of stopband
rejection.
C4C2
L4
C5C3C1VIN
+
-RL
L2
RS
Figure 1. 5th-Order Ladder Elliptic Filter Network
NAME FUNCTION
1COM 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.
2IN Filter Input
PIN
3GND Ground
4 VDD Positive Supply Input, +5V for MAX7408/MAX7411 or +3V for MAX7412/MAX7415
8CLK Clock Input. Connect an external capacitor (COSC) from CLK to GND to set the internal oscillator
frequency. To override the internal oscillator, connect to an external clock.
7SHDN Shutdown Input. Drive low to enable shutdown mode; drive high or connect to VDD for normal operation.
6OS 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.
5OUT 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
(COSC) on CLK determines the oscillator frequency:
Since COSC is in the low picofarads, minimize the stray
capacitance at CLK so that it does not affect the inter-
nal 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 fCLK = 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 imped-
ance. For normal operation, drive SHDN high or con-
nect 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, con-
nect OS to COM. For applications where offset adjust-
ment 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 - VCOM) is lowpass filtered by the SCF and
OS is added at the output stage. See the
Electrical
VVVV
VVtypical
OUT IN COM OS
COM DD
( )
()
=− +
=2
Z 1
(f C )
IN CLK IN
=×
f
OSC(kHz) k
COSC(pF)
=
ff
CCLK
=100
PASSBAND STOPBAND
GAIN (dB)
FREQUENCY
fCfS
fS
fCfS
fC
TRANSITION RATIO =
RIPPLE
VDD
VSUPPLY
IN
CLK
GND
INPUT
OUTPUT
50k
50k
50k
OUT
0.1µF
0.1µF
0.1µF
CLOCK
SHDN
COM
OS
MAX7408
MAX7411
MAX7412
MAX7415
Figure 2. Elliptic Filter Response Figure 3. Offset Adjustment Circuit
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 signifi-
cantly 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 sin-
gle +3V supply. Bypass VDD to GND with a 0.1µF
capacitor. If dual supplies are required, connect COM
to the system ground and GND to the negative supply.
Figure 5 shows an example of dual-supply operation.
Single-supply and dual-supply performance are equiv-
alent. For either single-supply or dual-supply operation,
drive CLK and SHDN from GND (V- in dual supply
operation) to VDD. 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 observ-
ing 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-to-
peak amplitude is varied.
Anti-Aliasing and Post-DAC Filtering
When using the MAX7408/MAX7411/MAX7412/
MAX7415 for anti-aliasing or post-DAC filtering, syn-
chronize 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 10kΩload at
TA= +25°C.
VDD
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 5. Dual-Supply Operation
Table 1. Typical Harmonic Distortion
FILTER fIN
(Hz)
VIN
(Vp-p)
MAX7408 1k
200 4
2nd 4th
fCLK
(kHz)
500
100
TBDTBD
TBD
TYPICAL HARMONIC DISTORTION (dB)
TBD
TBD
TBD
TBD TBD
3rd 5th
MAX7411 1k
200 4
500
100
TBDTBD
TBD
1k
TBD
TBD
MAX7415 200 2
500
100
TBD
TBD
TBD
TBD
TBD
TBD
TBD
TBD
TBD
TBD
TBD
MAX7412 1k
200 2
500
100
TBDTBD
TBD
TBD
TBD
TBD
TBD TBD
MAX7408/MAX7411/MAX7412/MAX7415
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
______________________________________________________________________________________ 11
________________________________________________________Package Information
α
α
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
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© 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information (continued)
PDIPN.EPS