Datasheet MAX7426, MAX7427 Datasheet (MAXIM)

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General Description

The MAX7426/MAX7427 5th-order, lowpass, elliptic,
switched-capacitor filters (SCFs) operate from a single
+5V (MAX7426) or +3V (MAX7427) supply. The devices
draw only 0.8mA of supply current and allow corner fre­quencies from 1Hz to 12kHz, 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 MAX7426/MAX7427 deliver 37dB of stopband
rejection and a sharp rolloff with a transition ratio of

1.25. 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 12kHz)

♦ Single-Supply Operation

+5V (MAX7426)
+3V (MAX7427)

♦ Low Power

0.8mA (Operating Mode)

0.2µA (Shutdown Mode)

♦ Available in 8-Pin µMAX/PDIP Packages

♦ Low Output Offset: ±4mV

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

________________________________________________________________ Maxim Integrated Products 1

Typical Operating Circuit

19-1710; Rev 0; 4/00

Pin Configuration

Ordering Information

PART

MAX7426CUA

MAX7426CPA

MAX7426EUA -40°C to +85°C

0°C to +70°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

8 µMAX

8 Plastic DIP

8 µMAX

MAX7426EPA -40°C to +85°C 8 Plastic DIP

PART

TRANSITION RATIO

OPERATING

VOLTAGE (V)

MAX7426 r = 1.25 +5

Selector Guide

MAX7427 r = 1.25 +3

MAX7427CUA

MAX7427CPA

MAX7427EUA -40°C to +85°C

0°C to +70°C

0°C to +70°C 8 µMAX

8 Plastic DIP

8 µMAX

MAX7427EPA -40°C to +85°C 8 Plastic DIP

For free samples and the latest literature, visit www.maxim-ic.com or phone [phone].
For small orders, phone [phone].

87CLK

MAX7426
MAX7427

µMAX/PDIP

SHDNIN

OS

6

OUTV

5

0.1µF

INPUT

CLOCK

V

SUPPLY

V

DD

SHDN

IN

MAX7426
MAX7427

CLK

GND

OUT

COM

OUTPUT

OS

0.1µF

TOP VIEW

COM

GND

1

2

3

4

DD

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS—MAX7426

(VDD= +5V, filter output measured at OUT, 10kΩ

|| 50pF load to GND at OUT, SHDN = V

DD

, 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.......................................................1s

Continuous Power Dissipation (T

A

= +70°C)

8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW

8-Pin PDIP (derate 6.90mW/°C above +70°C).............552mW

Operating Temperature Ranges

MAX742 _C_A....................................................0°C to +70°C

MAX742 _E_A .................................................-40°C to +85°C

Storage Temperature Range .............................-65°C to +160°C

Lead Temperature (soldering, 10s) .................................+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

13.5 17.5 21.5f

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

90 130R

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 9f

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

±8 ±12.5I

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

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________ 3

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

ELECTRICAL CHARACTERISTICS—MAX7426 (continued)

(VDD= +5V, filter output measured at OUT, 10kΩ

|| 50pF load to GND at OUT, SHDN = V

DD

, 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—MAX7427

(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

0.8 1.0Supply 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

90 130R

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 12f

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

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters

4 _______________________________________________________________________________________

C

OSC

= 1000pF (Note 3)

CONDITIONS

13.5 17.5 21.5f

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

0.75 1.0

2.7 3.6V

DD

Supply Voltage

0.5V

IL

Clock Input Low

2.5V

IH

Clock Input High

±7.5 ±12.5I

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—MAX7427 (continued)

(VDD= +3V, filter output measured at OUT pin, 10kΩ

|| 50pF load to GND at OUT, SHDN = V

DD

, 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.)

ELLIPTIC FILTER CHARACTERISTICS (r = 1.25)

(VDD= +5V for MAX7426, VDD= +3V for MAX7427, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, SHDN = V

DD,

V

COM

= V

OS =VDD

/ 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 sinu-

soidal input at 0.2f

C

.

Note 2: DC insertion gain is defined as ∆V

OUT

/ ∆VIN.

Note 3: f

OSC

(kHz) ≈ 17.5 ✕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

mAI

DD

Supply Current

CLOCK

POWER REQUIREMENTS

SHUTDOWN

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________ 5

Typical Operating Characteristics

(VDD= +5V for MAX7426, VDD= +3V for MAX7427, f

CLK

= 100kHz, SHDN = VDD, V

COM

= VOS= VDD/ 2, TA= +25°C, unless other-

wise noted.)

-1.0

-0.6

-0.8

0

0.2

-0.2

-0.4

0.4

0 0.2 0.4 0.6 0.8 1.0

PASSBAND FREQUENCY RESPONSE

MAX7426/27-04

INPUT FREQUENCY (kHz)

GAIN (dB)

fC = 1kHz
r = 1.25

-400

-350

-250

-300

-200

-150

-100

-50

0

0 0.2 0.4 0.6 0.8 1.0 1.2

PHASE RESPONSE

MAX7426/27-06

INPUT FREQUENCY (kHz)

PHASE SHIFT (DEGREES)

fC = 1kHz
r = 1.25

0.70

0.74

0.72

0.78

0.76

0.80

0.82

2.5 3.5 4.03.0 4.5 5.0 5.5

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX7426/27-07

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

0.68

0.72

0.70

0.76

0.74

0.80

0.78

0.82

0.86

0.84

0.88

-60 -20 0-40 20 40 60 80 100

SUPPLY CURRENT vs. TEMPERATURE

MAX7426/27-08

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

VDD = +5V

VDD = +3V

FREQUENCY RESPONSE

10

0

-10

-20

-30

GAIN (dB)

-40

-50

-60

-70
012345

INPUT FREQUENCY (kHz)

fC = 1kHz
r = 1.25

MAX7426/27-02

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VDD= +5V for MAX7426, VDD= +3V for MAX7427, f

CLK

= 100kHz, SHDN = VDD, V

COM

= VOS= VDD/ 2, TA= +25°C, unless other-

wise noted.)

-90

-70

-80

-50

-60

-40

-30

-10

-20

0

012345

MAX7426

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. INPUT SIGNAL AMPLITUDE

MAX7426/27-10

AMPLITUDE (Vp-p)

THD + NOISE (dB)

A

B

SEE TABLE 1.

0 1.00.5 1.5 2.0 2.5 3.0

MAX7427

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. INPUT SIGNAL AMPLITUDE

MAX7426/27-12

AMPLITUDE (Vp-p)

THD + NOISE (dB)

-90

-70

-80

-50

-60

-40

-30

-10

-20

0

A

B

SEE TABLE 1.

Table 1. THD + Noise Test Conditions

LABEL

f

IN

(Hz)

f

C

(kHz)

A 200 1

B 1k 5

f

CLK

(kHz)

100

500

MEASUREMENT

BANDWIDTH (kHz)

22

80

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor

_______________________________________________________________________________________ 7

Typical Operating Characteristics (continued)

(VDD= +5V for MAX7426, VDD= +3V for MAX7427, f

CLK

= 100kHz, SHDN = VDD, V

COM

= VOS= VDD/ 2, TA= +25°C, unless other-

wise noted.)

0

50

100

150

200

0 1500 2000500 1000 2500 3000 3500

INTERNAL OSCILLATOR PERIOD

vs. SMALL CAPACITANCE (IN pF)

MAX7426/27-13

CAPACITANCE (pF)

OSCILLATOR PERIOD (µs)

VDD = +5V

VDD = +3V

INTERNAL OSCILLATOR FREQUENCY

vs. SUPPLY VOLTAGE

17.5

INTERNAL OSCILLATOR PERIOD

vs. LARGE CAPACITANCE (IN nF)

20

18

16

14

12

10

8

6

OSCILLATOR PERIOD (ms)

4

2

0

0 150 20050 100 250 300 350

VDD = +5V

VDD = +3V

CAPACITANCE (nF)

INTERNAL OSCILLATOR FREQUENCY

vs. TEMPERATURE

18.0

MAX7426/27-14

17.4

17.3

17.2

OSCILLATOR FREQUENCY (kHz)

C

= 1000pF

OSC

17.1

2.0 3.02.5 3.5 4.0 4.5 5.0 5.5
SUPPLY VOLTAGE (V)

DC OFFSET VOLTAGE

vs. TEMPERATURE

0

-0.5

-1.0

-1.5

-2.0

-2.5

DC OFFSET VOLTAGE (mV)

-3.0

-3.5

-40 0 20-20 40 60 80 100
TEMPERATURE (°C)

VDD = +3V

VDD = +5V

MAX7426/27-15

MAX7426/27-17

VDD = +5V

C

= 1000pF

OSC

VDD = +3V

TEMPERATURE (°C)

17.6

17.2

16.8

OSCILLATOR FREQUENCY (kHz)

16.4

16.0

-40 0 20-20 40 60 80 100

DC OFFSET VOLTAGE

vs. SUPPLY VOLTAGE

0

-0.5

-1.0

-1.5

-2.0

-2.5

DC OFFSET VOLTAGE (mV)

-3.0

-3.5

-4.0

2.5 3.53.0 4.0 4.5 5.0 5.5
SUPPLY VOLTAGE (V)

MAX7426/27-16

MAX7426/27-18

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters

8 _______________________________________________________________________________________

Detailed Description

The MAX7426/MAX7427 family of 5th-order, elliptic,
lowpass filters provides sharp rolloff with good stop­band rejection. All parts operate with a 100:1 clock-to­corner frequency ratio.

Most 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
MAX7426/MAX7427 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 MAX7426/MAX7427
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 allow 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 (Figure 2), 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, f

S

. 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 MAX7426/MAX7427 have a transition ratio of 1.25
and typically 37dB of stopband rejection.

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

Figure 1. 5th-Order Ladder Elliptic Filter Network

NAME FUNCTION

1 COM

Common Input Pin. Biased internally at midsupply. Bypass externally to GND with a 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 MAX7426 or +3V for MAX7427

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

C4C2

R

S

+

IN

-

L2

L4

C5C3C1V

R

L

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________ 9

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 MAX7426/MAX7427’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 MAX7426/MAX7427 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 midsupply 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

GAIN (dB)

Figure 2. Elliptic Filter Response

Figure 3. Offset Adjustment Circuit

RIPPLE

f

C

TRANSITION RATIO =

f

S

PASSBAND STOPBAND

f

CfS

f
f

FREQUENCY

V

SUPPLY

0.1µF

S
C

INPUT

CLOCK

IN

CLK

V

DD

MAX7426
MAX7427

GND

SHDN

OUT

COM

OUTPUT

0.1µF

OS

0.1µF

50k

50k

50k

f

CLK

f

=

C

100

f (kHz)

OSC

17.5 10

=

C (pF)

OSC

3

×

Z

=

IN

1

×

f C

CLK IN

VVVV

( )

=− +

OUT IN COM OS

V

V

COM

DD

2

typical

()

=

MAX7426/MAX7427

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 midsupply reduces the dynamic range.

Power Supplies

The MAX7426 operates from a single +5V supply, and
the MAX7427 operates 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. Single­supply 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 VDD. Use the MAX7427 for ±2.5, and use the
MAX7426 for ±1.5V. For ±5V dual-supply applications,
refer to 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 MAX7426/MAX7427 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 2 lists
typical harmonic distortion values with a 10kΩ load at
T

A

= +25°C.

Figure 4. Dual-Supply Operation

Table 2. Typical Harmonic Distortion

FILTER

f

IN

(Hz)

V

IN

(Vp-p)

2nd 4th

f

CLK

(kHz)

TYPICAL HARMONIC DISTORTION (dB)

3rd 5th

MAX7426

1k

200

4

500

100

-73-71

-88

1k

-90

-92

MAX7427

200

2

500

100

-87

-90

-90

-90

-82

-86

-86

-87

-88

-90

-90

TRANSISTOR COUNT: 1457
PROCESS: BiCMOS

Chip Information

V+

SHDN

COM

OS

*

OUTPUTOUT

0.1µF

V

DD

INPUT

V+

V-

*CONNECT SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.

CLOCK

IN

MAX7426
MAX7427

CLK

GND

V-

0.1µF

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

______________________________________________________________________________________ 11

________________________________________________________Package Information

8LUMAXD.EPS

MAX7426/MAX7427

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

© 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Package Information (continued)

PDIPN.EPS