Datasheet MAX7401ESA, MAX7401EPA, MAX7401CPA, MAX7401CSA, MAX7405ESA Datasheet (Maxim)

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone].

General Description

The MAX7401/MAX7405 8th-order, lowpass, Bessel,
switched-capacitor filters (SCFs) operate from a single
+5V (MAX7401) or +3V (MAX7405) supply. These
devices draw only 2mA of supply current and allow cor­ner frequencies from 1Hz to 5kHz, making them ideal
for low-power post-DAC filtering and anti-aliasing appli­cations. They feature a shutdown mode that reduces
supply current to 0.2µA.

Two clocking options are available on these devices:
self-clocking (through the use of an external capacitor)
or external clocking for tighter corner-frequency control.
An offset adjust pin allows for adjustment of the DC out­put level.

The MAX7401/MAX7405 Bessel filters provide low over­shoot and fast settling. Their fixed response simplifies
the design task to selecting a clock frequency.

Applications

ADC Anti-Aliasing CT2 Base Stations
Post-DAC Filtering Speech Processing
Air-Bag Electronics

Features

♦ 8th-Order, Lowpass Bessel Filters
♦ Low Noise and Distortion: -82dB THD + Noise
♦ Clock-Tunable Corner Frequency (1Hz to 5kHz)
♦ 100:1 Clock-to-Corner Ratio
♦ Single-Supply Operation

+5V (MAX7401)
+3V (MAX7405)

♦ Low Power

2mA (Operating Mode)

0.2µA (Shutdown Mode)

♦ Available in 8-Pin SO/DIP Packages
♦ Low Output Offset: ±5mV

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,

Switched-Capacitor Filters

________________________________________________________________

Maxim Integrated Products

1

OS

OUTV

DD

1
2

87CLK

SHDNIN

GND

COM

SO/DIP

TOP VIEW

3

4

6

5

MAX7401
MAX7405

V

DD

IN

CLK

OUT

GND

INPUT

0.1µF

0.1µF

CLOCK

SHDN

OUTPUT

V

SUPPLY

COM

OS

MAX7401
MAX7405

Typical Operating Circuit

19-4788; Rev 1; 6/99

Pin Configuration

Ordering Information

PART

MAX7401CPA
MAX7401ESA
MAX7401EPA -40°C to +85°C

-40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

8 Plastic DIP
8 SO

8 Plastic DIP
MAX7405CSA
MAX7405CPA
MAX7405ESA
MAX7405EPA -40°C to +85°C

-40°C to +85°C

0°C to +70°C

0°C to +70°C 8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

MAX7401CSA

0°C to +70°C 8 SO

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,
Switched-Capacitor Filters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS—MAX7401

(VDD= +5V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF from COM to GND,

SHDN = VDD, 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

MAX7401..............................................................-0.3V to +6V

MAX7405..............................................................-0.3V to +4V

IN, OUT, COM, OS, CLK ...........................-0.3V to (V

DD

+ 0.3V)

SHDN........................................................................-0.3V to +6V

OUT Short-Circuit Duration...................................................1sec

Continuous Power Dissipation (T

A

= +70°C)

8-Pin SO (derate 5.88mW/°C above +70°C)................471mW

8-Pin DIP (derate 9.09mW/°C above +70°C)...............727mW

Operating Temperature Ranges

MAX740 _C_A ....................................................0°C to +70°C

MAX740 _E_A .................................................-40°C to +85°C

Storage Temperature Range.............................-65°C to +150°C

Lead Temperature (soldering, 10sec).............................+300°C

C

OSC

= 1000pF (Note 4)

VOS= 0 to (VDD- 1V) (Note 3)

SHDN = GND, V

COM

= 0 to V

DD

(Note 1)

Input, COM externally driven

fIN= 200Hz, VIN= 4Vp-p,
measurement bandwidth = 22kHz

VIN= V

COM

= V

DD

/ 2

V

COM

= V

DD

/ 2 (Note 2)

CONDITIONS

29 38 48f

OSC

Internal Oscillator Frequency

±0.1 ±10Input Leakage Current at OS

±0.1 ±10Input Leakage Current at COM

50 500C

L

10 1R

L

Resistive Output Load Drive

10Clock Feedthrough

75 125R

COM

Input Resistance at COM

100:1f

CLK

/f

C

Clock-to-Corner Ratio

0.001 to 5f

C

Corner Frequency

V

COM

1A

OS

OS Voltage Gain to OUT

-82THD+N

Total Harmonic Distortion
plus Noise

10Clock-to-Corner Tempco

0.25 V

DD

-

0.25Output Voltage Range

±5 ±25V

OFFSET

Output Offset Voltage

-0.1 0.15 0.3

DC Insertion Gain with
Output Offset Removed

MIN TYP MAX

SYMBOLPARAMETER

V

CLK

= 0 or 5V

0.5V

IL

Clock Input Low

V

DD

- 0.5V

IH

Clock Input High

±15 ±30I

CLK

Clock Input Current

V

V

µA

kHz

µA

µA

pF

kΩ

mVp-p

kΩ

V

V/V

dB

dB

mV

V

ppm/°C

kHz

UNITS

Maximum Capacitive Load at
OUT

COM Voltage Range

V

DD

/ 2

V

DD

/ 2

V

DD

/ 2

- 0.5 + 0.5

V

COM

±0.1V

OS

Input Voltage Range at OS V

V

DD

/ 2

V

DD

/ 2

V

DD

/ 2

- 0.2 + 0.2

FILTER CHARACTERISTICS

CLOCK

Output, COM internally biased

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,

Switched-Capacitor Filters

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS—MAX7401 (continued)

(VDD= +5V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF from COM to GND,
SHDN = V

DD

, f

CLK

= 100kHz, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS—MAX7405

(VDD= +3V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF from COM to GND,
SHDN = V

DD

, f

CLK

= 100kHz, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

CONDITIONS

MIN TYP MAX

SYMBOLPARAMETER

Measured at DC

SHDN = GND, CLK driven from 0 to V

DD

Operating mode, no load, IN = OS = COM

0.5V

SDL

SHDN Input Low

V

DD

- 0.5V

SDH

SHDN Input High

60PSRRPower-Supply Rejection Ratio

0.2 1I

SHDN

Shutdown Current

2 3.5Supply 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

±0.1 ±10 µA

POWER REQUIREMENTS

SHUTDOWN

µA±0.1 ±10VOS= 0 to (V

DD

- 1V) (Note 3)Input Leakage Current at OS

µA±0.1 ±10

SHDN = GND, V

COM

= 0 to V

DD

Input Leakage Current at COM

Maximum Capacitive
Load at OUT

UNITS

kHz

ppm/°C

V

mV
dB

dB

V/V

V

mVp-p

kΩ

pF

PARAMETER SYMBOL

MIN TYP MAX

DC Insertion Gain with
Output Offset Removed

-0.1 0.03 0.3

Output Offset Voltage V

OFFSET

±5 ±25

Output Voltage Range 0.25 V

DD

-

0.25

Clock-to-Corner Tempco 10

Total Harmonic Distortion
plus Noise

THD+N -84

OS Voltage Gain to OUT A

OS

1

Corner Frequency f

C

0.001 to 5

Clock-to-Corner Ratio f

CLK

/

f

C

100:1

COM Voltage Range V

COM

V

DD

/ 2

V

DD

/ 2

V

DD

/ 2

- 0.1 + 0.1

Clock Feedthrough 10
Resistance Output Load Drive R

L

10 1

C

L

50 500

CONDITIONS

V

COM

= V

DD

/ 2 (Note 2)

VIN= V

COM

= V

DD

/ 2

fIN= 200Hz, VIN= 2.5Vp-p,
measurement bandwidth = 22kHz

(Note 1)

kΩInput Resistance at COM R

COM

75 125

COM internally biased or externally driven

VInput Voltage Range at OS V

OS

V

COM

±0.1

FILTER CHARACTERISTICS

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,
Switched-Capacitor Filters

4 _______________________________________________________________________________________

C

OSC

= 1000pF (Note 4)

CONDITIONS

26 34 43f

OSC

Internal Oscillator Frequency

MIN TYP MAX

SYMBOLPARAMETER

Measured at DC

SHDN = GND, CLK driven from 0 to V

DD

Operating mode, no load, IN = OS = COM

V

CLK

= 0 or 3V

0.5V

SDL

SHDN Input Low

V

DD

- 0.5V

SDH

SHDN Input High

60PSRRPower-Supply Rejection Ratio

0.2 1I

SHDN

Shutdown Current

2 3.5

2.7 3.6V

DD

Supply Voltage

0.5V

IL

Clock Input Low

V

DD

- 0.5V

IH

Clock Input High

±15 ±30I

CLK

Clock Input Current

V

V

dB

µA

V

V

V

µA

kHz

UNITS

SHDN Input Leakage Current

V

SHDN

= 0 to V

DD

±0.1 ±10 µA

FILTER CHARACTERISTICS—MAX7401/MAX7405

(VDD= +5V for MAX7401, VDD= +3V for MAX7405; filter output measured at OUT; 10kΩ || 50pF load to GND at OUT; SHDN = VDD;
V

COM = VOS = VDD

/2; f

CLK

= 100kHz; TA = T

MIN

to T

MAX

; unless otherwise noted. Typical values are at TA= +25°C.)

Note 1: The maximum f

C

is defined as the clock frequency, f

CLK

= 100 · fC,at 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: OS voltages above V

DD

- 1V saturate the input and result in a 75µA typical input leakage current.

Note 4: For MAX7401, f

OSC

(kHz) ≅ 38 · 103/ C

OSC

(pF). For MAX7405, f

OSC

(kHz) ≅ 34 · 103/ C

OSC

(pF).

CLOCK

POWER REQUIREMENTS

SHUTDOWN

CONDITIONS UNITS

MIN TYP MAX

PARAMETER

mAI

DD

Supply Current

ELECTRICAL CHARACTERISTICS—MAX7405 (continued)

(VDD= +3V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF from COM to GND,
SHDN = V

DD

, f

CLK

= 100kHz, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

fIN= 0.5f

C

-1.0 -0.8 -0.6

fIN= f

C

-3.3 -3.0 -2.7

fIN= 3f

C

-33 -29

fIN= 6f

C

dB

-79 -74

Insertion Gain Relative to
DC Gain

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,

Switched-Capacitor Filters

_______________________________________________________________________________________ 5

-70

-50

-60

-40

-10

0

-20

-30

10

012345

FREQUENCY RESPONSE

MAX7401 toc01

INPUT FREQUENCY (kHz)

GAIN (dB)

fC = 1kHz

-3.5

-2.5

-3.0

-2.0

-0.5

0

-1.0

-1.5

0.5

0 202 404 606 808 1010

PASSBAND FREQUENCY RESPONSE

MAX7409 toc02

INPUT FREQUENCY (Hz)

GAIN (dB)

fC = 1kHz

1.97

1.99

1.98

2.01

2.00

2.02

2.03

-40 20 40-20 0 60 80 100

SUPPLY CURRENT

vs. TEMPERATURE

MAX7401 toc05

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

NO LOAD

MAX7401

MAX7405

10,000

0.1

0.01 0.1 1 10 100 1000

INTERNAL OSCILLATOR FREQUENCY

vs. C

OSC

CAPACITANCE

1

MAX7401 toc08

C

OSC

CAPACITANCE (nF)

OSCILLATOR FREQUENCY (kHz)

10

100

1000

-20

-15

-10

-5

0

5

10

15

20

2.5 3.53.0 4.0 4.5 5.0 5.5

OFFSET VOLTAGE

vs. SUPPLY VOLTAGE

MAX7401 toc06

SUPPLY VOLTAGE (V)

OFFSET VOLTAGE (mV)

MAX7401

VIN = V

COM

= V

DD

/ 2

MAX7405

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

2.5 3.53.0 4.0 4.5 5.0 5.5

NORMALIZED OSCILLATOR FREQUENCY

vs. SUPPLY VOLTAGE

MAX7401 toc09

SUPPLY VOLTAGE (V)

NORMALIZED OSCILLATOR FREQUENCY

C

OSC

= 390pF

MAX7401

MAX7405

-400

-300

-350

-250

-100

-50

-150

-200

0

0 400 800 1200 1600 2000

PHASE RESPONSE

MAX7401 toc03

INPUT FREQUENCY (Hz)

PHASE SHIFT (DEGREES)

fC = 1kHz

1.5

1.8

1.7

1.6

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.5 3.53.0 4.0 4.5 5.0 5.5

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX7401 toc04

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

NO LOAD

MAX7405

MAX7401

-1.5

-1.0

0

-0.5

0.5

1.0

-40 0-20 20 40 60 80 100

OFFSET VOLTAGE vs. TEMPERATURE

MAX7401 toc07

TEMPERATURE (°C)

OFFSET VOLTAGE (mV)

VIN = V

COM

= V

DD

/ 2

Typical Operating Characteristics

(VDD= +5V for MAX7401, VDD= +3V for MAX7405; f

CLK

= 100kHz; SHDN = VDD; V

COM

= VOS= VDD/ 2; TA= +25°C; unless otherwise

noted.)

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,
Switched-Capacitor Filters

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VDD= +5V for MAX7401, VDD= +3V for MAX7405; f

CLK

= 100kHz; SHDN = VDD; V

COM

= VOS= VDD/ 2; TA= +25°C; unless otherwise

noted.)

0.96

0.98

0.97

1.00

0.99

1.03

1.02

1.01

1.04

-40 0-20 20 40 60 80 100

NORMALIZED OSCILLATOR FREQUENCY

vs. TEMPERATURE

MAX7401 toc10

TEMPERATURE (°C)

NORMALIZED OSCILLATOR FREQUENCY

C

OSC

= 390pF

MAX7405

MAX7401

-90

-70

-80

-50

-60

-40

-30

-10

-20

0

012

A

B

345

MAX7401

THD PLUS NOISE vs.

INPUT SIGNAL AMPLITUDE

MAX7401 toc11

AMPLITUDE (Vp-p)

THD + NOISE (dB)

NO LOAD

(SEE TABLE A)

-90

-70

-80

-50

-60

-40

-30

-10

-20

0

012345

MAX7401

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE AND RESISTIVE LOAD

MAX7401 toc12

AMPLITUDE (Vp-p)

THD + NOISE (dB)

RL = 500Ω

RL = 1kΩ

RL = 10kΩ

fIN = 200Hz
f

C

= 1kHz

MEASUREMENT BW = 22kHz

TRACE

f

IN

(Hz)

f

C

(kHz)

A 1000 5
B 200 1

f

CLK

(kHz)

500
100

MEASUREMENT

BANDWIDTH (kHz)

80
22

Table A. THD Plus Noise vs. Input
Signal Amplitude Test Conditions

-90

-70

-80

-40

-50

-60

-10

-20

-30

0

0 1.00.5 1.5 2.0 2.5 3.0

MAX7405

THD PLUS NOISE vs.

INPUT SIGNAL AMPLITUDE

MAX7401 toc13

AMPLITUDE (Vp-p)

THD + NOISE (dB)

B

NO LOAD
(SEE TABLE A)

A

-90

-70

-80

-40

-50

-60

-10

-20

-30

0

0 1.00.5 1.5 2.0 2.5 3.0

MAX7405

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE AND RESISTIVE LOAD

MAX7401 toc14

AMPLITUDE (Vp-p)

THD + NOISE (dB)

f

IN

= 200Hz

f

C

= 1kHz

MEASUREMENT BW = 22kHz

R

L

= 500Ω

RL = 1kΩ

RL = 10kΩ

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,

Switched-Capacitor Filters

_______________________________________________________________________________________ 7

NAME FUNCTION

1 COM

Common Input. Biased internally at mid-supply. 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 MAX7401, +3V for MAX7405

8 CLK

Clock Input. To override the internal oscillator, connect to an external clock; otherwise, connect an external
capacitor (C

OSC

) from CLK to GND to set the internal oscillator frequency.

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 externally. Connect OS to COM if no offset adjustment is
needed. Refer to

Offset and Common-Mode Input Adjustment

section.

5 OUT Filter Output

Pin Description

_______________Detailed Description

The MAX7401/MAX7405 Bessel filters provide low over­shoot and fast settling responses. Both parts operate
with a 100:1 clock-to-corner frequency ratio and a 5kHz
maximum corner frequency.

Lowpass Bessel filters such as the MAX7401/MAX7405
delay all frequency components equally, preserving the
shape of step inputs (subject to the attenuation of the
higher frequencies). Bessel filters settle quickly—an
important characteristic in applications that use a multi­plexer (mux) to select an input signal for an analog-to­digital converter (ADC). An anti-aliasing filter placed
between the mux and the ADC must settle quickly after
a new channel is selected.

Figure 1 shows the difference between Bessel and
Butterworth filters when a 1kHz square wave is applied
to the filter input. With the filter cutoff frequencies set at
5kHz, trace B shows the Bessel filter response and
trace C shows the Butterworth filter response.

Background Information

Most switched-capacitor filters (SCFs) are designed with
biquadratic sections. Each section implements two filter­ing poles, and the sections are 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. An alternative approach is to emulate a passive net­work using switched-capacitor integrators with summing
and scaling. Figure 2 shows a basic 8th-order ladder filter
structure.

A

2V/div

2V/div

2V/div

C

A: 1kHz INPUT SIGNAL
B: BESSEL FILTER RESPONSE; f

C

= 5kHz

C: BUTTERWORTH FILTER RESPONSE; f

C

= 5kHz

B

200µs/div

Figure 1. Bessel vs. Butterworth Filter Response

L3

L5 L7

C8

R2

C4C2

V

IN

+

-

V

0

L1

R1

C6

Figure 2. 8th-Order Ladder Filter Network

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,
Switched-Capacitor Filters

8 _______________________________________________________________________________________

A switched-capacitor filter such as the MAX7401/
MAX7405 emulates a passive ladder filter. The filter’s
component sensitivity is low when compared to a cas­caded biquad design because each component affects
the entire filter shape, not just one pole-zero pair. In other
words, a mismatched component in a biquad design will
have a concentrated error on its respective poles, while
the same mismatch in a ladder filter design results in an
error distributed over all poles.

Clock Signal

External Clock

The MAX7401/MAX7405 family of SCFs is designed for
use with external clocks that have a 40% to 60% duty
cycle. When using an external clock with these devices,
drive CLK with a CMOS gate powered from 0 to VDD.
Varying the rate of the external clock adjusts the corner
frequency of the filter as follows:

fC= f

CLK

/ 100

Internal Clock

When using the internal oscillator, connect a capacitor
(C

OSC

) between CLK and ground. The value of the

capacitor determines the oscillator frequency as follows:

where K = 38 for MAX7401 and K = 34 for MAX7405.
Minimize the stray capacitance at CLK so that it does

not affect the internal oscillator frequency. Vary the rate
of the internal oscillator to adjust 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 MAX7401/MAX7405’s input impedance is effectively
that of a switched-capacitor resistor and is inversely pro­portional to frequency. The input impedance values
determined below represent the average input imped­ance since the input current is not continuous. As a rule,
use a driver with an output impedance less than 10% of
the filter’s input impedance. Estimate the input imped­ance of the filter using the following formula:

where f

CLK

= clock frequency and CIN= 3.37pF.

Low-Power Shutdown Mode

These devices feature a shutdown mode that is activat­ed by driving SHDN low. In shutdown mode, the filter’s
supply current reduces to 0.2µA (typ) and its output
becomes high impedance. For normal operation, drive
SHDN high or connect to VDD.

___________Applications Information

Offset and Common-Mode

Input Adjustment

The voltage at COM sets the common-mode input volt­age and is biased at mid-supply with an internal resistor­divider. Bypass COM with a 0.1µF capacitor and
connect OS to COM. For applications requiring offset
adjustment or DC level shifting, apply an external bias
voltage through a resistor-divider network to OS, as
shown in Figure 3. (Note: Do not leave OS unconnect­ed.) The output voltage is represented by this equation:

V

OUT

= (VIN- V

COM

) + V

OS

with V

COM

= VDD/ 2 (typical), and where (VIN- V

COM

) is
lowpass filtered by the SCF, and VOSis added at the
output stage. See the

Electrical Characteristics

for the
voltage range of COM and OS. Changing the voltage on
COM or OS significantly from mid-supply reduces the fil­ter’s dynamic range.

Power Supplies

The MAX7401 operates from a single +5V supply, and
the MAX7405 operates from a single +3V supply.
Bypass VDDto GND with a 0.1µF capacitor. If dual sup­plies are required (±2.5V for MAX7401, ±1.5V for
MAX7405), connect COM to system ground and connect

Z

1

f C

IN

CLK IN

=

()

⋅

f (kHz)

K10

C

; C in pF

OSC

3

OSC

OSC

=

⋅

V

DD

V

SUPPLY

IN

CLK

GND

INPUT

OUTPUT

50k

50k

50k

OUT

0.1µF

0.1µF

0.1µF

CLOCK

SHDN

COM

OS

MAX7401
MAX7405

Figure 3. Offset Adjustment Circuit

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,

Switched-Capacitor Filters

_______________________________________________________________________________________ 9

GND to the negative supply. Figure 4 shows an example
of dual-supply operation. Single- and dual-supply perfor­mance are equivalent. For either single- or dual-supply
operation, drive CLK and SHDN from GND (V- in dual­supply operation) to VDD. For ±5V dual-supply applica­tions, use the MAX291–MAX297.

Input Signal Amplitude Range

The optimal input signal range is determined by observ­ing the voltage level at which the total harmonic distor­tion plus noise (THD+N) is minimized for a given corner
frequency. The

Typical Operating Characteristics

show
graphs of the devices’ THD+N response as the input
signal’s peak-to-peak amplitude is varied. These mea­surements are made with OS and COM biased at mid­supply.

Anti-Aliasing and Post-DAC Filtering

When using the MAX7401/MAX7405 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 fre­quencies around the clock frequency into the passband.
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 MAX7401/MAX7405’s typical harmonic-distortion
values with a 10kΩ load at TA= +25°C.

V

DD

V+

V-

IN

CLK

GND

INPUT

OUTPUTOUT

0.1µF

CLOCK

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

SHDN

COM

OS

0.1µF

MAX7401
MAX7405

*

V+
V-

Figure 4. Dual-Supply Operation

5th

3rd

-92-79

-93-83

500

100

f

CLK

(kHz)

4th

2nd

-92

-90

TYPICAL HARMONIC DISTORTION (dB)

-89

-91

4

5

1

MAX7401

V

IN

(Vp-p)

f

C

(kHz)

FILTER

1000

200

f

IN

(Hz)

Table 1. Typical Harmonic Distortion

TRANSISTOR COUNT: 1116

Chip Information

-88-82

-88-83

500

100

-88

-87

-83

-87

2

5

1

MAX7405

1000

200

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,
Switched-Capacitor Filters

10 ______________________________________________________________________________________

________________________________________________________Package Information

SOICN.EPS

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,

Switched-Capacitor Filters

______________________________________________________________________________________ 11

Package Information (continued)

PDIPN.EPS

MAX7401/MAX7405

8th-Order, Lowpass, Bessel,
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

© 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

NOTES