Rainbow Electronics MAX7407 User Manual

General Description

The MAX7400/MAX7403/MAX7404/MAX7407 8th-order,
lowpass, elliptic, switched-capacitor filters (SCFs) oper­ate from a single +5V (MAX7400/MAX7403) or +3V
(MAX7404/MAX7407) supply. These devices draw 2mA
of supply current and allow corner frequencies from
1Hz to 10kHz, making them ideal for low-power anti­aliasing and post-DAC filtering applications. They fea­ture a shutdown mode that reduces the 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. In addition,
an offset adjustment pin (OS) allows for the adjustment
of the DC output level.

The MAX7400/MAX7404 provide 82dB of stopband
rejection and a sharp rolloff with a transition ratio of 1.5.
The MAX7403/MAX7407 provide a sharper rolloff with a
transition ratio of 1.2, while still delivering 60dB of stop­band rejection. The fixed response of these devices
simplifies the design task to corner-frequency selection
by setting a clock frequency. The MAX7400/
MAX7403/MAX7404/MAX7407 are available in 8-pin SO
and DIP packages.

Applications

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

Features

♦ 8th-Order Lowpass Elliptic Filter
♦ Low Noise and Distortion

-82dB THD + Noise (MAX7400)

♦ Clock-Tunable Corner Frequency (1Hz to 10kHz)
♦ 100:1 Clock-to-Corner Ratio
♦ Single-Supply Operation

+5V (MAX7400/MAX7403)
+3V (MAX7404/MAX7407)

♦ Low Power

2mA (Operating Mode)

0.2µA (Shutdown Mode)

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

MAX7400/MAX7403/MAX7404/MAX7407

8th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

________________________________________________________________

Maxim Integrated Products

1

V

DD

IN

CLK

OUT

GND

INPUT

0.1µF

0.1µF

CLOCK

SHDN

OUTPUT

V

SUPPLY

COM

OS

MAX7400
MAX7403
MAX7404
MAX7407

Typical Operating Circuit

19-4764; Rev 2; 6/99

Ordering Information continued at end of data sheet.

Pin Configuration

Ordering Information

Selector Guide

MAX7407 Elliptic (r = 1.2) +3

PART FILTER RESPONSE

OPERATING

VOLTAGE (V)

MAX7403

MAX7400 Elliptic (r = 1.5) +5

Elliptic (r = 1.2) +5

MAX7404 Elliptic (r = 1.5) +3

PART

MAX7400CSA

MAX7400CPA
MAX7400ESA -40°C to +85°C

0°C to +70°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

8 SO
8 Plastic DIP
8 SO

MAX7400EPA -40°C to +85°C 8 Plastic DIP

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

TOP VIEW

COM

1

GND

2

MAX7400
MAX7403

3

MAX7404
MAX7407

4

DD

SO/DIP

87CLK

SHDNIN

OS

6

OUTV

5

MAX7400/MAX7403/MAX7404/MAX7407

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

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS—MAX7400/MAX7403

(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 +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

MAX7400/MAX7403 ..............................................-0.3V to +6V

MAX7404/MAX7407 ..............................................-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)

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

DIP (derate 9.1mW/°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

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

(Note 1)

SHDN = GND, V

COM

= 0 to V

DD

VIN= V

COM

= VDD/ 2

Output, COM internally biased

V

COM

= VDD/ 2 (Note 2)

Input, COM externally driven

CONDITIONS

µA±0.1 ±10Input Leakage Current at OS

µA±0.1 ±10Input Leakage Current at COM

pF50 500C

L

Maximum Capacitive Load
at OUT

kΩ10 1R

L

Resistive Output Load Drive

mVp-p10Clock Feedthrough

kΩ75 125R

COM

Input Resistance at COM

VDD/ 2

V

DD

/ 2

V

DD

/ 2

- 0.2 + 0.2

V

COM

COM Voltage Range V

VDD/ 2

V

DD

/ 2

V

DD

/ 2

- 0.5 + 0.5

100:1f

CLK/fC

Clock-to-Corner Ratio

kHz0.001 to 10f

C

Corner Frequency

VV

COM

±0.1V

OS

Input Voltage Range at OS

-82

ppm/°C10Clock-to-Corner Tempco

V0.25 VDD- 0.25Output Voltage Range

mV±5 ±25V

OFFSET

Output Offset Voltage

dB-0.1 0.15 0.3

DC Insertion Gain with
Output Offset Removed

UNITSMIN TYP MAXSYMBOLPARAMETER

C

OSC

= 1000pF (Note 4) kHz29 38 48f

OSC

Internal Oscillator Frequency

V

CLK

= 0 or 5V µA±15 ±30I

CLK

Clock Input Current

VDD- 0.5V

IH

V

0.5V

IL

Clock Input High

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

dB

-80

THD+N

Total Harmonic Distortion
plus Noise

MAX7400
MAX7403

V/V1A

OS

OS Voltage Gain to OUT

Clock Input Low V

FILTER CHARACTERISTICS

CLOCK

MAX7400/MAX7403/MAX7404/MAX7407

8th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS—MAX7400/MAX7403 (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—MAX7404/MAX7407

(VDD= +3V, 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.)

SHUTDOWN

POWER REQUIREMENTS

SHDN Input Leakage Current

±0.1 ±10 µAV

SHDN

= 0 to V

DD

SHDN Input High

V

SDL

0.5

VV

SDH

VDD- 0.5

PARAMETER SYMBOL MIN TYP MAX UNITS

Power-Supply Rejection Ratio PSRR 60 dB

Shutdown Current I

SHDN

0.2 1 µA

Supply Voltage V

DD

4.5 5.5 V

Supply Current I

DD

2 3.5 mA

CONDITIONS

Measured at DC

SHDN = GND, CLK driven from 0 to V

DD

Operating mode, no load, IN = OS = COM

FILTER CHARACTERISTICS

Total Harmonic Distortion
plus Noise

PARAMETER SYMBOL MIN TYP MAX UNITS

DC Insertion Gain with Output
Offset Removed

-0.1 0.1 0.3 dB

Output Offset Voltage V

OFFSET

±5 ±25 mV

Output Voltage Range 0.25 VDD- 0.25 V

Clock-to-Corner Tempco 10 ppm/°C

THD+N

-77

dB

MAX7407

MAX7404 -79

OS Voltage Gain to OUT A

OS

1 V/V

Input Voltage Range at OS V

OS

V

COM

±0.1 V

Corner Frequency f

C

0.001 to 10 kHz

Clock-to-Corner Ratio f

CLK/fC

100:1

VDD/ 2

V

DD

/ 2

V

DD

/ 2

- 0.1 + 0.1

VCOM Voltage Range V

COM

Input Resistance at COM R

COM

75 125 kΩ
Clock Feedthrough 10 mVp-p
Resistive Output Load Drive R

L

10 1 kΩ
Maximum Capacitive Load

at OUT

C

L

50 500 pF
Input Leakage Current at COM ±0.1 ±10 µA

Input Leakage Current at OS ±0.1 ±10 µA

CONDITIONS

COM internally biased or externally driven

V

COM

= VDD/ 2 (Note 2)

VIN= V

COM

= VDD/ 2

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

SHDN = GND, V

COM

= 0 to V

DD

(Note 1)

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

SHDN Input Low

V

MAX7400/MAX7403/MAX7404/MAX7407

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

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS—MAX7404/MAX7407 (continued)

(VDD= +3V, 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.)

ELLIPTIC (r = 1.5) FILTER CHARACTERISTICS—MAX7400/MAX7404

(VDD= +5V for MAX7400, VDD= +3V for MAX7404; filter output measured at OUT; 10kΩ || 50pF load to GND at OUT; SHDN = VDD;
V

COM

= VOS= V

DD

/ 2; f

CLK

= 100kHz; TA= T

MIN

to T

MAX

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

V

CLK

= 0 or 3V

C

OSC

= 1000pF (Note 4)

V

CONDITIONS

VDD- 0.5V

IH

µA±15 ±30I

CLK

Clock Input Current

kHz26 34 43f

OSC

Internal Oscillator Frequency

0.5V

IL

Clock Input High

UNITSMIN TYP MAXSYMBOLPARAMETER

SHDN = GND, CLK driven from 0 to V

DD

Operating mode, no load, IN = OS = COM

Measured at DC

µA0.2 1I

SHDN

mA2 3.5I

DD

Supply Current

V2.7 3.6V

DD

Supply Voltage

60PSRR

Shutdown Current
Power-Supply Rejection Ratio dB

VDD- 0.5V

SDH

SHDN Input High

V

V

SHDN

= 0 to V

DD

±0.1 ±10

SHDN Input Leakage Current

µA

V

SDL

0.5

Clock Input Low

SHDN Input Low

V

V

CLOCK

POWER REQUIREMENTS

SHUTDOWN

dB

CONDITIONS UNITSMIN TYP MAXPARAMETER

fIN= 0.371f

C

-0.20 -0.10 0.20

fIN= 0.737f

C

fIN= 0.587f

C

-0.20 -0.08 0.20

-0.20 0.02 0.20

fIN= 0.940f

C

fIN= 0.868f

C

-0.20 -0.03 0.20

fIN= 1.000f

C

fIN= 0.988f

C

-0.20 0.02 0.25

-0.20 0.09 0.25

-0.20 0.06 0.20

fIN= 1.601f

C

fIN= 1.500f

C

-84 -78

fIN= 4.020f

C

fIN= 2.020f

C

-85 -78

Insertion Gain Relative to DC Gain
(Note 5)

-83 -78

-82 -75

8th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________ 5

Note 1: The maximum fCis defined as the clock frequency, f

CLK

= 100 · fC, at 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: OS voltages above V

DD

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

Note 4: For MAX7400/MAX7403, f

OSC

(kHz) ≅ 38 · 103 / C

OSC

(pF). For MAX7404/MAX7407, f

OSC

(kHz) ≅ 34 · 103 / C

OSC

(pF).

Note 5: The input frequencies, f

IN

, are selected at the peaks and troughs of the frequency responses.

ELLIPTIC (r = 1.2) FILTER CHARACTERISTICS—MAX7403/MAX7407

(VDD= +5V for MAX7403, VDD= +3V for MAX7407; filter output measured at OUT; 10kΩ || 50pF load to GND at OUT; SHDN = VDD;
V

COM

= VOS= V

DD

/ 2; f

CLK

= 100kHz; TA= T

MIN

to T

MAX

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

Typical Operating Characteristics

(VDD= +5V for MAX7400/MAX7403, VDD= +3V for MAX7404/MAX7407; V

COM

= VOS= VDD/ 2; SHDN = VDD; f

CLK

= 100kHz;

T

A

= +25°C; unless otherwise noted.)

-120

-80

-100

-40

-60

0

-20

20

012345

MAX7400/MAX7404 (r = 1.5)

FREQUENCY RESPONSE

MAX7400/03-01

INPUT FREQUENCY (kHz)

GAIN (dB)

fC = 1kHz

-0.08

0

-0.04

0.12

0.08

0.04

0.20

0.16

0.24

0 202 404 606 808 1010

MAX7400/MAX7404 (r = 1.5)

PASSBAND FREQUENCY RESPONSE

MAX7400/03-02

INPUT FREQUENCY (Hz)

GAIN (dB)

fC = 1kHz

-640

-480

-560

-240

-320

-400

-80

-160

0

0 300 600 900 1200 1500

MAX7400/MAX7404 (r = 1.5)

PHASE RESPONSE

MAX7400/03-03

INPUT FREQUENCY (Hz)

PHASE SHIFT (DEGREES)

fC = 1kHz

PARAMETER MIN TYP MAX UNITS

-58 -50

-60 -54

Insertion Gain Relative to DC Gain
(Note 5)

-60 -54

fIN= 1.533f

C

dB

fIN= 2.875f

C

-59 -54

fIN= 1.200f

C

fIN= 1.261f

C

-0.20 0.10 0.20

-0.20 0.14 0.30

CONDITIONS

-0.20 0.09 0.30

fIN= 0.992f

C

fIN= 1.000f

C

-0.20 0.02 0.20

fIN= 0.902f

C

fIN= 0.956f

C

-0.20 0.02 0.20

-0.20 -0.06 0.20

fIN= 0.640f

C

fIN= 0.784f

C

-0.20 -0.11 0.20fIN= 0.408f

C

MAX7400/MAX7403/MAX7404/MAX7407

MAX7400/MAX7403/MAX7404/MAX7407

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

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VDD= +5V for MAX7400/MAX7403, VDD= +3V for MAX7404/MAX7407; V

COM

= VOS= VDD/ 2; SHDN = VDD; f

CLK

= 100kHz;

T

A

= +25°C; unless otherwise noted.)

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

MAX7400 toc07

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

NO LOAD

MAX7404
MAX7407

MAX7400
MAX7403

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

MAX7400 toc08

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

NO LOAD

MAX7400
MAX7403

MAX7404
MAX7407

-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

MAX7400 toc09

SUPPLY VOLTAGE (V)

OFFSET VOLTAGE (mV)

VIN = V

COM

= VDD/2

MAX7404
MAX7407

MAX7400
MAX7403

-0.5

0

0.5

1.5

1.0

2.0

-40 -20 0 20 40 60 80 100

OFFSET VOLTAGE vs. TEMPERATURE

MAX7400/03-10

TEMPERATURE (°C)

OFFSET VOLTAGE (mV)

VIN = V

COM

= VDD/2

-90

-70

-80

-50

-60

-40

-30

-10

-20

0

012345

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE (MAX7400)

MAX7400/03 11

AMPLITUDE (Vp-p)

THD + NOISE (dB)

NO LOAD

(SEE TABLE A)

B

C

D

-90

-70

-80

-50

-60

-40

-30

-10

-20

0

012345

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE AND RESISTIVE LOAD (MAX7400)

MAX7400/03-12

AMPLITUDE (Vp-p)

THD + NOISE (dB)

fIN = 200Hz
f

C

= 1kHz

MEASUREMENT BW = 22kHz

RL = 500Ω

RL = 1kΩ

RL = 10kΩ

-120

-80

-100

-60

0

20

-20

-40

40

012345

MAX7403/MAX7407 (r = 1.2)

FREQUENCY RESPONSE

MAX7400/03 04

INPUT FREQUENCY (kHz)

GAIN (dB)

fC = 1kHz

-0.32

-0.16

-0.24

-0.08

0.16

0.24

0.08
0

0.32

0 202 404 606 808 1010

MAX7403/MAX7407 (r = 1.2)

PASSBAND FREQUENCY RESPONSE

MAX7400/03 05

INPUT FREQUENCY (Hz)

GAIN (dB)

fC = 1kHz

-640

-480

-560

-400

-160

-80

-240

-320

0

0 240 480 720 960 1200

MAX7403/MAX7407 (r = 1.2)

PHASE RESPONSE

MAX7400/03 06

INPUT FREQUENCY (Hz)

PHASE SHIFT (DEGREES)

fC = 1kHz

MAX7400/MAX7403/MAX7404/MAX7407

8th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________

7

-90

-70

-80

-50

-60

-40

-30

-10

-20

0

012345

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE (MAX7403)

MAX7400/03 13

AMPLITUDE (Vp-p)

THD + NOISE (dB)

NO LOAD
(SEE TABLE A)

B

C

D

-90

-70

-80

-50

-60

-40

-30

-10

-20

0

012345

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE AND RESISTIVE LOAD (MAX7403)

TABLE A. THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE TEST CONDITIONS

MAX7400/03 14

AMPLITUDE (Vp-p)

THD + NOISE (dB)

fIN = 200Hz
f

C

= 1kHz

MEASUREMENT BW = 22kHz

RL = 500Ω

R

L =

1kΩ

RL = 10kΩ

TRACE

f

IN

(Hz)

f

C

(kHz)

f

CLK

(kHz)

MEASUREMENT

BANDWIDTH (kHz)

A

B

C

2800

2000

1000

14

10

5

1400

1000

500

80

80

80

D 200 1 100 22

Typical Operating Characteristics (continued)

(VDD= +5V for MAX7400/MAX7403, VDD= +3V for MAX7404/MAX7407; V

COM

= VOS= VDD/ 2; SHDN = VDD; f

CLK

= 100kHz;

T

A

= +25°C; unless otherwise noted.)

-90

-70

-80

-40

-50

-60

-10

-20

-30

0

0 1.00.5 1.5 2.0 2.5 3.0

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE AND RESISTIVE LOAD (MAX7404)

MAX7400 toc16

AMPLITUDE (Vp-p)

THD + NOISE (dB)

RL = 10kΩ

RL = 1kΩ

RL = 500Ω

fIN = 200Hz
f

C

= 1kHz

MEASUREMENT BW = 22kHz

-90

-70

-80

-40

-50

-60

-10

-20

-30

0

0 1.00.5 1.5 2.0 2.5 3.0

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE (MAX7407)

MAX 7400 toc17

AMPLITUDE (Vp-p)

THD + NOISE (dB)

NO LOAD
(SEE TABLE A)

A

B

C

D

-90

-70

-80

-40

-50

-60

-10

-20

-30

0

0 1.00.5 1.5 2.0 2.5 3.0

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE AND RESISTIVE LOAD (MAX7407)

MAXX7400 toc18

AMPLITUDE (Vp-p)

THD + NOISE (dB)

RL = 500Ω

fIN = 200Hz
f

C

= 1kHz

MEASUREMENT BW = 22kHz

RL = 10kΩ

RL = 1kΩ

-90

-70

-80

-40

-50

-60

-10

-20

-30

0

0 1.00.5 1.5 2.0 2.5 3.0

THD PLUS NOISE vs. INPUT SIGNAL

AMPLITUDE (MAX7404)

MAX7400 toc15

AMPLITUDE (Vp-p)

THD + NOISE (dB)

B

NO LOAD
(SEE TABLE A)

C

D

A

Pin Description

PIN

Common Input. Biased internally at midsupply. Bypass externally to GND with a 0.1µF capacitor. To over­ride internal biasing, drive with an external supply.

COM1

FUNCTIONNAME

Filter InputIN2

Positive Supply Input: +5V for MAX7400/MAX7403, +3V for MAX7404/MAX7407V

DD

4

GroundGND3

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.

OS6

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.

CLK8

Shutdown Input. Drive low to enable shutdown mode; drive high or connect to VDDfor normal operation.

SHDN

7

Filter OutputOUT5

MAX7400/MAX7403/MAX7404/MAX7407

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

8 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VDD= +5V for MAX7400/MAX7403, VDD= +3V for MAX7404/MAX7407; V

COM

= VOS= VDD/ 2; SHDN = VDD; f

CLK

= 100kHz;

T

A

= +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

MAX7400 toC21

TEMPERATURE (°C)

NORMALIZED OSCILLATOR FREQUENCY

C

OSC

= 390pF

MAX7400
MAX7403

MAX7404
MAX7407

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

MAX7400 toc20

SUPPLY VOLTAGE (V)

NORMALIZED OSCILLATOR FREQUENCY

C

OSC

= 390pF

MAX7400
MAX7403

MAX7404
MAX7407

0.1

1

100

10

1000

10,000

0.0110.1

10

100

1000

INTERNAL OSCILLATOR FREQUENCY

vs. C

OSC

CAPACITANCE

MAX7400 toc19

C

OSC

CAPACITANCE (nF)

OSCILLATOR FREQUENCY (kHz)

MAX7400/MAX7403/MAX7404/MAX7407

8th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________ 9

Detailed Description

The MAX7400/MAX7403/MAX7404/MAX7407 family of
8th-order, lowpass filters provides sharp rolloff with
good stopband rejection. All parts operate with a
100:1 clock-to-corner frequency ratio and a 10kHz
maximum corner frequency. These devices accept a
single +5V (MAX7400/MAX7403) or +3V (MAX7404/
MAX7407) supply. Figure 1 shows the functional dia­gram.

Most switched-capacitor filters (SFCs) are designed
with biquadratic sections. Each section implements two
filtering poles, and the sections can be cascaded to
produce higher-order filters. The advantage of 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 MAX7400 family uses an alter­native approach, which is to emulate a passive network
using switched-capacitor integrators with summing and
scaling. The passive network can be synthesized using
CAD programs or can be found in many filter books.
Figure 2 shows a basic 8th-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 MAX7400/MAX7403/
MAX7404/MAX7407 provide the steepest possible rolloff
with frequency of the four most common filter types
(Butterworth, Bessel, Chebyshev, and Elliptic). Figure 3
shows the 8th-order elliptic filter response. 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, f

C

, is defined as the point where
the filter output attenuation falls just below the passband
ripple. The transition ratio is defined as the ratio of the
stopband frequency to the corner frequency:

r = fS/ f

C

The MAX7400/MAX7404 have a transition ratio of 1.5
and a typical stopband rejection of 82dB. The
MAX7403/MAX7407 have a transition ratio of 1.2 (pro­viding the steepest rolloff) and a typical stopband
rejection of 60dB.

2

INT

CLOCK

IN

1

COM

8

CLK

SHDN

7
4

5

6

3

V

DD

OUT

OS

GND

BIAS

SCF

LOGIC

OFFSET

ADJ

MAX7400
MAX7403
MAX7404
MAX7407

V

DD

Figure 1. Functional Diagram

C10

C11

C9

L3

L5 L7

C8

R2

C4C2

V

IN

+

-

V

0

L1

R1

C6

Figure 2. 8th-Order Ladder Filter Network

V

DD

V

SUPPLY

IN

CLK

GND

INPUT

OUTPUT

50k

50k

50k

OUT

0.1µF

0.1µF

0.1µF

CLOCK

SHDN

COM

OS

MAX7400
MAX7403
MAX7404
MAX7407

Figure 4. Offset Adjustment Circuit

MAX7400/MAX7403/MAX7404/MAX7407

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

10 ______________________________________________________________________________________

Clock Signal

External Clock

The MAX7400/MAX7403/MAX7404/MAX7407 SCFs
were designed for use with external clocks that have a
40% to 60% duty cycle. When using an external clock,
drive CLK with a CMOS gate powered from 0 to VDD.
Varying the rate of the external clock adjusts the filter
corner frequency:

fC= f

CLK

/ 100

Internal Clock

When using the internal oscillator, the capacitance
(C

OSC

) on the CLK pin determines the oscillator fre-

quency:

where K = 38 for the MAX7400/MAX7403, and K = 34
for the MAX7404/MAX7407. Since the capacitor value
is in 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 MAX7400/MAX7403/MAX7404/MAX7407’s input
impedance is effectively that of a switched-capacitor
resistor and is inversely proportional to frequency. The

input impedance determined by the following equation
represents the average input impedance, since the
input current is not continuous. As a rule, use a driver
with an output source 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=0.85pF.

Low-Power Shutdown Mode

These devices feature a shutdown mode that is activat­ed by driving SHDN low. Placing the filter in shutdown
mode reduces the supply current to 0.2µA (typ) and
places the output of the filter into a high-impedance
state. 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 internally biased at midsupply by a 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 4. (Note: Do not leave OS unconnect­ed.) The output voltage is represented by the following
equation:

V

OUT

= (VIN- V

COM

) + V

OS

Z

fC

IN

CLK IN

()

( )

Ω=

⋅

1

f (kHz) =

K 10

C

OSC

3

OSC

⋅

; CinpF

OSC

PASSBAND STOPBAND

GAIN (dB)

FREQUENCY

f

CfS

f

S

f

C

f

S

f

C

TRANSITION RATIO =

RIPPLE

Figure 3. Elliptic Filter Response

MAX7400/MAX7403/MAX7404/MAX7407

8th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

______________________________________________________________________________________ 11

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
COM and OS input voltage ranges. Changing the volt­age on COM or OS significantly from midsupply
reduces the filter’s dynamic range.

Power Supplies

The MAX7400/MAX7403 operate from a single +5V
supply. The MAX7404/MAX7407 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
5 shows an example of dual-supply operation. Single­supply and dual-supply performance are equivalent.
For single-supply or dual-supply operation, drive CLK
and SHDN from GND (V- in dual-supply operation) to
VDD. For a ±2.5V supply, use the MAX7400 or MAX7403;
for a ±1.5V supply, use MAX7404 or MAX7407. For ±5V
dual-supply applications, use the MAX291–MAX297.

Input Signal Amplitude Range

The ideal 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 Character-

istics

show 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 MAX7400/MAX7403/MAX7404/
MAX7407 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. Such 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 and
an input signal of 4Vp-p (MAX7400/MAX7403) or 2Vp-p
(MAX7404/MAX7407), 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

MAX7400
MAX7403
MAX7404
MAX7407

*

V+

V-

Figure 5. Dual-Supply Operation

2nd

-88100

TYPICAL

HARMONIC

DISTORTION (dB)

1

f

C

(kHz)

-89100

200

1

-84

f

IN

(Hz)

200

4th3rd 5th

-89500

MAX7400

5 1000

-86-89-82

-88-93-77

500

MAX7403

5 1000

-87-91

FILTER

-81

-91-90-80

4

V

IN

(Vp-p)

4

f

CLK

(kHz)

-85100 1 200

-85500

MAX7404

5 1000

-86-85-82

-84-86-81

2

-85100 1 200

-86500

MAX7407

5 1000

-86-85-82

-86-85-84

2

Table 1. Typical Harmonic Distortion

MAX7400/MAX7403/MAX7404/MAX7407

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

Package Information

SOICN.EPS

TRANSISTOR COUNT: 1116

Ordering Information (continued) Chip Information

PART

MAX7403CSA

MAX7403CPA
MAX7403ESA -40°C to +85°C

0°C to +70°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

8 SO
8 Plastic DIP

8 SO
MAX7403EPA -40°C to +85°C 8 Plastic DIP
MAX7404CSA
MAX7404CPA
MAX7404ESA -40°C to +85°C

0°C to +70°C

0°C to +70°C 8 SO

8 Plastic DIP

8 SO
MAX7404EPA -40°C to +85°C 8 Plastic DIP
MAX7407CSA
MAX7407CPA
MAX7407ESA -40°C to +85°C

0°C to +70°C

0°C to +70°C 8 SO

8 Plastic DIP

8 SO
MAX7407EPA -40°C to +85°C 8 Plastic DIP

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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