MAX7427EUA+T - Maxim Integrated Products, Inc.

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 fre-

quencies from 1Hz to 12kHz, making them ideal for

low-power post-DAC filtering and anti-aliasing applica-

tions. 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

OUTVDD

CLK

SHDNIN

GND

COM

µMAX/PDIP

TOP VIEW

MAX7426

MAX7427

VDD

CLK

OUT

GND

INPUT

0.1µF

CLOCK

SHDN

OUTPUT

COM

MAX7426

MAX7427

VSUPPLY

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

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 1-800-998-8800.

For small orders, phone 1-800-835-8769.

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 = 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.......................................................1s

Continuous Power Dissipation (TA= +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

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

13.5 17.5 21.5fOSC

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

90 130RCOM

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 9fC

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

±8 ±12.5ICLK

Clock Output Current

(internal oscillator mode)

µA

kHz

µA

kΩ

mVp-p

kΩ

V/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 = 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—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, 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

0.8 1.0Supply Current IDD

4.5 5.5VDD

Supply Voltage

µA

UNITS

SHDN Input Leakage Current VSHDN = 0 to VDD ±0.2 ±10 µA

VOS

Input Voltage Range at OS

90 130RCOM

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 12fC

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

kΩ

mVp-p

V/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

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

4 _______________________________________________________________________________________

COSC = 1000pF (Note 3)

CONDITIONS

13.5 17.5 21.5fOSC

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

0.75 1.0

2.7 3.6VDD

Supply Voltage

0.5VIL

Clock Input Low

2.5VIH

Clock Input High

±7.5 ±12.5ICLK

Clock Output Current

(internal oscillator mode)

µA

kHz

UNITS

SHDN Input Leakage Current VSHDN = 0 to VDD ±0.2 ±10 µA

ELECTRICAL CHARACTERISTICS—MAX7427 (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.)

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 = 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 sinu-

soidal input at 0.2fC.

Note 2: DC insertion gain is defined as ∆VOUT / ∆VIN.

Note 3: fOSC (kHz) ≈ 17.5 ✕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

-0.4 -0.2 0.4

Insertion Gain

with DC Gain Error Removed

(Note 4)

-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

mAIDD

Supply Current

CLOCK

POWER REQUIREMENTS

SHUTDOWN

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________ 5

-70

-60

-40

-50

-10

-20

-30

012345

FREQUENCY RESPONSE

MAX7426/27-02

INPUT FREQUENCY (kHz)

GAIN (dB)

fC = 1kHz

r = 1.25

Typical Operating Characteristics

(VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA= +25°C, unless other-

wise noted.)

-1.0

-0.6

-0.8

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 0.2 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

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA= +25°C, unless other-

wise noted.)

-90

-70

-80

-50

-60

-40

-30

-10

-20

012345

MAX7426

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. INPUT SIGNAL AMPLITUDE

MAX7426/27-10

AMPLITUDE (Vp-p)

THD + NOISE (dB)

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

SEE TABLE 1.

Table 1. THD + Noise Test Conditions

LABEL fIN

(Hz)

(kHz)

A200 1

B1k 5

fCLK

(kHz)

100

500

MEASUREMENT

BANDWIDTH (kHz)

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor

_______________________________________________________________________________________ 7

16.0

16.4

17.2

16.8

17.6

18.0

-40 0 20-20 40 60 80 100

INTERNAL OSCILLATOR FREQUENCY

vs. TEMPERATURE

MAX7426/27-16

TEMPERATURE (°C)

OSCILLATOR FREQUENCY (kHz)

VDD = +3V

COSC = 1000pF

VDD = +5V

0 150 20050 100 250 300 350

INTERNAL OSCILLATOR PERIOD

vs. LARGE CAPACITANCE (IN nF)

MAX7426/27-14

CAPACITANCE (nF)

OSCILLATOR PERIOD (ms)

VDD = +5V

VDD = +3V

17.1

17.2

17.3

17.4

17.5

2.0 3.02.5 3.5 4.0 4.5 5.0 5.5

INTERNAL OSCILLATOR FREQUENCY

vs. SUPPLY VOLTAGE

MAX7426/27-15

SUPPLY VOLTAGE (V)

OSCILLATOR FREQUENCY (kHz)

COSC = 1000pF

-3.5

-2.5

-3.0

-1.5

-2.0

-0.5

-1.0

-40 0 20-20 40 60 80 100

DC OFFSET VOLTAGE

vs. TEMPERATURE

MAX7426/27-17

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

2.5 3.53.0 4.0 4.5 5.0 5.5

DC OFFSET VOLTAGE

vs. SUPPLY VOLTAGE

MAX7426/27-18

SUPPLY VOLTAGE (V)

DC OFFSET VOLTAGE (mV)

Typical Operating Characteristics (continued)

(VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA= +25°C, unless other-

wise noted.)

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

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 stop-

band rejection. All parts operate with a 100:1 clock-to-

corner 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 fil-

ters. The advantage to this approach is ease of design.

However, this type of design is highly sensitive to com-

ponent variations if any section’s Q is high. The

MAX7426/MAX7427 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 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-alias-

ing 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 transmis-

sion zero causes the filter’s amplitude to drop to a mini-

mum level. Beyond this zero, the response rises as the

frequency increases until the next transmission zero.

The stopband begins at the stopband frequency, fS. At

frequencies above fS, the filter’s gain does not exceed

the gain at fS. The corner frequency, fC, is defined as

the point where the filter output attenuation falls just

below the passband ripple. The transition ratio (r) is

defined as the ratio of the stopband frequency to the

corner frequency:

r = fS / fC

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

C4C2

C5C3C1VIN

-RL

Figure 1. 5th-Order Ladder Elliptic Filter Network

NAME FUNCTION

1COM 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.

2IN Filter Input

3GND Ground

4 VDD Positive Supply Input, +5V for MAX7426 or +3V for MAX7427

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

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

(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 MAX7426/MAX7427’s input impedance is effective-

ly that of a switched-capacitor resistor (see the following

equation), and is inversely proportional to frequency.

The input impedance values determined by the equa-

tion 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 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 opera-

tion, 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, 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

( )

()

=− +

Z 1

f C

IN CLK IN

=×

f (kHz)

17.5 10

C (pF)

OSC

=×

CCLK

=100

PASSBAND STOPBAND

GAIN (dB)

FREQUENCY

fCfS

TRANSITION RATIO =

RIPPLE

VDD

VSUPPLY

CLK

GND

INPUT

OUTPUT

50k

OUT

0.1µF

CLOCK

SHDN

COM

MAX7426

MAX7427

Figure 2. Elliptic Filter Response Figure 3. Offset Adjustment Circuit

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 signifi-

cantly 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 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 4

shows an example of dual-supply operation. Single-

supply and dual-supply performance are equivalent.

For either single-supply or dual-supply operation, drive

CLK and SHDN from GND (V- in dual-supply operation)

to 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 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 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 10kΩload at

TA= +25°C.

VDD

V+

V-

CLK

GND

INPUT

OUTPUTOUT

0.1µF

CLOCK

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

SHDN

COM

0.1µF

MAX7426

MAX7427

V+

V-

Figure 4. Dual-Supply Operation

Table 2. Typical Harmonic Distortion

FILTER fIN

(Hz)

VIN

(Vp-p) 2nd 4th

fCLK

(kHz)

TYPICAL HARMONIC DISTORTION (dB)

3rd 5th

MAX7426 1k

200 4

500

100

-73-71

-88

-90

-92

MAX7427 200 2

500

100

-87

-90

-82

-86

-87

-88

-90

TRANSISTOR COUNT: 1457

PROCESS: BiCMOS

Chip Information

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

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PDIPN.EPS