Maxim MAX7427EPA 5th-order, lowpass, elliptic, switched-capacitor filter Datasheet

19-1710; Rev 0; 4/00
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
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
Applications
Ordering Information
ADC Anti-Aliasing
CT2 Base Stations
PART
TEMP. RANGE
Post-DAC Filtering
Speech Processing
MAX7426CUA
0°C to +70°C
MAX7426CPA
MAX7426EUA
MAX7426EPA
MAX7427CUA
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
MAX7427CPA
MAX7427EUA
MAX7427EPA
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
Selector Guide
TRANSITION RATIO
OPERATING
VOLTAGE (V)
MAX7426
r = 1.25
+5
MAX7427
r = 1.25
+3
PART
PIN-PACKAGE
8 µMAX
8 Plastic DIP
8 µMAX
8 Plastic DIP
0°C to +70°C
8 µMAX
8 Plastic DIP
8 µMAX
8 Plastic DIP
Pin Configuration
Typical Operating Circuit
VSUPPLY
TOP VIEW
0.1µF
VDD
INPUT
IN
COM 1
SHDN
OUT
OUTPUT
IN 2
GND
MAX7426
MAX7427
CLOCK
CLK
VDD 4
COM
GND
OS
3
MAX7426
MAX7427
0.1µF
8
CLK
7
SHDN
6
OS
5
OUT
µMAX/PDIP
________________________________________________________________ Maxim Integrated Products
1
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For small orders, phone 1-800-835-8769.
MAX7426/MAX7427
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.
MAX7426/MAX7427
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
ABSOLUTE MAXIMUM RATINGS
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
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.
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.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
FILTER
Corner-Frequency Range
Clock-to-Corner Ratio
fC
(Note 1)
0.001 to 9
fCLK/fC
Clock-to-Corner Tempco
10
Output Voltage Range
Output Offset Voltage
0.25
VOFFSET
DC Insertion Gain with Output
Offset Removed
Total Harmonic Distortion plus
Noise
Offset Voltage Gain
COM Voltage Range
Input Voltage Range at OS
Input Resistance at COM
kHz
100:1
VIN = VCOM = VDD / 2
VCOM = VDD / 2 (Note 2)
THD+N
AOS
fIN = 200Hz, VIN = 4Vp-p,
measurement bandwidth = 22kHz
V
±25
mV
0.2
0.4
dB
dB
+1
V/V
Input, COM externally driven
VDD
- 0.5
2
VDD
2
VDD
+ 0.5
2
Output, COM internally driven
VDD
- 0.2
2
VDD
2
VDD
+ 0.2
2
V
Measured with respect to COM
RCOM
Clock Feedthrough
VDD - 0.25
±4
-81
OS to OUT
VCOM
VOS
0
ppm/°C
±0.1
90
TA = +25°C
V
130
kΩ
5
mVp-p
Resistive Output Load Drive
RL
10
1
kΩ
Maximum Capacitive Load
at OUT
CL
50
500
pF
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
17.5
21.5
kHz
±8
±12.5
µA
CLOCK
Internal Oscillator Frequency
fOSC
Clock Output Current
(internal oscillator mode)
ICLK
Clock Input High
VIH
Clock Input Low
VIL
2
COSC = 1000pF (Note 3)
13.5
4.5
_______________________________________________________________________________________
V
0.5
V
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
(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.)
PARAMETER
CONDITIONS
SYMBOL
MIN
TYP
MAX
UNITS
POWER REQUIREMENTS
Supply Voltage
VDD
Supply Current
IDD
5.5
V
Operating mode, no load
4.5
0.8
1.0
mA
1
Shutdown Current
I SHDN
SHDN = GND
0.2
Power-Supply Rejection Ratio
PSRR
Measured at DC
70
µA
dB
SHUTDOWN
SHDN Input High
VSDH
SHDN Input Low
VSDL
SHDN Input Leakage Current
4.5
V SHDN = 0 to VDD
V
±0.2
0.5
V
±10
µA
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.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
FILTER CHARACTERISTICS
Corner-Frequency Range
Clock-to-Corner Ratio
fC
(Note 1)
0.001 to 12
fCLK/fC
Clock-to-Corner Tempco
10
Output Voltage Range
Output Offset Voltage
0.25
VOFFSET
DC Insertion Gain with Output
Offset Removed
Total Harmonic Distortion plus
Noise
THD+N
AOS
COM Voltage Range
VCOM
Input Resistance at COM
VIN = VCOM = VDD / 2
VCOM = VDD / 2 (Note 2)
Offset Voltage Gain
Input Voltage Range at OS
kHz
100:1
VOS
V
±4
±25
mV
0.2
0.4
dB
fIN = 200Hz, VIN = 2.5Vp-p,
measurement bandwidth = 22kHz
-79
dB
OS to OUT
+1
V/V
VDD
- 0.1
2
Measured with respect to COM
RCOM
Clock Feedthrough
0
ppm/°C
VDD - 0.25
VDD
2
VDD
+ 0.1
2
V
±0.1
V
90
130
kΩ
3
mVp-p
Resistance Output Load Drive
RL
TA = +25°C
10
1
kΩ
Maximum Capacitive Load
at OUT
CL
50
500
pF
Input Leakage Current at COM
Input Leakage Current at OS
SHDN = GND, VCOM = 0 to VDD
VOS = 0 to VDD
±0.2
±10
µA
±0.2
±10
µA
_______________________________________________________________________________________
3
MAX7426/MAX7427
ELECTRICAL CHARACTERISTICS—MAX7426 (continued)
MAX7426/MAX7427
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
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.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
13.5
17.5
21.5
kHz
±7.5
±12.5
µA
CLOCK
Internal Oscillator Frequency
fOSC
COSC = 1000pF (Note 3)
Clock Output Current
(internal oscillator mode)
ICLK
VCLK = 0 or 3V
Clock Input High
VIH
Clock Input Low
VIL
2.5
V
0.5
V
3.6
V
mA
POWER REQUIREMENTS
Supply Voltage
Supply Current
VDD
IDD
2.7
Operating mode, no load
0.75
1.0
Shutdown Current
I SHDN
SHDN = GND
0.2
1
Power-Supply Rejection Ratio
PSRR
Measured at DC
70
µA
dB
SHUTDOWN
SHDN Input High
VSDH
SHDN Input Low
VSDL
SHDN Input Leakage Current
2.5
V SHDN = 0 to VDD
V
±0.2
0.5
V
±10
µA
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 = VDD / 2, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Note 3)
PARAMETER
Insertion Gain
with DC Gain Error Removed
(Note 4)
MIN
TYP
MAX
fIN = 0.38fC
CONDITIONS
-0.4
-0.2
0.4
fIN = 0.68fC
-0.4
0.2
0.4
fIN = 0.87fC
-0.4
-0.2
0.4
fIN = 0.97fC
-0.4
0.2
0.4
fIN = fC
-0.7
-0.2
0.2
fIN = 1.25fC
-38.5
-34
fIN = 1.43fC
-37.2
-35
fIN = 3.25fC
-37.2
-35
UNITS
dB
Note 1: The maximum fC is defined as the clock frequency fCLK = 100 ✕ fC at which the peak SINAD drops to 68dB with a sinusoidal input at 0.2fC.
Note 2: DC insertion gain is defined as ∆VOUT / ∆VIN.
Note 3: fOSC (kHz) ≈ 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.
4
_______________________________________________________________________________________
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
(VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA = +25°C, unless otherwise noted.)
PASSBAND FREQUENCY RESPONSE
GAIN (dB)
-30
-0.2
-0.4
-40
-0.6
-50
-60
-0.8
-70
-1.0
1
2
3
4
fC = 1kHz
r = 1.25
-150
-200
-250
-300
-350
-400
0
5
-100
INPUT FREQUENCY (kHz)
0.2
0.4
0.6
0.8
1.0
0
0.2
INPUT FREQUENCY (kHz)
0.4
0.6
0.8
1.0
1.2
INPUT FREQUENCY (kHz)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
0.88
MAX7426/27-07
0.82
0.86
0.84
SUPPLY CURRENT (mA)
0.80
0.78
0.76
0.74
MAX7426/27-08
0
SUPPLY CURRENT (mA)
GAIN (dB)
0
-20
fC = 1kHz
r = 1.25
-50
PHASE SHIFT (DEGREES)
0.2
-10
PHASE RESPONSE
0
MAX7426/27-04
MAX7426/27-02
fC = 1kHz
r = 1.25
0
0.4
MAX7426/27-06
FREQUENCY RESPONSE
10
VDD = +5V
0.82
0.80
0.78
0.76
VDD = +3V
0.74
0.72
0.72
0.70
0.70
0.68
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
-60
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX7426/MAX7427
Typical Operating Characteristics
Typical Operating Characteristics (continued)
(VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA = +25°C, unless otherwise noted.)
0
MAX7426/27-10
0
SEE TABLE 1.
-10
-20
THD + NOISE (dB)
-20
-30
-40
-50
-60
-70
SEE TABLE 1.
-10
-30
-40
-50
-60
-70
B
B
-80
-80
A
-90
0
1
2
A
-90
3
4
0
5
0.5
1.0
1.5
2.0
2.5
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
Table 1. THD + Noise Test Conditions
6
MAX7426/27-12
MAX7427
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT SIGNAL AMPLITUDE
MAX7426
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT SIGNAL AMPLITUDE
THD + NOISE (dB)
MAX7426/MAX7427
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
LABEL
fIN
(Hz)
fC
(kHz)
fCLK
(kHz)
MEASUREMENT
BANDWIDTH (kHz)
A
200
1
100
22
B
1k
5
500
80
_______________________________________________________________________________________
3.0
5th-Order, Lowpass, Elliptic,
Switched-Capacitor
(VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA = +25°C, unless otherwise noted.)
INTERNAL OSCILLATOR PERIOD
vs. LARGE CAPACITANCE (IN nF)
INTERNAL OSCILLATOR PERIOD
vs. SMALL CAPACITANCE (IN pF)
150
VDD = +3V
100
50
MAX7426/27-14
18
OSCILLATOR PERIOD (ms)
VDD = +5V
OSCILLATOR PERIOD (µs)
20
MAX7426/27-13
200
VDD = +5V
16
14
12
VDD = +3V
10
8
6
4
2
0
0
500
100
150
200
250
300
350
CAPACITANCE (nF)
INTERNAL OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
INTERNAL OSCILLATOR FREQUENCY
vs. TEMPERATURE
17.3
17.2
MAX7426/27-16
MAX7426/27-15
17.4
18.0
VDD = +3V
17.6
VDD = +5V
17.2
16.8
16.4
COSC = 1000pF
COSC = 1000pF
16.0
17.1
3.0
3.5
4.0
4.5
5.0
-40
5.5
-20
0
20
40
60
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
DC OFFSET VOLTAGE
vs. TEMPERATURE
DC OFFSET VOLTAGE
vs. SUPPLY VOLTAGE
MAX7426/27-17
0
-0.5
-1.0
VDD = +3V
-1.5
-2.0
-2.5
VDD = +5V
-3.0
80
0
100
MAX7426/27-18
2.5
-0.5
DC OFFSET VOLTAGE (mV)
2.0
DC OFFSET VOLTAGE (mV)
50
CAPACITANCE (pF)
17.5
OSCILLATOR FREQUENCY (kHz)
0
1000 1500 2000 2500 3000 3500
OSCILLATOR FREQUENCY (kHz)
0
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
-3.5
-40
-20
0
20
40
60
TEMPERATURE (°C)
80
100
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
7
MAX7426/MAX7427
Typical Operating Characteristics (continued)
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
MAX7426/MAX7427
Pin Description
PIN
NAME
FUNCTION
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.
1
COM
2
IN
3
GND
Ground
4
VDD
Positive Supply Input, +5V for MAX7426 or +3V for MAX7427
5
OUT
Filter Output
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.
7
SHDN
Shutdown Input. Drive low to enable shutdown mode; drive high or connect to VDD for normal operation.
8
CLK
Filter Input
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.
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
RS
+
-
VIN C1
C2
C4
L2
L4
C3
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, 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.
C5
Figure 1. 5th-Order Ladder Elliptic Filter Network
8
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.
RL
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
_______________________________________________________________________________________
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
RIPPLE
0.1µF
VDD
fC
GAIN (dB)
f
TRANSITION RATIO = S
fC
INPUT
IN
SHDN
OUT
COM
OUTPUT
0.1µF
fS
50k
MAX7426
MAX7427
CLOCK
CLK
50k
OS
0.1µF
GND
PASSBAND
50k
STOPBAND
fC
FREQUENCY
fS
Figure 2. Elliptic Filter Response
Figure 3. Offset Adjustment Circuit
powered from 0 to VDD. Varying the rate of the external
clock adjusts the corner frequency of the filter:
Estimate the input impedance of the filter by using the
following formula:
f
fC = CLK
100
Internal Clock
When using the internal oscillator, the capacitance
(COSC) on CLK determines the oscillator frequency:
fOSC (kHz) =
17.5 × 103
COSC (pF)
Since COSC 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.
ZIN =
1
fCLK × CIN
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 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:
VOUT = (VIN − VCOM ) + VOS
V
VCOM = DD (typical)
2
where (VIN - VCOM) is lowpass filtered by the SCF and
OS is added at the output stage. See the Electrical
_______________________________________________________________________________________
9
MAX7426/MAX7427
VSUPPLY
MAX7426/MAX7427
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
For either single-supply or dual-supply operation, drive
CLK and SHDN from GND (V- in dual-supply operation)
to V DD . 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.
V+
VDD
INPUT
IN
SHDN
OUT
COM
*
OUTPUT
Input Signal Amplitude Range
MAX7426
MAX7427
V+
CLOCK
V-
CLK
OS
0.1µF
0.1µF
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.
GND
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.
V*CONNECT SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
Harmonic Distortion
Figure 4. Dual-Supply Operation
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 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. Singlesupply and dual-supply performance are equivalent.
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
TA = +25°C.
Chip Information
TRANSISTOR COUNT: 1457
PROCESS: BiCMOS
Table 2. Typical Harmonic Distortion
FILTER
fCLK
(kHz)
fIN
(Hz)
500
1k
MAX7426
TYPICAL HARMONIC DISTORTION (dB)
2nd
3rd
4th
5th
-71
-73
-90
-82
-88
-86
-92
-88
-87
-86
-90
-90
-90
-87
-90
-90
4
100
200
500
1k
MAX7427
2
100
10
VIN
(Vp-p)
200
______________________________________________________________________________________
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
8LUMAXD.EPS
______________________________________________________________________________________
11
MAX7426/MAX7427
________________________________________________________Package Information
MAX7426/MAX7427
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
PDIPN.EPS
Package Information (continued)
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.
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Printed USA
is a registered trademark of Maxim Integrated Products.