Maxim MAX7400CPA 8th-order, lowpass, elliptic, switched-capacitor filter Datasheet

19-4764; Rev 2; 6/99
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
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
Ordering Information
PART
TEMP. RANGE
MAX7400CSA
0°C to +70°C
MAX7400CPA
MAX7400ESA
MAX7400EPA
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
8 SO
8 Plastic DIP
8 SO
8 Plastic DIP
Ordering Information continued at end of data sheet.
Selector Guide
PART
Typical Operating Circuit
PIN-PACKAGE
OPERATING
VOLTAGE (V)
FILTER RESPONSE
MAX7400
Elliptic (r = 1.5)
+5
MAX7403
Elliptic (r = 1.2)
+5
MAX7404
Elliptic (r = 1.5)
+3
MAX7407
Elliptic (r = 1.2)
+3
VSUPPLY
Pin Configuration
0.1µF
VDD
INPUT
IN
SHDN
OUT
TOP VIEW
OUTPUT
COM 1
CLOCK
CLK
MAX7400
MAX7403
MAX7404
MAX7407
GND
IN 2
COM
OS
GND
0.1µF
3
VDD 4
MAX7400
MAX7403
MAX7404
MAX7407
8
CLK
7
SHDN
6
OS
5
OUT
SO/DIP
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
MAX7400/MAX7403/MAX7404/MAX7407
General Description
MAX7400/MAX7403/MAX7404/MAX7407
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
ABSOLUTE MAXIMUM RATINGS
VDD to GND
MAX7400/MAX7403 ..............................................-0.3V to +6V
MAX7404/MAX7407 ..............................................-0.3V to +4V
IN, OUT, COM, OS, CLK ............................-0.3V to (VDD + 0.3V)
SHDN........................................................................-0.3V to +6V
OUT Short-Circuit Duration...................................................1sec
Continuous Power Dissipation (TA = +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
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—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,
fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
FILTER CHARACTERISTICS
Corner Frequency
Clock-to-Corner Ratio
fC
(Note 1)
0.001 to 10
fCLK/fC
Clock-to-Corner Tempco
10
Output Voltage Range
Output Offset Voltage
kHz
100:1
0.25
VOFFSET
DC Insertion Gain with
Output Offset Removed
VIN = VCOM = VDD / 2
VCOM = VDD / 2 (Note 2)
ppm/°C
VDD - 0.25
-0.1
V
±5
±25
mV
0.15
0.3
dB
MAX7400
-82
MAX7403
-80
Total Harmonic Distortion
plus Noise
THD+N
OS Voltage Gain to OUT
AOS
1
V/V
Input Voltage Range at OS
VOS
VCOM ±0.1
V
COM Voltage Range
Input Resistance at COM
fIN = 200Hz, VIN = 4Vp-p,
measurement bandwidth = 22kHz
dB
VDD / 2
+ 0.5
Input, COM externally driven
VDD / 2
- 0.5
VDD / 2
Output, COM internally biased
VDD / 2
- 0.2
VDD / 2
VDD / 2
+ 0.2
VCOM
RCOM
75
Resistive Output Load Drive
RL
10
Maximum Capacitive Load
at OUT
CL
50
Clock Feedthrough
V
125
kΩ
10
mVp-p
1
kΩ
500
pF
Input Leakage Current at COM
SHDN = GND, VCOM = 0 to VDD
±0.1
±10
µA
Input Leakage Current at OS
VOS = 0 to (VDD - 1V) (Note 3)
±0.1
±10
µA
38
48
kHz
±15
±30
µA
CLOCK
Internal Oscillator Frequency
fOSC
COSC = 1000pF (Note 4)
Clock Input Current
ICLK
VCLK = 0 or 5V
Clock Input High
VIH
Clock Input Low
VIL
2
29
VDD - 0.5
_______________________________________________________________________________________
V
0.5
V
8th-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
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
5.5
V
2
3.5
mA
1
POWER REQUIREMENTS
Supply Voltage
VDD
Supply Current
IDD
4.5
Operating mode, no load, IN = OS = COM
Shutdown Current
I SHDN
SHDN = GND, CLK driven from 0 to VDD
0.2
Power-Supply Rejection Ratio
PSRR
Measured at DC
60
µA
dB
SHUTDOWN
SHDN Input High
VSDH
SHDN Input Low
VSDL
SHDN Input Leakage Current
VDD - 0.5
V SHDN = 0 to VDD
V
±0.1
0.5
V
±10
µA
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,
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
fC
Clock-to-Corner Ratio
(Note 1)
0.001 to 10
fCLK/fC
Clock-to-Corner Tempco
10
Output Voltage Range
Output Offset Voltage
kHz
100:1
0.25
VOFFSET
DC Insertion Gain with Output
Offset Removed
VIN = VCOM = VDD / 2
VCOM = VDD / 2 (Note 2)
Total Harmonic Distortion
plus Noise
THD+N
OS Voltage Gain to OUT
AOS
Input Voltage Range at OS
VOS
fIN = 200Hz, VIN = 2.5Vp-p,
measurement bandwidth = 22kHz
-0.1
VDD - 0.25
±25
mV
0.1
0.3
dB
-79
MAX7407
-77
COM Voltage Range
VCOM
COM internally biased or externally driven
Input Resistance at COM
RCOM
75
Resistive Output Load Drive
RL
10
Maximum Capacitive Load
at OUT
CL
50
Clock Feedthrough
V
±5
MAX7404
VDD / 2
- 0.1
ppm/°C
dB
1
V/V
VCOM ±0.1
V
VDD / 2
VDD / 2
+ 0.1
V
125
kΩ
10
mVp-p
1
kΩ
500
pF
Input Leakage Current at COM
SHDN = GND, VCOM = 0 to VDD
±0.1
±10
µA
Input Leakage Current at OS
VOS = 0 to (VDD - 1V) (Note 3)
±0.1
±10
µA
_______________________________________________________________________________________
3
MAX7400/MAX7403/MAX7404/MAX7407
ELECTRICAL CHARACTERISTICS—MAX7400/MAX7403 (continued)
MAX7400/MAX7403/MAX7404/MAX7407
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
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,
fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
34
43
kHz
±15
±30
µA
CLOCK
Internal Oscillator Frequency
fOSC
COSC = 1000pF (Note 4)
Clock Input Current
ICLK
VCLK = 0 or 3V
Clock Input High
VIH
Clock Input Low
VIL
26
VDD - 0.5
V
0.5
V
3.6
V
mA
POWER REQUIREMENTS
Supply Voltage
Supply Current
VDD
IDD
2.7
2
3.5
Shutdown Current
I SHDN
Operating mode, no load, IN = OS = COM
SHDN = GND, CLK driven from 0 to VDD
0.2
1
Power-Supply Rejection Ratio
PSRR
Measured at DC
60
µA
dB
SHUTDOWN
SHDN Input High
VSDH
SHDN Input Low
VSDL
SHDN Input Leakage Current
VDD - 0.5
V S HDN = 0 to VDD
V
±0.1
0.5
V
±10
µA
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;
VCOM = VOS = VDD / 2; fCLK = 100kHz; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
Insertion Gain Relative to DC Gain
(Note 5)
4
CONDITIONS
MIN
TYP
MAX
fIN = 0.371fC
-0.20
-0.10
0.20
fIN = 0.587fC
-0.20
0.02
0.20
fIN = 0.737fC
-0.20
-0.08
0.20
fIN = 0.868fC
-0.20
0.06
0.20
fIN = 0.940fC
-0.20
-0.03
0.20
fIN = 0.988fC
-0.20
0.09
0.25
fIN = 1.000fC
-0.20
0.02
0.25
fIN = 1.500fC
-82
-75
fIN = 1.601fC
-84
-78
fIN = 2.020fC
-83
-78
fIN = 4.020fC
-85
-78
_______________________________________________________________________________________
UNITS
dB
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
(VDD = +5V for MAX7403, VDD = +3V for MAX7407; 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.)
PARAMETER
CONDITIONS
Insertion Gain Relative to DC Gain
(Note 5)
MIN
TYP
MAX
fIN = 0.408fC
-0.20
-0.11
0.20
fIN = 0.640fC
-0.20
0.02
0.20
fIN = 0.784fC
-0.20
-0.06
0.20
fIN = 0.902fC
-0.20
0.10
0.20
fIN = 0.956fC
-0.20
0.02
0.20
fIN = 0.992fC
-0.20
0.14
0.30
fIN = 1.000fC
-0.20
0.09
0.30
fIN = 1.200fC
-58
-50
fIN = 1.261fC
-59
-54
fIN = 1.533fC
-60
-54
fIN = 2.875fC
-60
-54
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: OS voltages above VDD - 1V saturate the input and result in a 75µA typical input leakage current.
Note 4: For MAX7400/MAX7403, fOSC (kHz) ≅ 38 · 103 / COSC (pF). For MAX7404/MAX7407, fOSC (kHz) ≅ 34 · 103 / COSC (pF).
Note 5: The input frequencies, fIN, are selected at the peaks and troughs of the frequency responses.
Typical Operating Characteristics
(VDD = +5V for MAX7400/MAX7403, VDD = +3V for MAX7404/MAX7407; VCOM = VOS = VDD / 2; SHDN = VDD; fCLK = 100kHz;
TA = +25°C; unless otherwise noted.)
MAX7400/MAX7404 (r = 1.5)
PASSBAND FREQUENCY RESPONSE
fC = 1kHz
0
fC = 1kHz
0.20
GAIN (dB)
GAIN (dB)
-40
-60
0.12
0.08
0.04
-80
0
-100
-0.08
0
1
2
3
INPUT FREQUENCY (kHz)
4
5
-160
-240
-320
-400
-480
-560
-0.04
-120
fC = 1kHz
-80
PHASE SHIFT (DEGREES)
0.16
-20
0
MAX7400/03-02
0.24
MAX7400/03-01
20
MAX7400/MAX7404 (r = 1.5)
PHASE RESPONSE
MAX7400/03-03
MAX7400/MAX7404 (r = 1.5)
FREQUENCY RESPONSE
-640
0
202
404
606
INPUT FREQUENCY (Hz)
808
1010
0
300
600
900
1200
1500
INPUT FREQUENCY (Hz)
_______________________________________________________________________________________
5
MAX7400/MAX7403/MAX7404/MAX7407
ELLIPTIC (r = 1.2) FILTER CHARACTERISTICS—MAX7403/MAX7407
Typical Operating Characteristics (continued)
(VDD = +5V for MAX7400/MAX7403, VDD = +3V for MAX7404/MAX7407; VCOM = VOS = VDD / 2; SHDN = VDD; fCLK = 100kHz;
TA = +25°C; unless otherwise noted.)
MAX7403/MAX7407 (r = 1.2)
PASSBAND FREQUENCY RESPONSE
0.24
0.16
-20
0.08
GAIN (dB)
0
-40
-0.08
-80
-0.16
-100
-0.24
-120
fC = 1kHz
-80
1
2
3
4
5
202
404
606
808
1010
0
240
480
720
960
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT
vs. TEMPERATURE
OFFSET VOLTAGE
vs. SUPPLY VOLTAGE
1.9
1.8
2.01
MAX7400
MAX7403
2.00
1.99
3.5
4.0
4.5
5.0
5.5
MAX7400
MAX7403
MAX7404
MAX7407
0
-5
-20
1.97
3.0
5
-15
1.6
1.5
10
-10
MAX7404
MAX7407
1.98
MAX7400 toc09
VIN = VCOM = VDD/2
15
OFFSET VOLTAGE (mV)
2.02
SUPPLY CURRENT (mA)
MAX7400
MAX7403
MAX7404
MAX7407
NO LOAD
1200
20
MAX7400 toc08
MAX7400 toc07
2.03
1.7
-40
-20
0
20
40
60
80
2.5
100
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
OFFSET VOLTAGE vs. TEMPERATURE
THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE (MAX7400)
THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE AND RESISTIVE LOAD (MAX7400)
0.5
-30
-40
-50
B
-60
D
-20
0
20
40
60
TEMPERATURE (°C)
80
100
-30
-40
RL = 500Ω
-50
-60
RL = 1kΩ
-70
RL = 10kΩ
-90
-90
-40
-20
-80
-80
-0.5
fIN = 200Hz
fC = 1kHz
MEASUREMENT BW = 22kHz
C
-70
0
MAX7400/03-12
-20
0
-10
THD + NOISE (dB)
1.0
NO LOAD
(SEE TABLE A)
-10
THD + NOISE (dB)
1.5
0
MAX7400/03 11
VIN = VCOM = VDD/2
MAX7400/03-10
2.0
6
-480
-640
0
2.2
2.5
-400
INPUT FREQUENCY (Hz)
2.3
2.0
-320
INPUT FREQUENCY (Hz)
NO LOAD
2.1
-240
INPUT FREQUENCY (kHz)
2.5
2.4
-160
-560
-0.32
0
SUPPLY CURRENT (mA)
0
-60
0
MAX7400/03 06
20
fC = 1kHz
PHASE SHIFT (DEGREES)
fC = 1kHz
GAIN (dB)
0.32
MAX7400/03 04
40
MAX7403/MAX7407 (r = 1.2)
PHASE RESPONSE
MAX7400/03 05
MAX7403/MAX7407 (r = 1.2)
FREQUENCY RESPONSE
OFFSET VOLTAGE (mV)
MAX7400/MAX7403/MAX7404/MAX7407
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
0
1
2
3
AMPLITUDE (Vp-p)
4
5
0
1
2
3
AMPLITUDE (Vp-p)
_______________________________________________________________________________________
4
5
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE AND RESISTIVE LOAD (MAX7403)
THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE (MAX7403)
-40
-50
B
D
-70
-20
C
-40
-70
-90
3
4
RL = 500Ω
A
2800
14
1400
80
RL = 1kΩ
B
2000
10
1000
80
RL = 10kΩ
C
1000
5
500
80
D
200
1
100
22
-60
-90
2
fIN
(Hz)
-50
-80
1
0
5
1
2
3
4
5
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE AND RESISTIVE LOAD (MAX7404)
THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE (MAX7404)
NO LOAD
(SEE TABLE A)
-30
-40
-50
A
-60
D C
B
fIN = 200Hz
fC = 1kHz
MEASUREMENT BW = 22kHz
-10
-20
THD + NOISE (dB)
-20
0
MAX7400 toc15
0
-10
-30
-40
-60
-70
-70
-80
-80
-90
RL = 500Ω
-50
RL = 10kΩ
RL = 1kΩ
-90
0.5
1.0
1.5
2.0
2.5
3.0
0
0.5
1.0
1.5
2.0
2.5
3.0
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE (MAX7407)
THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE AND RESISTIVE LOAD (MAX7407)
NO LOAD
(SEE TABLE A)
-10
-20
-30
-40
-50
C B
-60
0
A
fIN = 200Hz
fC = 1kHz
MEASUREMENT BW = 22kHz
-10
-20
THD + NOISE (dB)
0
MAX 7400 toc17
0
-30
-40
-50
RL = 500Ω
-60
RL = 1kΩ
RL = 10kΩ
-70
-70
MAXX7400 toc18
THD + NOISE (dB)
fC fCLK MEASUREMENT
(kHz) (kHz) BANDWIDTH (kHz)
TRACE
-30
-80
0
TABLE A. THD PLUS NOISE vs. INPUT SIGNAL
AMPLITUDE TEST CONDITIONS
MAX7400 toc16
-60
fIN = 200Hz
fC = 1kHz
MEASUREMENT BW = 22kHz
-10
THD + NOISE (dB)
-30
THD + NOISE (dB)
THD + NOISE (dB)
-20
MAX7400/03 14
NO LOAD
(SEE TABLE A)
-10
0
MAX7400/03 13
0
-80
-80
D
-90
-90
0
0.5
1.0
1.5
2.0
AMPLITUDE (Vp-p)
2.5
3.0
0
0.5
1.0
1.5
2.0
2.5
3.0
AMPLITUDE (Vp-p)
_______________________________________________________________________________________
7
MAX7400/MAX7403/MAX7404/MAX7407
Typical Operating Characteristics (continued)
(VDD = +5V for MAX7400/MAX7403, VDD = +3V for MAX7404/MAX7407; VCOM = VOS = VDD / 2; SHDN = VDD; fCLK = 100kHz;
TA = +25°C; unless otherwise noted.)
Typical Operating Characteristics (continued)
(VDD = +5V for MAX7400/MAX7403, VDD = +3V for MAX7404/MAX7407; VCOM = VOS = VDD / 2; SHDN = VDD; fCLK = 100kHz;
TA = +25°C; unless otherwise noted.)
10
1
0.1
0.01
1.15
1.10
MAX7404
MAX7407
1.05
1.00
0.95
MAX7400
MAX7403
0.90
0.85
10
100
COSC CAPACITANCE (nF)
1000
COSC = 390pF
1.03
MAX7400
MAX7403
1.02
1.01
1.00
0.99
MAX7404
MAX7407
0.98
0.97
0.96
0.80
1
0.1
1.04
NORMALIZED OSCILLATOR FREQUENCY
100
COSC = 390pF
MAX7400 toc20
1000
1.20
NORMALIZED OSCILLATOR FREQUENCY
MAX7400 toc19
10,000
NORMALIZED OSCILLATOR FREQUENCY
vs. TEMPERATURE
NORMALIZED OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX7400 toC21
INTERNAL OSCILLATOR FREQUENCY
vs. COSC CAPACITANCE
OSCILLATOR FREQUENCY (kHz)
MAX7400/MAX7403/MAX7404/MAX7407
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
-20
SUPPLY VOLTAGE (V)
0
20
40
60
80
100
TEMPERATURE (°C)
Pin Description
8
PIN
NAME
FUNCTION
1
COM
2
IN
3
GND
Ground
4
VDD
Positive Supply Input: +5V for MAX7400/MAX7403, +3V for MAX7404/MAX7407
5
OUT
Filter Output
6
OS
7
SHDN
8
CLK
Common Input. Biased internally at midsupply. Bypass externally to GND with a 0.1µF capacitor. To override internal biasing, drive with an external supply.
Filter Input
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.
Shutdown Input. Drive low to enable shutdown mode; drive high or connect to VDD for normal operation.
Clock Input. To override the internal oscillator, connect to an external clock; otherwise, connect an external
capacitor (COSC) from CLK to GND to set the internal oscillator frequency.
_______________________________________________________________________________________
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
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 PostDAC 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.
INT
CLOCK
8
CLK
7
LOGIC
4
MAX7400/MAX7403/MAX7404/MAX7407
Detailed Description
SHDN
VDD
2
IN
VDD
MAX7400
MAX7403
MAX7404
MAX7407
SCF
1
COM
5
OFFSET
ADJ
6
3
OUT
OS
GND
BIAS
Figure 1. Functional Diagram
C9
R1
+
-
VIN
L3
L1
C2
C4
C10
C11
L5
L7
C6
C8
R2
V0
Figure 2. 8th-Order Ladder Filter Network
The corner frequency, fC, 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 / fC
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.
_______________________________________________________________________________________
9
VSUPPLY
RIPPLE
0.1µF
fC
VDD
f
TRANSITION RATIO = S
fC
GAIN (dB)
MAX7400/MAX7403/MAX7404/MAX7407
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
INPUT
SHDN
OUT
IN
OUTPUT
COM
0.1µF
fS
CLOCK
CLK
MAX7400
MAX7403
MAX7404
MAX7407
50k
OS
0.1µF
GND
PASSBAND
fS
FREQUENCY
Figure 3. Elliptic Filter Response
Figure 4. Offset Adjustment Circuit
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 = fCLK / 100
Internal Clock
When using the internal oscillator, the capacitance
(COSC) on the CLK pin determines the oscillator frequency:
K ⋅ 10 3
; COSC in pF
COSC
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
10
50k
STOPBAND
fC
fOSC (kHz) =
50k
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:
1
ZIN (Ω) =
(fCLK ⋅ CIN )
where fCLK = 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:
VOUT = (VIN - VCOM) + VOS
______________________________________________________________________________________
8th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
Power Supplies
The MAX7400/MAX7403 operate from a single +5V
supply. The MAX7404/MAX7407 operate 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
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 Characteristics 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.
Table 1. Typical Harmonic Distortion
V+
FILTER
VDD
INPUT
V+
V-
CLOCK
IN
CLK
MAX7400
MAX7403
MAX7404
MAX7407
SHDN
OUT
COM
fCLK
(kHz)
fC
(kHz)
fIN
(Hz)
VIN
(Vp-p)
*
TYPICAL
HARMONIC
DISTORTION (dB)
2nd 3rd 4th 5th
OUTPUT
100
1
200
MAX7400
500
5
1000
100
1
200
MAX7403
OS
0.1µF
GND
V-
-89 -82 -89 -86
4
-89 -77 -93 -88
-88 -81 -91 -87
4
500
5
1000
100
1
200
-84 -80 -90 -91
0.1µF
MAX7404
-85 -82 -85 -86
2
500
5
1000
100
1
200
MAX7407
-85 -81 -86 -84
-85 -82 -85 -86
2
500
5
1000
-86 -84 -85 -86
*DRIVE SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
Figure 5. Dual-Supply Operation
______________________________________________________________________________________
11
MAX7400/MAX7403/MAX7404/MAX7407
with VCOM = VDD / 2 (typical), and where (VIN - VCOM)
is lowpass filtered by the SCF, and VOS is 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.
Ordering Information (continued)
PART
TEMP. RANGE
MAX7403CSA
0°C to +70°C
MAX7403CPA
MAX7403ESA
MAX7403EPA
MAX7404CSA
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
8 Plastic DIP
8 SO
8 Plastic DIP
8 SO
MAX7404CPA
MAX7404ESA
MAX7404EPA
MAX7407CSA
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
8 Plastic DIP
8 SO
8 Plastic DIP
8 SO
MAX7407CPA
MAX7407ESA
MAX7407EPA
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
8 Plastic DIP
8 SO
8 Plastic DIP
Chip Information
PIN-PACKAGE
8 SO
TRANSISTOR COUNT: 1116
Package Information
SOICN.EPS
MAX7400/MAX7403/MAX7404/MAX7407
8th-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
© 1999 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.