MAX7424EUA [MAXIM]
5th-Order, Lowpass, Switched-Capacitor Filters; 5阶，低通，开关电容滤波器
| 型号： | MAX7424EUA |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 5th-Order, Lowpass, Switched-Capacitor Filters |
| 文件： | 总14页 (文件大小：407K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1821; Rev 0; 11/00
5th-Order, Lowpass,
Switched-Capacitor Filters
General Description
Features
The MAX7418–MAX7425 5th-order, low-pass, switched-
capacitor filters (SCFs) operate from a single +5V
(MAX7418–MAX7421) or +3V (MAX7422–MAX7425)
supply. These devices draw only 3mA of supply current
and allow corner frequencies from 1Hz to 45kHz, mak-
ing them ideal for low-power post-DAC filtering and anti-
aliasing applications. They feature a shutdown mode
that reduces supply current to 0.2µA.
ꢀ 5th-Order, Lowpass Filters
Elliptic Response (MAX7418/MAX7421/
MAX7422/MAX7425)
Bessel Response (MAX7419/MAX7423)
Butterworth Response (MAX7420/MAX7424)
ꢀ Clock-Turnable Corner Frequency (1Hz to 45kHz)
ꢀ Single-Supply Operation
+5V (MAX7418–MAX7421)
+3V (MAX7422–MAX7425)
Two clocking options are available: self-clocking
(through the use of an external capacitor), or external
clocking for tighter corner-frequency control. An offset
adjust pin allows for adjustment of the DC output level.
ꢀ Low Power
3mA (Operating Mode)
0.2µA (Shutdown Mode)
The MAX7418/MAX7422 deliver 53dB of stopband
rejection and a sharp rolloff with a 1.6 transition ratio.
The MAX7421/MAX7425 achieve a sharper rolloff with a
1.25 transition ratio while still providing 37dB of stop-
band rejection. The MAX7419/MAX7423 Bessel filters
provide low overshoot and fast settling, and the
MAX7420/MAX7424 Butterworth filters provide a maxi-
mally flat passband response. Their fixed response sim-
plifies the design task of selecting a clock frequency.
ꢀ Available in 8-Pin µMAX Package
ꢀ Low Output Offset: 4mV
Ordering Information
PART
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
MAX7418CUA
MAX7418EUA
MAX7419CUA
MAX7419EUA
MAX7420CUA
MAX7420EUA
MAX7421CUA
MAX7421EUA
8 µMAX
8 µMAX
Applications
8 µMAX
ADC Anti-Aliasing
DAC Postfiltering
CT2 Base Stations
8 µMAX
Speech Processing
8 µMAX
8 µMAX
Selector Guide
8 µMAX
OPERATING
VOLTAGE (V)
8 µMAX
PART
FILTER RESPONSE
Ordering Information continued at end of data sheet.
MAX7418
MAX7419
MAX7420
MAX7421
r = 1.6
Bessel
+5
+5
+5
+5
Typical Operating Circuit
Butterworth
r = 1.25
V
SUPPLY
Selector Guide continued at end of data sheet.
0.1µF
Pin Configuration
V
DD
SHDN
OUT
TOP VIEW
INPUT
IN
OUTPUT
COM
IN
1
2
3
4
8
7
6
5
CLK
SHDN
OS
MAX7418–
MAX7425
MAX7418–
MAX7425
CLOCK
CLK
COM
OS
GND
0.1µF
V
DD
OUT
GND
µMAX
________________________________________________________________ Maxim Integrated Products
1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
5th-Order, Lowpass,
Switched-Capacitor Filters
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND..............................................................-0.3V to +6V
Operating Temperature Ranges
IN, OUT, COM, OS, CLK, SHDN ................-0.3V to (V
OUT Short-Circuit Duration.......................................................1s
+ 0.3V)
MAX74 _ _C_A ...................................................0°C to +70°C
MAX74 _ _E_A ................................................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
DD
Continuous Power Dissipation (T = +70°C)
A
8-Pin µMAX (derate 4.1mW/°C above +70°C).............330mW
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—MAX7418–MAX7421
(V
= +5V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND,
DD
SHDN = V , f
= 2.2MHz, T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.)
MAX A
DD CLK
A
MIN
PARAMETER
FILTER CHARACTERISTICS
Corner Frequency
SYMBOL
CONDITIONS
= 4Vp-p (Note 1)
MIN
TYP
MAX
UNITS
f
c
V
0.001 to 30
100:1
kHz
IN
Clock-to-Corner Ratio
Clock-to-Corner Tempco
Output Voltage Range
Output Offset Voltage
f
/ f
CLK C
10
ppm/°C
V
0.25
V
- 0.25
25
DD
V
V
V
= V
= V / 2
4
0.2
0
mV
OFFSET
IN
COM
DD
MAX7418/MAX7421
MAX7419/MAX7420
MAX7418
0
0.4
DC Insertion Gain with
Output Offset Removed
= V / 2
DD
(Note 2)
COM
dB
dB
-0.2
+0.2
-76
-78
-67
-78
1
f
IN
= 2kHz,
= 4Vp-p,
MAX7419
Total Harmonic Distortion
plus Noise
V
IN
THD+N
measurement
bandwidth = 80kHz
MAX7420
MAX7421
Offset Voltage Gain
COM Voltage Range
A
OS
OS to OUT
V/V
V
Input, COM externally driven
Output, COM unconnected
Input, OS externally driven
2.0
2.3
2.5
2.5
3.0
2.7
V
COM
Input Voltage Range at OS
Input Resistance at COM
Clock Feedthrough
V
OS
V
0.1
V
kΩ
COM
R
COM
100
140
5
mVp-p
kΩ
Resistive Output Load Drive
R
L
10
50
1
Maximum Capacitive Output
Load Drive
C
L
500
pF
Input Leakage Current at COM
Input Leakage Current at OS
CLOCK
0.1
0.1
10
10
µA
µA
SHDN = GND, V
= 0 to V
DD
COM
V
OS
= 0 to V
DD
MAX7418/MAX7421
MAX7419/MAX7420
MAX7418/MAX7421
MAX7419/MAX7420
68
86
87
110
40
106
135
60
C
= 1000pF
OSC
Internal Oscillator Frequency
f
kHz
µA
OSC
(Note 3)
V = 0 or 5V
CLK
Clock Output Current
(Internal Oscillator Mode)
I
CLK
50
75
Clock Input High
Clock Input Low
V
4.5
V
V
IH
V
0.5
IL
2
_______________________________________________________________________________________
5th-Order, Lowpass,
Switched-Capacitor Filters
ELECTRICAL CHARACTERISTICS—MAX7418–MAX7421 (continued)
(V
= +5V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND,
DD
SHDN = V , f
= 2.2MHz, T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.)
MAX A
DD CLK
A
MIN
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
POWER REQUIREMENTS
Supply Voltage
V
4.5
5.5
3.6
4.1
1
V
DD
MAX7418/MAX7421
MAX7419/MAX7420
2.9
3.4
0.2
70
Operating mode,
no load
Supply Current
I
mA
DD
Shutdown Current
I
µA
dB
SHDN = GND
SHDN
Power-Supply Rejection Ratio
PSRR
IN = COM (Note 4)
SHUTDOWN
V
4.5
V
V
SHDN Input High
SDH
V
0.5
10
SHDN Input Low
SDL
0.2
µA
SHDN Input Leakage Current
V
= 0 to V
DD
SHDN
ELECTRICAL CHARACTERISTICS—MAX7422–MAX7425
(V
= +3V, filter output measured at OUT pin, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND,
DD
SHDN = V , f
= 2.2MHz, T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.)
MAX A
DD CLK
A
MIN
PARAMETER
SYMBOL
CONDITIONS
MAX7422/MAX7425
= 2.5Vp-p
MIN
TYP
MAX
UNITS
FILTER CHARACTERISTICS
0.001 to 45
V
IN
Corner-Frequency Range
f
C
kHz
(Note 1)
MAX7423/MAX7424
Clock-to-Corner Ratio
Clock-to-Corner Tempco
Output Voltage Range
Output Offset Voltage
f
/f
100:1
10
V
CLK C
ppm/°C
V
0.25
- 0.25
25
DD
V
V
V
= V
= V / 2
4
mV
OFFSET
IN
COM
DD
MAX7422/MAX7425
MAX7423/MAX7424
MAX7422
0
0.2
0
0.4
DC Insertion Gain with Output
Offset Removed
= V / 2
DD
COM
dB
dB
(Note 2)
-0.2
+0.2
-80
-81
-70
-80
1
f
IN
= 2kHz,
= 2.5Vp-p,
MAX7423
Total Harmonic Distortion plus
Noise
V
IN
THD+N
measurement
bandwidth = 80kHz
MAX7424
MAX7425
Offset Voltage Gain
COM Voltage Range
A
OS to OUT
V/V
V
OS
Input, COM externally driven
Output, COM internally driven
Measured with respect to COM
1.4
1.4
1.5
1.5
1.6
1.6
V
COM
Input Voltage Range at OS
Input Resistance at COM
Clock Feedthrough
V
V
0.1
V
kΩ
OS
COM
R
100
140
COM
3
1
mVp-p
kΩ
Resistive Output Load Drive
R
10
50
L
Maximum Capacitive Load
at OUT
C
500
pF
L
Input Leakage Current at COM
Input Leakage Current at OS
0.1
0.1
10
10
µA
µA
SHDN = GND, V
= 0 to V
DD
COM
V
OS
= 0 to V
DD
_______________________________________________________________________________________
3
5th-Order, Lowpass,
Switched-Capacitor Filters
ELECTRICAL CHARACTERISTICS—MAX7422–MAX7425 (continued)
(V
= +3V, filter output measured at OUT pin, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND,
DD
SHDN = V , f
= 2.2MHz, T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.)
MAX A
DD CLK
A
MIN
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
106
UNITS
CLOCK
MAX7422/MAX7425
68
86
68
86
2.5
87
110
87
C
= 1000pF
OSC
Internal Oscillator Frequency
f
kHz
kHz
OSC
(Note 3)
MAX7423/MAX7424
MAX7422/MAX7425
MAX7423/MAX7424
135
106
135
Clock Output Current (Internal
Oscillator Mode)
I
CLK
110
Clock Input High
V
IH
V
V
Clock Input Low
V
IL
0.5
POWER REQUIREMENTS
Supply Voltage
V
2.7
3.6
3.4
3.8
1
V
DD
MAX7422/MAX7425
MAX7423/MAX7424
2.6
3.0
0.2
70
Operating mode,
no load
Supply Current
I
mA
DD
Shutdown Current
I
µA
dB
SHDN = GND
SHDN
Power-Supply Rejection Ratio
SHUTDOWN
PSRR
Measured at DC
V
2.5
V
V
SHDN Input High
SDH
V
0.5
10
SHDN Input Low
SDL
V
= 0 to V
0.2
µA
SHDN Input Leakage Current
DD
SHDN
FILTER CHARACTERISTICS
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425 filter output measured at OUT, 10kΩ || 50pF load to GND at
DD
DD
OUT, SHDN = V , f
= 2.2MHz, T = T
to T , unless otherwise noted.)
MAX
DD CLK
A
MIN
PARAMETER
ELLIPTIC, r = 1.2—MAX7421/MAX7425
CONDITIONS
MIN
TYP
MAX
UNITS
f
IN
f
IN
f
IN
f
IN
f
IN
f
IN
f
IN
f
IN
= 0.38f
= 0.68f
= 0.87f
= 0.97f
-0.4
-0.4
-0.4
-0.4
-0.7
0.2
0.2
0.4
0.4
0.4
0.4
0.2
-33
-35
-35
C
C
C
C
0.2
0.2
Insertion Gain with DC Gain
Error Removed (Note 4)
dB
= f
0.2
C
= 1.25f
= 1.43f
= 3.25f
-36
C
C
C
-37.2
-37.2
BESSEL FILTERS—MAX7419/MAX7423
f
IN
f
IN
f
IN
f
IN
= 0.5f
-1
-0.74
-3.0
C
= f
-3.6
-2.4
-35
-60
C
Insertion Gain Relative to
DC Gain
dB
= 4f
= 7f
-41.0
-67
C
C
4
_______________________________________________________________________________________
5th-Order, Lowpass,
Switched-Capacitor Filters
FILTER CHARACTERISTICS
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425 filter output measured at OUT, 10kΩ || 50pF load to GND at
DD
DD
OUT, SHDN = V , f
= 2.2MHz, T = T
to T , unless otherwise noted.)
MAX
DD CLK
A
MIN
PARAMETER
BUTTERWORTH FILTERS—MAX7420/MAX7424
CONDITIONS
MIN
TYP
MAX
UNITS
f
= 0.5f
-0.3
-3.6
0
IN
IN
IN
C
f
f
= f
-3.0
-47.5
-70
-2.4
-43
-65
C
Insertion Gain Relative to
DC Gain
dB
= 3f
= 5f
C
f
IN
C
Note 1: The maximum f is defined as the clock frequency f
= 100 x f at which the peak S / (THD+N) drops to 68dB with a
C
C
CLK
sinusoidal input at 0.2f . Maximum f increases as V signal amplitude decreases.
C
C
IN
Note 2: DC insertion gain is defined as ∆V
/ ∆V .
OUT
IN
3
Note 3: MAX7418/MAX7421/MAX7422/MAX7425: f
(kHz) ≅ 87x10 / C
(pF).
(pF).
OSC
of 5.5V.
OSC
OSC
OSC
3
MAX7419/MAX7420/MAX7423/MAX7424: f
Note 4: PSRR is the change in output voltage from a V
(kHz) ≅ 110x10 / C
of 4.5V and a V
DD
DD
__________________________________________Typical Operating Characteristics
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425, f
= 2.2MHz, SHDN = V , V
= V = V / 2,
COM OS
DD
CLK
DD
DD
DD
T
A
= +25°C, unless otherwise noted.)
MAX7419/MAX7423
FREQUENCY RESPONSE (BESSEL)
MAX7418/MAX7422
FREQUENCY RESPONSE (ELLIPTIC, r = 1.6)
MAX7420/MAX7424
FREQUENCY RESPONSE (BUTTERWORTH)
10
0
10
0
10
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-10
-20
-30
-40
-50
-60
0
20
40
60
80
100
0
20
40
60
80
100
0
20
40
60
80
100
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
_______________________________________________________________________________________
5
5th-Order, Lowpass,
Switched-Capacitor Filters
____________________________Typical Operating Characteristics (continued)
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425, f
= 2.2MHz, SHDN = V , V
= V = V / 2,
OS
DD
CLK
COM
DD
DD
DD
T
A
= +25°C, unless otherwise noted.
MAX7419/MAX7423
PASSBAND FREQUENCY RESPONSE
(BESSEL)
MAX7418/MAX7422
PASSBAND FREQUENCY RESPONSE
(ELLIPTIC, r = 1.6)
MAX7421/MAX7425
FREQUENCY RESPONSE (ELLIPTIC, r = 1.25)
10
0.5
0
0.4
0.2
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
0
-0.2
-0.4
-0.6
-0.8
-1.0
0
4.5
9.0
13.5
18.0
22.5
0
20
40
60
80
100
0
4.5
9.0
13.5
18.0
22.5
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
MAX7421/MAX7425
PASSBAND FREQUENCY RESPONSE
(ELLIPTIC, r = 1.25)
MAX7420/MAX7424
PASSBAND FREQUENCY RESPONSE
(BUTTERWORTH)
MAX7418/MAX7422
PHASE RESPONSE (ELLIPTIC, r = 1.6)
0
-50
0.5
0
0.4
0.2
-100
-150
-200
-250
-300
-350
-400
-450
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
0
-0.2
-0.4
-0.6
-0.8
-1.0
0
4
8
12
16
20
24
28
0
4.5
9.0
13.5
18.0
22.5
0
4.5
9.0
13.5
18.0
22.5
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
MAX7419/MAX7423
PHASE RESPONSE (BESSEL)
MAX7424/MAX7425
PHASE RESPONSE (ELLIPTIC, r = 1.25)
MAX7420/MAX7424
PHASE RESPONSE (BUTTERWORTH)
0
-50
0
-50
0
-50
-100
-150
-200
-250
-300
-350
-400
-450
-100
-150
-200
-250
-300
-350
-100
-150
-200
-250
0
4
8
12
16
20
24
28
0
4
8
12
16
20
24
28
0
4
8
12
16
20
24
28
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
6
_______________________________________________________________________________________
5th-Order, Lowpass,
Switched-Capacitor Filters
____________________________Typical Operating Characteristics (continued)
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425, f
= 2.2MHz, SHDN = V , V
= V = V / 2,
COM OS
DD
CLK
DD
DD
DD
T
A
= +25°C, unless otherwise noted.
MAX7419
MAX7418
MAX7420
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(ELLIPTIC, r = 1.6)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(BESSEL)
(BUTTERWORTH)
0
0
0
SEE TABLE A
SEE TABLE A
SEE TABLE A
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
D
D
D
E
1
E
3
E
1
0
2
3
4
5
0
2
3
4
5
0
1
2
4
5
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
MAX7421
MAX7423
MAX7422
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(ELLIPTIC, r = 1.25)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(BESSEL)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(ELLIPTIC, r = 1.6)
0
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
0
SEE TABLE A
SEE TABLE A
SEE TABLE A
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
A
A
D
B
B
C
C
E
1
0
0.5
1.0
1.5
2.0
2.5
3.0
0
2
3
4
5
0
0.5
1.0
1.5
2.0
2.5
3.0
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
MAX7424
MAX7425
INTERNAL OSCILLATOR FREQUENCY
vs. SMALL CAPACITANCE (pF)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(BUTTERWORTH)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(ELLIPTIC, r = 1.25)
0
0
7000
6000
5000
4000
3000
2000
1000
0
SEE TABLE A
SEE TABLE A
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
BESSEL/BUTTERWORTH
ELLIPTIC
A
B
A
B
C
C
1
10
100
1000
10000
0
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
CAPACITANCE ( pF)
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
_______________________________________________________________________________________
7
5th-Order, Lowpass,
Switched-Capacitor Filters
____________________________Typical Operating Characteristics (continued)
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425, f
= 2.2MHz, SHDN = V , V
= V = V / 2,
COM OS
DD
CLK
DD
DD
DD
T
A
= +25°C, unless otherwise noted.
ELLIPTIC INTERNAL OSCILLATOR
FREQUENCY vs. SUPPLY VOLTAGE
INTERNAL OSCILLATOR FREQUENCY
vs. LARGE CAPACITANCE (nF)
87.0
86.5
86.0
85.5
85.0
84.5
84.0
6
5
4
3
2
1
0
BESSEL/BUTTERWORTH
ELLIPTIC
C
= 1000PF
OSC
2.5
3.0
3.5
4.0
4.5
5.0
5.5
10
100
1000
SUPPLY VOLTAGE (V)
CAPACITANCE (nF)
ELLIPTIC SUPPLY CURRENT
vs. SUPPLY VOLTAGE
ELLIPTIC INTERNAL OSCILLATOR
FREQUENCY vs. TEMPERATURE
3.3
3.1
2.9
2.7
2.5
2.3
87.0
86.5
86.0
85.5
85.0
84.5
84.0
V
DD
= 3V
V
DD
= 5V
35
C
= 1000pF
-15
OSC
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
10
60
85
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
ELLIPTIC SUPPLY CURRENT
vs. TEMPERATURE
3.0
2.9
2.8
2.7
2.6
2.5
Table A.
f
f
f
BW
IN
C
CLK
LABEL
V
= 5V
= 3V
DD
DD
(kHz) (kHz) (kHz) (kHz)
A
B
C
D
E
2
2
1
2
1
30
22
10
22
10
3000
2200
1000
2200
1000
80
80
22
80
22
V
-40
-15
10
35
60
85
TEMPERATURE (°C)
8
_______________________________________________________________________________________
5th-Order, Lowpass,
Switched-Capacitor Filters
Typical Operating Characteristics (continued)
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425, f
= 2.2MHz, SHDN = V , V
= V = V / 2,
COM OS
DD
CLK
DD
DD
DD
T
A
= +25°C, unless otherwise noted.
DC OFFSET VOLTAGE
vs. SUPPLY VOLTAGE
DC OFFSET VOLTAGE
vs. TEMPERATURE
2.5
3.0
2.5
2.0
1.5
1.0
0.5
0
2.0
1.5
1.0
0.5
0
V
= 5V
DD
V
= 3V
DD
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
-15
10
35
60
85
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
Pin Description
PIN
NAME
FUNCTION
Common Input Pin. Biased internally at midsupply. Bypass COM externally to GND with a 0.1µF capacitor.
To override internal biasing, drive COM with an external supply.
1
COM
2
3
IN
Filter Input
Ground
GND
Positive Supply Input: +5V for MAX7418–MAX7421, +3V for MAX7422–MAX7425. Bypass V to GND with
DD
a 0.1µF capacitor.
4
5
V
DD
OUT
OS
Filter Output
Offset Adjust Input. To adjust output offset, connect OS to an external supply through a resistive voltage-
divider (Figure 4). Connect OS to COM if no offset adjustment is needed. See the Offset and Common-Mode
Input Adjustment section.
6
7
8
Shutdown Input. Drive low to enable shutdown mode; drive high or connect to V
for normal operation.
SHDN
DD
Clock Input. Connect an external capacitor (C
) from CLK to ground. To override the internal oscillator,
OSC
CLK
connect CLK to an external clock: f = f
/100.
C
CLK
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 MAX7418–MAX7425 use an
alternative approach, which is to emulate a passive net-
work using switched-capacitor integrators with sum-
ming 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 lad-
der filter structure.
_______________Detailed Description
The MAX7418/MAX7421/MAX7422/MAX7425 elliptic
lowpass filters provide sharp rolloff with good stopband
rejection. The MAX7419/MAX7423 Bessel filters provide
low overshoot and fast settling responses, and the
MAX7420/MAX7424 Butterworth filters provide a maxi-
mally flat passband response. All parts operate with a
100:1 clock-to-corner frequency ratio.
Most switch capacitor filters (SCFs) are designed with
biquadratic sections. Each section implements two
pole-zero pairs, and the sections can be cascaded to
_______________________________________________________________________________________
9
5th-Order, Lowpass,
Switched-Capacitor Filters
delay all frequency components equally, preserving the
line up shape of step inputs (subject to the attenuation
of the higher frequencies). Bessel filters settle quickly—
an important characteristic in applications that use a
multiplexer (mux) to select an input signal for an ana-
log-to-digital converter (ADC). An anti-aliasing filter
placed between the mux and the ADC must settle
quickly after a new channel is selected.
R
S
L2
L4
+
-
C1
V
IN
C3
C5
R
L
Butterworth Characteristics
Lowpass Butterworth filters such as the MAX7420/
MAX7424 provide a maximally flat passband response,
making them ideal for instrumentation applications that
require minimum deviation from the DC gain throughout
the passband.
Figure 1. 5th-Order Ladder Filter Network
An SCF that emulates a passive ladder filter retains
many of the same advantages. The component sensi-
tivity of a passive ladder filter is low when compared to
a cascaded biquadratic design because each compo-
nent affects the entire filter shape rather than a single
pole-zero pair. In other words, a mismatched compo-
nent 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.
The difference between Bessel and Butterworth filters
can be observed when a 1kHz square wave is applied
to the filter input (Figure 3, trace A). With the filter cutoff
frequencies set at 5kHz, trace B shows the Bessel filter
response and trace C shows the Butterworth filter
response.
Clock Signal
Elliptic Characteristics
Lowpass elliptic filters such as the MAX7418/MAX7421/
MAX7422/MAX7425 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 Anti-Aliasing and Post-DAC
Filtering).
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
powered from 0 to V . Varying the rate of the external
DD
clock adjusts the corner frequency of the filter:
f
CLK
f
=
C
100
In the frequency domain, the first transmission zero
causes the filter’s amplitude to drop to a minimum level
(Figure 2). Beyond this zero, the response rises as the
frequency increases until the next transmission zero.
RIPPLE
The stopband begins at the stopband frequency, f . At
S
frequencies above f , the filter’s gain does not exceed
S
f
C
the gain at f . The corner frequency, f , is defined as
S
C
f
C
S
TRANSITION RATIO =
the point at which 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:
f
f
S
r = f / f
S
C
The MAX7418/MAX7422 have a transition ratio of 1.6
and typically 53dB of stopband rejection. The
MAX7421/MAX7425 have a transition ratio of 1.25 (pro-
viding a steeper rolloff) and typically 37dB of stopband
rejection.
PASSBAND
STOPBAND
FREQUENCY
f
C
f
S
Bessel Characteristics
Lowpass Bessel filters such as the MAX7419/MAX7423
Figure 2. Elliptic Filter Response
10 ______________________________________________________________________________________
5th-Order, Lowpass,
Switched-Capacitor Filters
V
SUPPLY
0.1µF
2V/div
V
DD
SHDN
OUT
A
B
C
OUTPUT
INPUT
IN
COM
2V/div
2V/div
0.1µF
0.1µF
50k
MAX7418–
MAX7425
50k
50k
CLOCK
CLK
OS
GND
200µs/div
A: 1kHz INPUT SIGNAL
B: MAX7419 BESSEL FILTER RESPONSE; f = 5kHz
C
C: MAX7420 BUTTERWORTH FILTER RESPONSE; f = 5kHz
C
Figure 4. Offset Adjustment Circuit
Figure 3. Bessel vs. Butterworth Filter Response
1
Z
=
Internal Clock
When using the internal oscillator, the capacitance
IN
(f
× C )
IN
CLK
(C
) on CLK determines the oscillator frequency:
OSC
where f
= clock frequency and C = 1pF.
IN
CLK
k
Low-Power Shutdown Mode
f
(kHz) =
OSC
C
(pF)
OSC
The MAX7418–MAX7425 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-
where
k = 87 x 103 for the
tion, drive SHDN high or connect to V
.
DD
MAX7418/MAX7421/MAX7422/MAX7425
and
Applications Information
Offset (OS) and Common-Mode (COM)
Input Adjustment
k = 110 x 103 for the
MAX7419/MAX7420/MAX7423/ MAX7424.
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 in which offset
adjustment is required, apply an external bias voltage
through a resistor-divider network to OS, as shown in
Figure 4. 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:
Since C
is in the low picofarads, minimize the stray
OSC
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 2.2MHz produces a
nominal corner frequency of 2.2kHz.
Input Impedance vs. Clock Frequencies
The MAX7418–MAX7425s’ input impedance is effective
as a switched-capacitor resistor and is inversely propor-
tional to frequency. The input impedance values deter-
mined by the equation represents 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.
V
= (V − V
) + V
OUT
IN
COM OS
V
DD
2
V
=
(typ)
COM
where (V - V
) is lowpass filtered by the SCF and
COM
IN
OS is added at the output stage. See the Electrical
Characteristics table for the input voltage range of COM
Estimate the input impedance of the filter by using the
following formula:
______________________________________________________________________________________ 11
5th-Order, Lowpass,
Switched-Capacitor Filters
and OS. Changing the voltage on COM or OS signifi-
cantly from midsupply reduces the dynamic range.
V+
Power Supplies
The MAX7418–MAX7421 operate from a single +5V
supply and the MAX7422–MAX7425 operate from a sin-
*
V
DD
SHDN
OUT
OUTPUT
gle +3V supply. Bypass V
to GND with a 0.1µF
DD
INPUT
IN
COM
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.
Single-supply and dual-supply performance are equiv-
alent. For either single-supply or dual-supply operation,
drive CLK and SHDN from GND (V- in dual supply
MAX7418–
MAX7425
V+
V-
CLOCK
CLK
OS
0.1µF
0.1µF
operation) to V . Use the MAX7418–MAX7421 for
DD
GND
V-
2.5, and use the MAX7422–MAX7425 for 1.5V. For
5V dual-supply applications, refer to the MAX291/
MAX292/MAX295/MAX296 and MAX293/MAX294/
MAX297 data sheets.
*CONNECT SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
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.
Figure 5. Dual-Supply Operation
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. Tables 1, 2,
and 3 list typical harmonic distortion values with a 10kΩ
load at T = +25°C.
A
Anti-Aliasing and Post-DAC Filtering
When using the MAX7418–MAX7425 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.
Table 1. MAX7418/MAX7421/MAX7422/MAX7425 Typical Harmonic Distortion
TYPICAL HARMONIC DISTORTION (dB)
f
f
V
IN
(Vp-p)
CLK
IN
FILTER
MAX7418
MAX7421
MAX7422
MAX7425
(MHz)
(kHz)
2nd
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
3rd
4th
5th
2.2
1.5
2.2
1.5
4.0
2.2
4.0
2.2
2
2
2
2
4
2
4
2
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
4
4
2
2
12 ______________________________________________________________________________________
5th-Order, Lowpass,
Switched-Capacitor Filters
Table 2. MAX7420/MAX7424 Typical Harmonic Distortion
TYPICAL HARMONIC DISTORTION (dB)
f
f
V
IN
(Vp-p)
CLK
IN
FILTER
MAX7420
MAX7424
(MHz)
(kHz)
2nd
-77
3rd
-67
-70
-70
-77
4th
5th
-76
2.2
1.5
3.5
2.2
2
2
3
2
< -80
< -80
< -80
< -80
4
< -80
< -80
< -80
< -80
< -80
< -80
2
Table 3. MAX7419/MAX7423 Typical Harmonic Distortion
TYPICAL HARMONIC DISTORTION (dB)
f
f
V
IN
(Vp-p)
CLK
IN
FILTER
MAX7419
MAX7423
(MHz)
(kHz)
2nd
3rd
-77
4th
5th
2.2
1.5
3.5
2.2
2
2
3
2
< -80
< -80
< -80
< -80
< -80
< -80
< -80
< -80
< -80
< -80
< -80
< -80
4
-80
-75
2
< -80
Ordering Information (continued)
Selector Guide (continued)
PART
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
8 µMAX
OPERATING
FILTER RESPONSE
PART
VOLTAGE (V)
MAX7422CUA
MAX7422EUA
MAX7423CUA
MAX7423EUA
MAX7424CUA
MAX7424EUA
MAX7425CUA
MAX7425EUA
8 µMAX
MAX7422
MAX7423
MAX7424
MAX7425
r = 1.6
Bessel
+3
+3
+3
+3
8 µMAX
8 µMAX
Butterworth
r = 1.25
8 µMAX
8 µMAX
8 µMAX
Chip Information
8 µMAX
TRANSISTOR COUNT: 1457
PROCESS: BiCMOS
______________________________________________________________________________________ 13
5th-Order, Lowpass,
Switched-Capacitor Filters
________________________________________________________Package Information
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2000 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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