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19-4764; Rev 2; 6/99
8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
General Description
The MAX7400/MAX7403/MAX7404/MAX7407 8th-order, lowpass, elliptic, switched-capacitor filters (SCFs) operate from a single +5V (MAX7400/MAX7403) or +3V (MAX7404/MAX7407) supply. These devices draw 2mA of supply current and allow corner frequencies from 1Hz to 10kHz, making them ideal for low-power antialiasing and post-DAC filtering applications. They feature a shutdown mode that reduces the supply current to 0.2A. 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. o 8th-Order Lowpass Elliptic Filter o Low Noise and Distortion -82dB THD + Noise (MAX7400) o Clock-Tunable Corner Frequency (1Hz to 10kHz) o 100:1 Clock-to-Corner Ratio o Single-Supply Operation +5V (MAX7400/MAX7403) +3V (MAX7404/MAX7407) o Low Power 2mA (Operating Mode) 0.2A (Shutdown Mode) o Available in 8-Pin SO and DIP Packages o Low Output Offset: 5mV
Features
MAX7400/MAX7403/MAX7404/MAX7407
Ordering Information
PART MAX7400CSA MAX7400CPA MAX7400ESA MAX7400EPA TEMP. RANGE 0C to +70C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP
Applications
ADC Anti-Aliasing Post-DAC Filtering CT2 Base Stations Speech Processing Air-Bag Electronics
Ordering Information continued at end of data sheet.
Selector Guide
PART MAX7400 FILTER RESPONSE Elliptic (r = 1.5) Elliptic (r = 1.2) Elliptic (r = 1.5) Elliptic (r = 1.2) OPERATING VOLTAGE (V) +5 +5 +3 +3
Typical Operating Circuit
VSUPPLY 0.1F VDD INPUT IN SHDN OUT OUTPUT
MAX7403 MAX7404 MAX7407
Pin Configuration
TOP VIEW
COM 1 8 7 CLK SHDN OS OUT
CLOCK
CLK
MAX7400 MAX7403 MAX7404 MAX7407
GND
IN 2 COM OS 0.1F GND 3
VDD 4
MAX7400 MAX7403 MAX7404 MAX7407
SO/DIP
6 5
________________________________________________________________ Maxim Integrated Products
1
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7400/MAX7403/MAX7404/MAX7407
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 = +70C) SO (derate 5.88mW/C above +70C) ..........................471mW DIP (derate 9.1mW/C above +70C) ...........................727mW Operating Temperature Ranges MAX740_C_A .....................................................0C to +70C MAX740_E_A ..................................................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
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, 10k || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1F from COM to GND, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at +25C.) PARAMETER FILTER CHARACTERISTICS Corner Frequency Clock-to-Corner Ratio Clock-to-Corner Tempco Output Voltage Range Output Offset Voltage DC Insertion Gain with Output Offset Removed Total Harmonic Distortion plus Noise OS Voltage Gain to OUT Input Voltage Range at OS THD+N AOS VOS Input, COM externally driven COM Voltage Range VCOM Output, COM internally biased Input Resistance at COM Clock Feedthrough Resistive Output Load Drive Maximum Capacitive Load at OUT Input Leakage Current at COM Input Leakage Current at OS CLOCK Internal Oscillator Frequency Clock Input Current Clock Input High Clock Input Low fOSC ICLK VIH VIL COSC = 1000pF (Note 4) VCLK = 0 or 5V VDD - 0.5 0.5 29 38 15 48 30 kHz A V V RL CL SHDN = GND, VCOM = 0 to VDD VOS = 0 to (VDD - 1V) (Note 3) 10 50 RCOM VDD / 2 - 0.5 VDD / 2 - 0.2 75 VOFFSET VIN = VCOM = VDD / 2 VCOM = VDD / 2 (Note 2) fIN = 200Hz, VIN = 4Vp-p, measurement bandwidth = 22kHz MAX7400 MAX7403 -0.1 0.25 5 0.15 -82 -80 1 VCOM 0.1 VDD / 2 VDD / 2 + 0.5 fC fCLK/fC (Note 1) 0.001 to 10 100:1 10 VDD - 0.25 25 0.3 ppm/C V mV dB dB V/V V kHz SYMBOL CONDITIONS MIN TYP MAX UNITS
VDD / 2 VDD / 2 + 0.2 125 10 1 500 0.1 0.1 10 10
V
k mVp-p k pF A A
2
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
ELECTRICAL CHARACTERISTICS--MAX7400/MAX7403 (continued)
(VDD = +5V, filter output measured at OUT, 10k || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1F from COM to GND, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER POWER REQUIREMENTS Supply Voltage Supply Current Shutdown Current Power-Supply Rejection Ratio SHUTDOWN SHDN Input High SHDN Input Low SHDN Input Leakage Current VSDH VSDL V SHDN = 0 to VDD 0.1 VDD - 0.5 0.5 10 V V A VDD IDD I SHDN PSRR Operating mode, no load, IN = OS = COM SHDN = GND, CLK driven from 0 to VDD Measured at DC 4.5 2 0.2 60 5.5 3.5 1 V mA A dB SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX7400/MAX7403/MAX7404/MAX7407
ELECTRICAL CHARACTERISTICS--MAX7404/MAX7407
(VDD = +3V, filter output measured at OUT, 10k || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1F from COM to GND, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER FILTER CHARACTERISTICS Corner Frequency Clock-to-Corner Ratio Clock-to-Corner Tempco Output Voltage Range Output Offset Voltage DC Insertion Gain with Output Offset Removed Total Harmonic Distortion plus Noise OS Voltage Gain to OUT Input Voltage Range at OS COM Voltage Range Input Resistance at COM Clock Feedthrough Resistive Output Load Drive Maximum Capacitive Load at OUT Input Leakage Current at COM Input Leakage Current at OS RL CL SHDN = GND, VCOM = 0 to VDD VOS = 0 to (VDD - 1V) (Note 3) 10 50 THD+N AOS VOS VCOM RCOM COM internally biased or externally driven VDD / 2 - 0.1 75 VOFFSET VIN = VCOM = VDD / 2 VCOM = VDD / 2 (Note 2) fIN = 200Hz, VIN = 2.5Vp-p, measurement bandwidth = 22kHz MAX7404 MAX7407 -0.1 0.25 5 0.1 -79 -77 1 VCOM 0.1 VDD / 2 VDD / 2 + 0.1 125 10 1 500 0.1 0.1 10 10 fC fCLK/fC (Note 1) 0.001 to 10 100:1 10 VDD - 0.25 25 0.3 ppm/C V mV dB dB V/V V V k mVp-p k pF A A kHz SYMBOL CONDITIONS MIN TYP MAX UNITS
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7400/MAX7403/MAX7404/MAX7407
ELECTRICAL CHARACTERISTICS--MAX7404/MAX7407 (continued)
(VDD = +3V, filter output measured at OUT, 10k || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1F from COM to GND, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CLOCK Internal Oscillator Frequency Clock Input Current Clock Input High Clock Input Low POWER REQUIREMENTS Supply Voltage Supply Current Shutdown Current Power-Supply Rejection Ratio SHUTDOWN SHDN Input High SHDN Input Low SHDN Input Leakage Current VSDH VSDL V S HDN = 0 to VDD 0.1 VDD - 0.5 0.5 10 V V A VDD IDD I SHDN PSRR Operating mode, no load, IN = OS = COM SHDN = GND, CLK driven from 0 to VDD Measured at DC 2.7 2 0.2 60 3.6 3.5 1 V mA A dB fOSC ICLK VIH VIL COSC = 1000pF (Note 4) VCLK = 0 or 3V VDD - 0.5 0.5 26 34 15 43 30 kHz A V V SYMBOL CONDITIONS MIN TYP MAX UNITS
ELLIPTIC (r = 1.5) FILTER CHARACTERISTICS--MAX7400/MAX7404
(VDD = +5V for MAX7400, VDD = +3V for MAX7404; filter output measured at OUT; 10k || 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 = +25C.) PARAMETER fIN = 0.371fC fIN = 0.587fC fIN = 0.737fC fIN = 0.868fC Insertion Gain Relative to DC Gain (Note 5) fIN = 0.940fC fIN = 0.988fC fIN = 1.000fC fIN = 1.500fC fIN = 1.601fC fIN = 2.020fC fIN = 4.020fC CONDITIONS MIN -0.20 -0.20 -0.20 -0.20 -0.20 -0.20 -0.20 TYP -0.10 0.02 -0.08 0.06 -0.03 0.09 0.02 -82 -84 -83 -85 MAX 0.20 0.20 0.20 0.20 0.20 0.25 0.25 -75 -78 -78 -78 dB UNITS
4
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
ELLIPTIC (r = 1.2) FILTER CHARACTERISTICS--MAX7403/MAX7407
(VDD = +5V for MAX7403, VDD = +3V for MAX7407; filter output measured at OUT; 10k || 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 = +25C.) PARAMETER fIN = 0.408fC fIN = 0.640fC fIN = 0.784fC fIN = 0.902fC Insertion Gain Relative to DC Gain (Note 5) fIN = 0.956fC fIN = 0.992fC fIN = 1.000fC fIN = 1.200fC fIN = 1.261fC fIN = 1.533fC fIN = 2.875fC CONDITIONS MIN -0.20 -0.20 -0.20 -0.20 -0.20 -0.20 -0.20 TYP -0.11 0.02 -0.06 0.10 0.02 0.14 0.09 -58 -59 -60 -60 MAX 0.20 0.20 0.20 0.20 0.20 0.30 0.30 -50 -54 -54 -54 dB UNITS
MAX7400/MAX7403/MAX7404/MAX7407
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 75A 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 = +25C; unless otherwise noted.)
MAX7400/MAX7404 (r = 1.5) FREQUENCY RESPONSE
MAX7400/03-01
MAX7400/MAX7404 (r = 1.5) PASSBAND FREQUENCY RESPONSE
MAX7400/03-02
MAX7400/MAX7404 (r = 1.5) PHASE RESPONSE
-80 PHASE SHIFT (DEGREES) -160 -240 -320 -400 -480 -560 -640 fC = 1kHz
MAX7400/03-03
20 fC = 1kHz 0 -20 GAIN (dB) -40 -60 -80 -100 -120 0 1 2 3 4 5 INPUT FREQUENCY (kHz)
0.24 fC = 1kHz 0.20 0.16 GAIN (dB) 0.12 0.08 0.04 0 -0.04 -0.08 0 202 404 606 808
0
1010
0
300
600
900
1200
1500
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters 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 = +25C; unless otherwise noted.)
MAX7403/MAX7407 (r = 1.2) FREQUENCY RESPONSE
MAX7400/03 04
MAX7403/MAX7407 (r = 1.2) PASSBAND FREQUENCY RESPONSE
MAX7400/03 05
MAX7403/MAX7407 (r = 1.2) PHASE RESPONSE
fC = 1kHz -80 PHASE SHIFT (DEGREES) -160 -240 -320 -400 -480 -560 -640
MAX7400/03 06
40 fC = 1kHz 20 0 GAIN (dB)
0.32 0.24 0.16 GAIN (dB) 0.08 0 -0.08 -0.16 -0.24 -0.32
fC = 1kHz
0
-20 -40 -60 -80 -100 -120 0 1 2 3 4 5 INPUT FREQUENCY (kHz)
0
202
404
606
808
1010
0
240
480
720
960
1200
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX7400 toc07
SUPPLY CURRENT vs. TEMPERATURE
MAX7400 toc08
OFFSET VOLTAGE vs. SUPPLY VOLTAGE
VIN = VCOM = VDD/2 15 OFFSET VOLTAGE (mV) 10 5 0 -5 -10 -15 -20 MAX7404 MAX7407 MAX7400 MAX7403
MAX7400 toc09
2.5 2.4 2.3 SUPPLY CURRENT (mA) 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 2.5 3.0 3.5 4.0 4.5 5.0 MAX7404 MAX7407 MAX7400 MAX7403 NO LOAD
2.03 NO LOAD 2.02 SUPPLY CURRENT (mA) 2.01 2.00 1.99 1.98 1.97 MAX7404 MAX7407
20
MAX7400 MAX7403
5.5
-40
-20
0
20
40
60
80
100
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
SUPPLY VOLTAGE (V)
OFFSET VOLTAGE vs. TEMPERATURE
MAX7400/03-10
THD PLUS NOISE vs. INPUT SIGNAL AMPLITUDE (MAX7400)
MAX7400/03 11
THD PLUS NOISE vs. INPUT SIGNAL AMPLITUDE AND RESISTIVE LOAD (MAX7400)
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 -90 RL = 500 RL = 1k RL = 10k fIN = 200Hz fC = 1kHz MEASUREMENT BW = 22kHz
MAX7400/03-12
2.0 VIN = VCOM = VDD/2 1.5 OFFSET VOLTAGE (mV)
0 -10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 D B C NO LOAD (SEE TABLE A)
0
1.0
0.5
0
-0.5 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
-90 0 1 2 3 4 5 AMPLITUDE (Vp-p)
0
1
2
3
4
5
AMPLITUDE (Vp-p)
6
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
Typical Operating Characteristics (continued)
(VDD = +5V for MAX7400/MAX7403, VDD = +3V for MAX7404/MAX7407; VCOM = VOS = VDD / 2; SHDN = VDD; fCLK = 100kHz; TA = +25C; unless otherwise noted.)
THD PLUS NOISE vs. INPUT SIGNAL AMPLITUDE (MAX7403)
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 -90 0 1 2 3 4 5 AMPLITUDE (Vp-p) D B C NO LOAD (SEE TABLE A)
MAX7400/03 13
MAX7400/MAX7403/MAX7404/MAX7407
THD PLUS NOISE vs. INPUT SIGNAL AMPLITUDE AND RESISTIVE LOAD (MAX7403)
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 -90 0 1 2 3 4 5 AMPLITUDE (Vp-p) RL = 10k RL = 500 RL = 1k fIN = 200Hz fC = 1kHz MEASUREMENT BW = 22kHz
MAX7400/03 14
0
0
TABLE A. THD PLUS NOISE vs. INPUT SIGNAL AMPLITUDE TEST CONDITIONS
TRACE A B C D fIN (Hz) 2800 2000 1000 200 fC fCLK MEASUREMENT (kHz) (kHz) BANDWIDTH (kHz) 14 10 5 1 1400 1000 500 100 80 80 80 22
THD PLUS NOISE vs. INPUT SIGNAL AMPLITUDE (MAX7404)
MAX7400 toc15
THD PLUS NOISE vs. INPUT SIGNAL AMPLITUDE AND RESISTIVE LOAD (MAX7404)
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 -90 RL = 500 RL = 10k RL = 1k fIN = 200Hz fC = 1kHz MEASUREMENT BW = 22kHz
MAX7400 toc16
0 -10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 -90 0 0.5 1.0 1.5 2.0 2.5 DC B A NO LOAD (SEE TABLE A)
0
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)
MAX 7400 toc17
THD PLUS NOISE vs. INPUT SIGNAL AMPLITUDE AND RESISTIVE LOAD (MAX7407)
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 RL = 500 RL = 1k RL = 10k fIN = 200Hz fC = 1kHz MEASUREMENT BW = 22kHz
MAXX7400 toc18
0 -10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 D -90 0 0.5 1.0 1.5 2.0 2.5 CB A NO LOAD (SEE TABLE A)
0
-90 3.0 0 0.5 1.0 1.5 2.0 2.5 3.0 AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters 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 = +25C; unless otherwise noted.)
INTERNAL OSCILLATOR FREQUENCY vs. COSC CAPACITANCE
MAX7400 toc19
NORMALIZED OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
MAX7400 toc20
NORMALIZED OSCILLATOR FREQUENCY vs. TEMPERATURE
NORMALIZED OSCILLATOR FREQUENCY 1.03 1.02 1.01 1.00 0.99 0.98 0.97 0.96 MAX7404 MAX7407 MAX7400 MAX7403 COSC = 390pF
MAX7400 toC21
10,000 OSCILLATOR FREQUENCY (kHz)
1.20 NORMALIZED OSCILLATOR FREQUENCY 1.15 1.10 1.05 1.00 0.95 0.90 0.85 0.80 2.5 3.0 3.5 4.0 4.5 5.0 MAX7400 MAX7403 MAX7404 MAX7407 COSC = 390pF
1.04
1000
100
10
1
0.1 0.01
0.1
1
10
100
1000
5.5
-40
-20
0
20
40
60
80
100
COSC CAPACITANCE (nF)
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME COM IN GND VDD OUT OS SHDN CLK FUNCTION Common Input. Biased internally at midsupply. Bypass externally to GND with a 0.1F capacitor. To override internal biasing, drive with an external supply. Filter Input Ground Positive Supply Input: +5V for MAX7400/MAX7403, +3V for MAX7404/MAX7407 Filter Output 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.
8
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
Detailed Description
The MAX7400/MAX7403/MAX7404/MAX7407 family of 8th-order, lowpass filters provides sharp rolloff with good stopband rejection. All parts operate with a 100:1 clock-to-corner frequency ratio and a 10kHz maximum corner frequency. These devices accept a single +5V (MAX7400/MAX7403) or +3V (MAX7404/ MAX7407) supply. Figure 1 shows the functional diagram. Most switched-capacitor filters (SFCs) are designed with biquadratic sections. Each section implements two filtering poles, and the sections can be cascaded to produce higher-order filters. The advantage of this approach is ease of design. However, this type of design is highly sensitive to component variations if any section's Q is high. The MAX7400 family uses an alternative approach, which is to emulate a passive network using switched-capacitor integrators with summing and scaling. The passive network can be synthesized using CAD programs or can be found in many filter books. Figure 2 shows a basic 8th-order ladder elliptic filter structure. A switched-capacitor filter that emulates a passive ladder filter retains many of the same advantages. The component sensitivity of a passive ladder filter is low when compared to a cascaded biquadratic design, because each component affects the entire filter shape rather than a single pole-zero pair. In other words, a mismatched component in a biquadratic design has a concentrated error on its respective poles, while the same mismatch in a ladder filter design spreads its error over all poles.
INT CLOCK LOGIC
MAX7400/MAX7403/MAX7404/MAX7407
CLK
8
7 4
SHDN VDD
IN
2 VDD
SCF COM 1
MAX7400 MAX7403 MAX7404 MAX7407
OFFSET ADJ 5 OUT
6
OS
3
GND
BIAS
Figure 1. Functional Diagram
C9
C10
C11
R1 + -
L1 C2
L3 C4
L5 C6
L7 R2 V0
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.
VIN
C8
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.
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9
8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7400/MAX7403/MAX7404/MAX7407
VSUPPLY RIPPLE 0.1F VDD GAIN (dB) f TRANSITION RATIO = S fC fS INPUT IN SHDN OUT COM 0.1F 50k
fC
OUTPUT
CLOCK
CLK
MAX7400 MAX7403 MAX7404 MAX7407
GND
OS 0.1F
50k
50k
PASSBAND fC fS
STOPBAND 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:
fOSC (kHz) = K 10 3 ; COSC in pF COSC
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 () = (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 0.2A (typ) and places the output of the filter into a high-impedance state. For normal operation, drive SHDN high or connect to VDD.
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.
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 0.1F 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
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
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
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.
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.
MAX7400/MAX7403/MAX7404/MAX7407
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 0.1F 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.
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 10k load and an input signal of 4Vp-p (MAX7400/MAX7403) or 2Vp-p (MAX7404/MAX7407), at TA = +25C.
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.
V+
Table 1. Typical Harmonic Distortion
fCLK (kHz) fC (kHz) fIN (Hz) VIN (Vp-p) TYPICAL HARMONIC DISTORTION (dB) 2nd 3rd 4th 5th
OUTPUT
FILTER
VDD INPUT IN SHDN OUT COM *
100 MAX7400 500
1 5 1 5 1 5 1 5
200 4 1000 200 4 1000 200 2 1000 200 2 1000
-89 -82 -89 -86 -89 -77 -93 -88 -88 -81 -91 -87 -84 -80 -90 -91 -85 -82 -85 -86 -85 -81 -86 -84 -85 -82 -85 -86 -86 -84 -85 -86
V+ V-
CLOCK
CLK
MAX7400 MAX7403 MAX7404 MAX7407
GND
100
OS 0.1F 0.1F
MAX7403 500 100 MAX7404 500 100 MAX7407 500
V*DRIVE SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
Figure 5. Dual-Supply Operation
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8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7400/MAX7403/MAX7404/MAX7407
Ordering Information (continued)
PART MAX7403CSA MAX7403CPA MAX7403ESA MAX7403EPA MAX7404CSA MAX7404CPA MAX7404ESA MAX7404EPA MAX7407CSA MAX7407CPA MAX7407ESA MAX7407EPA TEMP. RANGE 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP
Chip Information
TRANSISTOR COUNT: 1116
Package Information
SOICN.EPS
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 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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