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19-1378; Rev 1; 10/98
5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
General Description
The MAX7408/MAX7411/MAX7412/MAX7415 5th-order, lowpass, elliptic, switched-capacitor filters (SCFs) operate from a single +5V (MAX7408/MAX7411) or +3V (MAX7412/MAX7415) supply. The devices draw only 1.2mA of supply current and allow corner frequencies from 1Hz to 15kHz, 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 0.2A. 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 MAX7408/MAX7412 deliver 53dB of stopband rejection and a sharp rolloff with a transition ratio of 1.6. The MAX7411/MAX7415 achieve a sharper rolloff with a transition ratio of 1.25 while still providing 37dB of stopband rejection. Their fixed response limits the design task to selecting a clock frequency. o 5th-Order, Elliptic Lowpass Filters o Low Noise and Distortion: -80dB THD + Noise o Clock-Tunable Corner Frequency (1Hz to 15kHz) o Single-Supply Operation +5V (MAX7408/MAX7411) +3V (MAX7412/MAX7415) o Low Power 1.2mA (operating mode) 0.2A (shutdown mode) o Available in 8-Pin MAX/DIP Packages o Low Output Offset: 4mV
Features
MAX7408/MAX7411/MAX7412/MAX7415
Ordering Information
PART MAX7408CPA MAX7408CUA MAX7408EPA MAX7408EUA MAX7411CPA MAX7411CUA MAX7411EPA MAX7411EUA MAX7412CPA MAX7412CUA MAX7412EPA MAX7412EUA MAX7415CPA MAX7415CUA MAX7415EPA MAX7415EUA 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 0C to +70C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE 8 Plastic DIP 8 MAX 8 Plastic DIP 8 MAX 8 Plastic DIP 8 MAX 8 Plastic DIP 8 MAX 8 Plastic DIP 8 MAX 8 Plastic DIP 8 MAX 8 Plastic DIP 8 MAX 8 Plastic DIP 8 MAX
Applications
ADC Anti-Aliasing Post-DAC Filtering CT2 Base Stations Speech Processing
Selector Guide
PART MAX7408 MAX7411 MAX7412 MAX7415 TRANSITION RATIO r = 1.6 r = 1.25 r = 1.6 r = 1.25 OPERATING VOLTAGE (V) +5 +5 +3 +3
Typical Operating Circuit
VSUPPLY 0.1F VDD INPUT IN SHDN OUT OUTPUT
Pin Configuration
TOP VIEW
COM IN COM OS 0.1F GND 1 2 3 8 7 CLK SHDN OS OUT
CLOCK
CLK
MAX7408 MAX7411 MAX7412 MAX7415
GND
VDD 4
MAX7408 MAX7411 MAX7412 MAX7415
MAX/DIP
6 5
________________________________________________________________ Maxim Integrated Products
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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7408/MAX7411/MAX7412/MAX7415
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...................................................1sec Continuous Power Dissipation (TA = +70C) 8-Pin DIP (derate 6.90mW/C above +70C) ...............552mW 8-Pin MAX (derate 4.1mW/C above +70C) .............330mW Operating Temperature Ranges MAX74_ _C_A .....................................................0C to +70C MAX74_ _E_A ..................................................-40C to +85C Storage Temperature Range .............................-65C to +160C 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--MAX7408/MAX7411
(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 FILTER Corner-Frequency Range 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 Offset Voltage Gain THD+N AOS VOFFSET VIN = VCOM = VDD / 2 VCOM = VDD / 2 (Note 2) fIN = 200Hz, VIN = 4Vp-p, measurement bandwidth = 22kHz OS to OUT Input, COM externally driven COM Voltage Range VCOM Output, COM internally driven Input Voltage Range at OS 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 Output Current (Internal Oscillator Mode) Clock Input High Clock Input Low fOSC ICLK VIH VIL 4.5 0.5 COSC = 1000pF (Note 3) 19 27 12 34 20 kHz A V V RL CL SHDN = GND, VCOM = 0 to VDD VOS = 0 to VDD VOS RCOM TA = +25C 10 50 Measured with respect to COM 110 VDD - 0.5 2 VDD - 0.2 2 0 0.25 4 0.2 -81 1 VDD 2 VDD 2 0.1 180 5 1 500 0.2 0.2 10 10 VDD + 0.5 2 V VDD + 0.2 2 V k mVp-p k pF A A fC fCLK/fC (Note 1) 0.001 to 15 100:1 10 VDD - 0.25 25 0.4 ppm/C V mV dB dB V/V kHz SYMBOL CONDITIONS MIN TYP MAX UNITS
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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
ELECTRICAL CHARACTERISTICS--MAX7408/MAX7411 (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 VSHDN = 0 to VDD 0.2 4.5 0.5 10 V V A VDD IDD I SHDN PSRR Operating mode, no load SHDN = GND Measured at DC 4.5 1.16 0.2 70 5.5 1.5 1 V mA A dB SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX7408/MAX7411/MAX7412/MAX7415
ELECTRICAL CHARACTERISTICS--MAX7412/MAX7415
(VDD = +3V, filter output measured at OUT pin, 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 Range 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 Offset Voltage Gain COM Voltage Range Input Voltage Range at OS Input Resistance at COM Clock Feedthrough Resistance 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 THD+N AOS VCOM VOS RCOM TA = +25C 10 50 Measured with respect to COM 110 VOFFSET VIN = VCOM = VDD / 2 VCOM = VDD / 2 (Note 2) fIN = 200Hz, VIN = 2.5Vp-p, measurement bandwidth = 22kHz OS to OUT VDD - 0.1 2 0 0.25 4 0.2 -79 1 VDD 2 0.1 180 3 1 500 0.2 0.2 10 10 VDD + 0.1 2 fC fCLK/fC (Note 1) 0.001 to 15 100:1 10 VDD - 0.25 25 0.4 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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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7408/MAX7411/MAX7412/MAX7415
ELECTRICAL CHARACTERISTICS--MAX7412/MAX7415 (continued)
(VDD = +3V, filter output measured at OUT pin, 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 Output Current (Internal Oscillator Mode) 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 SHDN = 0 to VDD 0.2 2.5 0.5 10 V V A VDD IDD I SHDN PSRR Operating mode, no load SHDN = GND Measured at DC 2.7 1.13 0.2 70 3.6 1.5 1 V mA A dB fOSC ICLK VIH VIL COSC = 1000pF (Note 3) VCLK = 0 or 3V 2.5 0.5 19 27 12 34 20 kHz A V V SYMBOL CONDITIONS MIN TYP MAX UNITS
ELLIPTIC FILTER (r = 1.6) CHARACTERISTICS--MAX7408/MAX7412
(VDD = +5V for MAX7408, VDD = +3V for MAX7412; 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.) (Note 3) PARAMETER fIN = 0.34fC fIN = 0.63fC fIN = 0.84fC Insertion Gain with DC Gain Error Removed (Note 4) fIN = 0.96fC fIN = fC fIN = 1.60fC fIN = 1.90fC fIN = 4.62fC CONDITIONS MIN -0.4 -0.4 -0.4 -0.4 -0.7 TYP -0.2 0.2 -0.2 0.2 -0.2 -53.4 -53.4 -53.4 MAX 0.4 0.4 0.4 0.4 0.2 -50 -50 -50 dB UNITS
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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters
ELLIPTIC FILTER (r = 1.25) CHARACTERISTICS--MAX7411/MAX7415
(VDD = +5V for MAX7411, VDD = +3V for MAX7415; 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.) (Note 3) PARAMETER fIN = 0.38fC fIN = 0.68fC fIN = 0.87fC Insertion Gain with DC Gain Error Removed (Note 4) fIN = 0.97fC fIN = fC fIN = 1.25fC fIN = 1.43fC fIN = 3.25fC CONDITIONS MIN -0.4 -0.4 -0.4 -0.4 -0.7 TYP -0.2 0.2 -0.2 0.2 -0.2 -38.5 -37.2 -37.2 MAX 0.4 0.4 0.4 0.4 0.2 -34 -35 -35 dB UNITS
MAX7408/MAX7411/MAX7412/MAX7415
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) 27 * 103 / COSC (COSC in pF). Note 4: The input frequencies, fIN, are selected at the peaks and troughs of the ideal elliptic frequency responses.
Typical Operating Characteristics
(VDD = +5V for MAX7408/MAX7411, VDD = +3V for MAX7412/MAX7415; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2; TA = +25C; unless otherwise noted.)
MAX7408/MAX7412 FREQUENCY RESPONSE
MAX7408/11-01
MAX7411/MAX7415 FREQUENCY RESPONSE
fC = 1kHz r = 1.25
MAX7408/11-02
MAX7408/MAX7412 PASSBAND FREQUENCY RESPONSE
MAX7408/11-03
20 0 -20 GAIN (dB) fC = 1kHz r = 1.6
20 0 -20 GAIN (dB)
0.2 0 -0.2 GAIN (dB) -0.4 -0.6 -0.8 -1.0 -1.2 fC = 1kHz r = 1.6 0 204 408 612 816
-40 -60 -80 -100 -120 0 1 2 3 4 5 INPUT FREQUENCY (kHz)
-40 -60 -80 -100 -120 0 1 2 3 4 5 INPUT FREQUENCY (kHz)
1.02k
INPUT FREQUENCY (Hz)
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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7408/MAX7411/MAX7412/MAX7415
Typical Operating Characteristics (continued)
(VDD = +5V for MAX7408/MAX7411, VDD = +3V for MAX7412/MAX7415; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2; TA = +25C; unless otherwise noted.)
MAX7411/MAX7415 PASSBAND FREQUENCY RESPONSE
MAX7408/11-04
MAX7408/MAX7412 PHASE RESPONSE
MAX7408/11-05
MAX7411/MAX7415 PHASE RESPONSE
fC = 1kHz r = 1.25
MAX7408/11-06
0.2 0 -0.2 GAIN (dB) -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 0 204 408 612 816 fC = 1kHz r = 1.25
0 -50 PHASE SHIFT (DEGREES) -100 -150 -200 -250 -300 -350 -400 fC = 1kHz r = 1.6
0 -100 PHASE SHIFT (DEGREES) -200 -300 -400 -500 -600
1.02k
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX7408/11-07
SUPPLY CURRENT vs. TEMPERATURE
MAX7408/11-08
MAX7408 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 -90 A B SEE TABLE A
MAX7408/11-09
1.17 1.16 SUPPLY CURRENT (mA) 1.15 1.14 1.13 1.12 1.11 2.5 3.0 3.5 4.0 4.5 5.0
1.20 1.19 1.18 SUPPLY CURRENT (mA) 1.17 1.16 1.15 1.14 1.13 1.12 1.11 VDD = +3V VDD = +5V
0
5.5
1.10 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
0
1
2
3
4
5
SUPPLY VOLTAGE (V)
AMPLITUDE (Vp-p)
MAX7411 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 A -90 0 1 2 3 AMPLITUDE (Vp-p) A 4 5 B B SEE TABLE A
MAX7408/11-10
0
Table A. THD + Noise Test Conditions
LABEL A B fIN (Hz) 200 1k fC (kHz) 1 5 fCLK (kHz) 100 500 MEASUREMENT BANDWIDTH (kHz) 22 80
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5th-Order, Lowpass, Elliptic, Switched-Capacitor MAX7408/MAX7411/MAX7412/MAX7415
Typical Operating Characteristics (continued)
(VDD = +5V for MAX7408/MAX7411, VDD = +3V for MAX7412/MAX7415; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2; TA = +25C; unless otherwise noted.)
MAX7412 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 -90 0 0.5 1.0 1.5 A 2.0 2.5 3.0 AMPLITUDE (Vp-p) B SEE TABLE A
MAX7408/11-11
MAX7415 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE
-10 -20 THD + NOISE (dB) -30 -40 -50 -60 -70 -80 -90 0 0.5 1.0 1.5 2.0 AMPLITUDE (Vp-p) A A 2.5 3.0 B B SEE TABLE A
MAX7408/11-12
0
0
INTERNAL OSCILLATOR PERIOD vs. SMALL CAPACITANCE (in pF)
MAX7408/11-13
INTERNAL OSCILLATOR PERIOD vs. LARGE CAPACITANCE (in nF)
VDD = +5V 10 OSCILLATOR PERIOD (ms) 8 6 4 2 0 VDD = +3V
MAX7408/11-14
INTERNAL OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
27.3 OSCILLATOR FREQUENCY (kHz) 27.2 27.1 27.0 26.9 26.8 26.7 26.6 COSC = 1000pF 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
MAX7408/11-15
120 100 OSCILLATOR PERIOD (s) 80 60 40 20 0 0 500 VDD = +5V
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27.4
VDD = +3V
1000 1500 2000 2500 3000 3500 CAPACITANCE (pF)
0
50
100
150
200
250
300
350
CAPACITANCE (nF)
SUPPLY VOLTAGE
INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE
MAX7408/11-16
DC OFFSET VOLTAGE vs. TEMPERATURE
MAX7408/11-17
DC OFFSET VOLTAGE vs. SUPPLY VOLTAGE
-0.5 DC OFFSET VOLTAGE (mV) -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0
MAX7408/11-18
28.0 OSCILLATOR FREQUENCY (kHz)
0 -0.5 DC OFFSET VOLTAGE (mV) -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 VDD = +5V VDD = +3V
0
27.5
VDD = +3V
27.0
26.5
VDD = +5V
26.0 COSC = 1000pF 25.5 -50 -30 -10 10 30 50 70 90 110 TEMPERATURE (C)
-40
-20
0
20
40
60
80
100
2.5
3.0
3.5
4.0
4.5
5.0
5.5
TEMPERATURE (C)
SUPPLY VOLTAGE (V)
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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7408/MAX7411/MAX7412/MAX7415
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME COM IN GND VDD OUT OS SHDN CLK FUNCTION Common Input Pin. Biased internally at mid-supply. Bypass externally to GND with 0.1F capacitor. To override internal biasing, drive with an external supply. Filter Input Ground Positive Supply Input, +5V for MAX7408/MAX7411 or +3V for MAX7412/MAX7415 Filter Output 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. Shutdown Input. Drive low to enable shutdown mode; drive high or connect to VDD for normal operation. 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 MAX7408/MAX7411/MAX7412/MAX7415 family of 5th-order, elliptic, lowpass filters provides sharp rolloff with good stopband rejection. All parts operate with a 100:1 clock-to-corner frequency ratio and a 15kHz maximum corner frequency. Most switched-capacitor filters (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 MAX7408/MAX7411/ MAX7412/MAX7415 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,
C2 C4
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 MAX7408/MAX7411/ MAX7412/MAX7415 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 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. 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 MAX7408/MAX7412 have a translation ratio of 1.6 and typically 53dB of stopband rejection. The MAX7411/MAX7415 have a transition ratio of 1.25 (providing a steeper rolloff) and typically 37dB of stopband rejection.
RS + -
L2 C3
L4 C5
VIN C1
RL
Figure 1. 5th-Order Ladder Elliptic Filter Network
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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7408/MAX7411/MAX7412/MAX7415
VSUPPLY RIPPLE 0.1F fC GAIN (dB) VDD TRANSITION RATIO = fS fC fS INPUT IN SHDN OUT COM 0.1F 50k OUTPUT
CLOCK
CLK
MAX7408 MAX7411 MAX7412 MAX7415
GND
OS 0.1F
50k 50k
PASSBAND fC fS
STOPBAND FREQUENCY
Figure 2. Elliptic Filter Response
Figure 3. Offset Adjustment Circuit
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 powered from 0 to VDD. Varying the rate of the external clock adjusts the corner frequency of the filter: f fC = CLK 100 Internal Clock When using the internal oscillator, the capacitance (COSC) on CLK determines the oscillator frequency:
fOSC (kHz) = 27
Estimate the input impedance of the filter by using the following formula: ZIN = 1 (fCLK
CIN )
where fCLK = clock frequency and CIN = 1pF.
Low-Power Shutdown Mode
The MAX7408/MAX7411/MAX7412/MAX7415 have a shutdown mode that is activated by driving SHDN low. In shutdown mode, the filter supply current reduces to 0.2A, and the output of the filter becomes high impedance. For normal operation, drive SHDN high or connect to VDD.
103
Applications Information
Offset (OS) and Common-Mode (COM) Input Adjustment
COM sets the common-mode input voltage and is biased at mid-supply 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 VCOM = VDD 2 (typical)
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 MAX7408/MAX7411/MAX7412/MAX7415'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.
where (VIN - VCOM) is lowpass filtered by the SCF and OS is added at the output stage. See the Electrical
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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7408/MAX7411/MAX7412/MAX7415
V+
VDD INPUT IN
SHDN OUT COM
* OUTPUT
V+ V-
CLOCK
CLK
MAX7408 MAX7411 MAX7412 MAX7415
GND
to the system ground and GND to the negative supply. Figure 4 shows an example of dual-supply operation. Single-supply and dual-supply performance are equivalent. For either single-supply or dual-supply operation, drive CLK and SHDN from GND (V- in dual supply operation) to VDD . Use the MAX7408/MAX7411 for 2.5, and use the MAX7412/MAX7415 for 1.5V. For 5V dual-supply applications, see the MAX291/ MAX292/MAX295/MAX296 and MAX293/MAX294/ MAX297 data sheets.
OS 0.1F 0.1F
Input Signal Amplitude Range
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.
V*CONNECT SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
Anti-Aliasing and Post-DAC Filtering
When using the MAX7408/MAX7411/MAX7412/ MAX7415 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.
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 mid-supply reduces the dynamic range.
Harmonic Distortion
Harmonic distortion arises from nonlinearities within the filter. These nonlinearities generate harmonics when a pure sine wave is applied to the filter input. Table 1 lists typical harmonic distortion values with a 10k load at TA = +25C.
Power Supplies
The MAX7408/MAX7411 operate from a single +5V supply and the MAX7412/MAX7415 operate from a single +3V supply. Bypass V DD to GND with a 0.1F capacitor. If dual supplies are required, connect COM
Table 1. Typical Harmonic Distortion
FILTER fCLK (kHz) 500 MAX7408 100 500 MAX7411 100 500 MAX7412 100 500 MAX7415 100 200 200 1k 2 -90 -87 -90 -90 200 1k 2 -88.2 -87 -85.1 -86 -88.9 -90 -85.7 -90 200 1k 4 -88 -86.6 -86 -93.1 -92 -90 -88 -85.6 fIN (Hz) 1k 4 -88.2 -90 -83.1 -80 -93 -92 -89.5 -88 VIN (Vp-p) TYPICAL HARMONIC DISTORTION (dB) 2nd -85.5 3rd -78.4 4th -92.8 5th -86.9
10
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5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7408/MAX7411/MAX7412/MAX7415
Chip Information
TRANSISTOR COUNT: 1457
________________________________________________________Package Information
8LUMAXD.EPS
______________________________________________________________________________________
11
5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7408/MAX7411/MAX7412/MAX7415
Package Information (continued)
PDIPN.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) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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