8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MA
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8th-Order, Lowpass, Bessel, Switched-Capacitor Filters
MAX7401/MAX7405 8th-order, lowpass, Bessel, switched-capacitor filters (SCFs) operate from single (MAX7401) (MAX7405) supply. These devices draw only supply current allow corner frequencies from 5kHz, making them ideal low-power post-DAC filtering anti-aliasing applications. They feature shutdown mode that reduces supply current 0.2µA. clocking options available these devices: self-clocking (through external capacitor) external clocking tighter corner-frequency control. offset adjust allows adjustment output level. MAX7401/MAX7405 Bessel filters provide overshoot fast settling. Their fixed response simplifies design task selecting clock frequency. 8th-Order, Lowpass Bessel Filters Noise Distortion: -82dB Noise Clock-Tunable Corner Frequency (1Hz 5kHz) 100:1 Clock-to-Corner Ratio Single-Supply Operation (MAX7401) (MAX7405) Power (Operating Mode) 0.2µA (Shutdown Mode) Available 8-Pin SO/DIP Packages Output Offset: ±5mV
Features
MAX7401/MAX7405
Applications
Anti-Aliasing Post-DAC Filtering Air-Bag Electronics Base Stations Speech Processing
PART MAX7401CSA MAX7401CPA MAX7401ESA MAX7401EPA MAX7405CSA MAX7405CPA MAX7405ESA MAX7405EPA
Ordering Information
TEMP. RANGE +70°C +70°C -40°C +85°C -40°C +85°C +70°C +70°C -40°C +85°C -40°C +85°C PIN-PACKAGE Plastic Plastic Plastic Plastic
Configuration
VIEW
SHDN
VSUPPLY 0.1µF INPUT SHDN OUTPUT
Typical Operating Circuit
MAX7401 MAX7405
SO/DIP
MAX7401 MAX7405
CLOCK 0.1µF
Maxim Integrated Products
free samples latest literature: http://www.maxim-ic.com, phone 1-800-998-8800. small orders, phone 1-800-835-8769.
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
ABSOLUTE MAXIMUM RATINGS
MAX7401 .-0.3V MAX7405 .-0.3V OUT, COM, .-0.3V (VDD 0.3V) SHDN.-0.3V Short-Circuit Duration.1sec Continuous Power Dissipation +70°C) 8-Pin (derate 5.88mW/°C above +70°C).471mW 8-Pin (derate 9.09mW/°C above +70°C) .727mW Operating Temperature Ranges MAX740 _C_A .0°C +70°C MAX740 _E_A .-40°C +85°C Storage Temperature Range .-65°C +150°C Lead Temperature (soldering, 10sec) .+300°C
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS-MAX7401
+5V, filter output measured OUT, 50pF load OUT, COM, 0.1µF from GND, SHDN VDD, fCLK 100kHz, TMIN TMAX, unless otherwise noted. Typical values +25°C.) PARAMETER FILTER CHARACTERISTICS Corner Frequency Clock-to-Corner Ratio Clock-to-Corner Tempco Output Voltage Range Output Offset Voltage Insertion Gain with Output Offset Removed Total Harmonic Distortion plus Noise Voltage Gain Input Voltage Range THD+N Input, externally driven Voltage Range VCOM Output, internally biased Input Resistance Clock Feedthrough Resistive Output Load Drive Maximum Capacitive Load Input Leakage Current Input Leakage Current CLOCK Internal Oscillator Frequency Clock Input Current Clock Input High Clock Input fOSC ICLK COSC 1000pF (Note VCLK SHDN GND, VCOM (VDD (Note RCOM VOFFSET VCOM VCOM (Note 200Hz, 4Vp-p, measurement bandwidth 22kHz -0.1 0.25 0.15 VCOM ±0.1 ±0.1 ±0.1 mVp-p fCLK (Note 0.001 100:1 0.25 ppm/°C SYMBOL CONDITIONS UNITS
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters
ELECTRICAL CHARACTERISTICS-MAX7401 (continued)
+5V, filter output measured OUT, 50pF load OUT, COM, 0.1µF from GND, SHDN VDD, fCLK 100kHz, TMIN TMAX, unless otherwise noted. Typical values +25°C.) PARAMETER POWER REQUIREMENTS Supply Voltage Supply Current Shutdown Current Power-Supply Rejection Ratio SHUTDOWN SHDN Input High SHDN Input SHDN Input Leakage Current VSDH VSDL SHDN ±0.1 SHDN PSRR Operating mode, load, SHDN GND, driven from Measured SYMBOL CONDITIONS UNITS
MAX7401/MAX7405
ELECTRICAL CHARACTERISTICS-MAX7405
+3V, filter output measured OUT, 50pF load OUT, COM, 0.1µF from GND, SHDN VDD, fCLK 100kHz, TMIN TMAX, unless otherwise noted. Typical values +25°C.) PARAMETER FILTER CHARACTERISTICS Corner Frequency Clock-to-Corner Ratio Clock-to-Corner Tempco Output Voltage Range Output Offset Voltage Insertion Gain with Output Offset Removed Total Harmonic Distortion plus Noise Voltage Gain Input Voltage Range Voltage Range Input Resistance Clock Feedthrough Resistance Output Load Drive Maximum Capacitive Load Input Leakage Current Input Leakage Current SHDN GND, VCOM (VDD (Note THD+N VCOM RCOM internally biased externally driven VOFFSET VCOM VCOM (Note 200Hz, 2.5Vp-p, measurement bandwidth 22kHz -0.1 0.25 0.03 VCOM ±0.1 ±0.1 ±0.1 fCLK/fC (Note 0.001 100:1 0.25 ppm/°C mVp-p SYMBOL CONDITIONS UNITS
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
ELECTRICAL CHARACTERISTICS-MAX7405 (continued)
+3V, filter output measured OUT, 50pF load OUT, COM, 0.1µF from GND, SHDN VDD, fCLK 100kHz, TMIN TMAX, unless otherwise noted. Typical values +25°C.) PARAMETER CLOCK Internal Oscillator Frequency Clock Input Current Clock Input High Clock Input POWER REQUIREMENTS Supply Voltage Supply Current Shutdown Current Power-Supply Rejection Ratio SHUTDOWN SHDN Input High SHDN Input SHDN Input Leakage Current VSDH VSDL SHDN ±0.1 SHDN PSRR Operating mode, load, SHDN GND, driven from Measured fOSC ICLK COSC 1000pF (Note VCLK SYMBOL CONDITIONS UNITS
FILTER CHARACTERISTICS-MAX7401/MAX7405
(VDD MAX7401, MAX7405; filter output measured OUT; 50pF load OUT; SHDN VDD; VCOM fCLK 100kHz; TMIN TMAX; unless otherwise noted. Typical values +25°C.) PARAMETER 0.5fC Insertion Gain Relative Gain CONDITIONS -1.0 -3.3 -0.8 -3.0 -0.6 -2.7 UNITS
Note maximum defined clock frequency, fCLK which peak SINAD drops 68dB with sinusoidal input 0.2fC. Note insertion gain defined VOUT VIN. Note voltages above saturate input result 75µA typical input leakage current. Note MAX7401, fOSC (kHz) COSC (pF). MAX7405, fOSC (kHz) COSC (pF).
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters
Typical Operating Characteristics
(VDD MAX7401, MAX7405; fCLK 100kHz; SHDN VDD; VCOM +25°C; unless otherwise noted.)
FREQUENCY RESPONSE
MAX7401 toc01
MAX7401/MAX7405
PASSBAND FREQUENCY RESPONSE
MAX7409 toc02
PHASE RESPONSE
1kHz PHASE SHIFT (DEGREES) -100 -150 -200 -250 -300 -350 -400
MAX7401 toc03
1kHz GAIN (dB)
1kHz -0.5 GAIN (dB) -1.0 -1.5 -2.0 -2.5 -3.0
INPUT FREQUENCY (kHz)
-3.5 1010 INPUT FREQUENCY (Hz)
1200
1600
2000
INPUT FREQUENCY (Hz)
SUPPLY CURRENT SUPPLY VOLTAGE
MAX7401 toc04
SUPPLY CURRENT TEMPERATURE
MAX7401 toc05
OFFSET VOLTAGE SUPPLY VOLTAGE
VCOM OFFSET VOLTAGE (mV) MAX7405 MAX7401
MAX7401 toc06
SUPPLY CURRENT (mA) MAX7405 MAX7401 LOAD
2.03 LOAD 2.02 SUPPLY CURRENT (mA) 2.01 MAX7401 2.00 1.99 MAX7405 1.98 1.97
SUPPLY VOLTAGE
TEMPERATURE (°C)
SUPPLY VOLTAGE
OFFSET VOLTAGE TEMPERATURE
MAX7401 toc07
INTERNAL OSCILLATOR FREQUENCY COSC CAPACITANCE
MAX7401 toc08
NORMALIZED OSCILLATOR FREQUENCY SUPPLY VOLTAGE
NORMALIZED OSCILLATOR FREQUENCY 1.15 1.10 1.05 1.00 0.95 0.90 0.85 0.80 MAX7401 MAX7405 COSC 390pF
MAX7401 toc09
VCOM OFFSET VOLTAGE (mV)
10,000 OSCILLATOR FREQUENCY (kHz)
1.20
1000
-0.5
-1.0
-1.5 TEMPERATURE (°C)
0.01 1000 COSC CAPACITANCE (nF)
SUPPLY VOLTAGE
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
Typical Operating Characteristics (continued)
(VDD MAX7401, MAX7405; fCLK 100kHz; SHDN VDD; VCOM +25°C; unless otherwise noted.)
NORMALIZED OSCILLATOR FREQUENCY TEMPERATURE
MAX7401 toc10
MAX7401 PLUS NOISE INPUT SIGNAL AMPLITUDE
MAX7401 toc11
MAX7401 PLUS NOISE INPUT SIGNAL AMPLITUDE RESISTIVE LOAD
NOISE (dB) 200Hz 1kHz MEASUREMENT 22kHz
MAX7401 toc12
1.04 NORMALIZED OSCILLATOR FREQUENCY 1.03 1.02 1.01 1.00 0.99 0.98 0.97 0.96 MAX7405 MAX7401 COSC 390pF
NOISE (dB) LOAD (SEE TABLE
TEMPERATURE (°C)
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
MAX7405 PLUS NOISE INPUT SIGNAL AMPLITUDE
MAX7401 toc13
MAX7405 PLUS NOISE INPUT SIGNAL AMPLITUDE RESISTIVE LOAD
NOISE (dB) 200Hz 1kHz MEASUREMENT 22kHz
MAX7401 toc14
NOISE (dB) LOAD (SEE TABLE
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
Table Plus Noise Input Signal Amplitude Test Conditions
TRACE (Hz) 1000 (kHz) fCLK (kHz) MEASUREMENT BANDWIDTH (kHz)
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
Description
NAME SHDN FUNCTION Common Input. Biased internally mid-supply. Bypass externally with 0.1µF capacitor. override internal biasing, drive with external supply. Filter Input Ground Positive Supply Input: MAX7401, MAX7405 Filter Output Offset Adjust Input. adjust output offset, bias externally. Connect offset adjustment needed. Refer Offset Common-Mode Input Adjustment section. Shutdown Input. Drive enable shutdown mode; drive high connect normal operation. Clock Input. override internal oscillator, connect external clock; otherwise, connect external capacitor (COSC) from internal oscillator frequency.
_Detailed Description
MAX7401/MAX7405 Bessel filters provide overshoot fast settling responses. Both parts operate with 100:1 clock-to-corner frequency ratio 5kHz maximum corner frequency. Lowpass Bessel filters such MAX7401/MAX7405 delay frequency components equally, preserving shape step inputs (subject attenuation higher frequencies). Bessel filters settle quickly-an important characteristic applications that multiplexer (mux) select input signal analog-todigital converter (ADC). anti-aliasing filter placed between must settle quickly after channel selected. Figure shows difference between Bessel Butterworth filters when 1kHz square wave applied filter input. With filter cutoff frequencies 5kHz, trace shows Bessel filter response trace shows Butterworth filter response.
2V/div
2V/div
2V/div
200µs/div 1kHz INPUT SIGNAL BESSEL FILTER RESPONSE; 5kHz BUTTERWORTH FILTER RESPONSE; 5kHz
Figure Bessel Butterworth Filter Response
Background Information
Most switched-capacitor filters (SCFs) designed with biquadratic sections. Each section implements filtering poles, sections cascaded produce higher order filters. advantage this approach ease design. However, this type design highly sensitive component variations section's high. alternative approach emulate passive network using switched-capacitor integrators with summing scaling. Figure shows basic 8th-order ladder filter structure.
Figure 8th-Order Ladder Filter Network
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
switched-capacitor filter such MAX7401/ MAX7405 emulates passive ladder filter. filter's component sensitivity when compared cascaded biquad design because each component affects entire filter shape, just pole-zero pair. other words, mismatched component biquad design will have concentrated error respective poles, while same mismatch ladder filter design results error distributed over poles.
Low-Power Shutdown Mode
These devices feature shutdown mode that activated driving SHDN low. shutdown mode, filter's supply current reduces 0.2µA (typ) output becomes high impedance. normal operation, drive SHDN high connect VDD.
_Applications Information
Offset Common-Mode Input Adjustment
voltage sets common-mode input voltage biased mid-supply with internal resistordivider. Bypass with 0.1µF capacitor connect COM. applications requiring offset adjustment level shifting, apply external bias voltage through resistor-divider network shown Figure (Note: leave unconnected.) output voltage represented this equation: VOUT (VIN VCOM) with VCOM (typical), where (VIN VCOM) lowpass filtered SCF, added output stage. Electrical Characteristics voltage range Changing voltage significantly from mid-supply reduces filter's dynamic range.
Clock Signal
External Clock MAX7401/MAX7405 family SCFs designed with external clocks that have duty cycle. When using external clock with these devices, drive with CMOS gate powered from VDD. Varying rate external clock adjusts corner frequency filter follows:
fCLK
Internal Clock When using internal oscillator, connect capacitor OSC) between ground. value capacitor determines oscillator frequency follows:
fOSC (kHz) COSC COSC
where MAX7401 MAX7405. Minimize stray capacitance that does affect internal oscillator frequency. Vary rate internal oscillator adjust filter's corner frequency 100:1 clock-to-corner frequency ratio. example, internal oscillator frequency 100kHz produces nominal corner frequency 1kHz.
Power Supplies
MAX7401 operates from single supply, MAX7405 operates from single supply. Bypass with 0.1µF capacitor. dual supplies required (±2.5V MAX7401, ±1.5V MAX7405), connect system ground connect
VSUPPLY
Input Impedance Clock Frequencies
MAX7401/MAX7405's input impedance effectively that switched-capacitor resistor inversely proportional frequency. input impedance values determined below represent average input impedance since input current continuous. rule, driver with output impedance less than filter's input impedance. Estimate input impedance filter using following formula:
0.1µF INPUT SHDN 0.1µF
OUTPUT
MAX7401 MAX7405
CLOCK 0.1µF
(fCLK
where fCLK clock frequency 3.37pF.
Figure Offset Adjustment Circuit
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
Table Typical Harmonic Distortion
FILTER fCLK (kHz) MAX7401 MAX7405 1000 1000 (kHz) (Hz) (Vp-p) TYPICAL HARMONIC DISTORTION (dB)
Anti-Aliasing Post-DAC Filtering
INPUT
SHDN
OUTPUT
CLOCK
MAX7401 MAX7405
0.1µF 0.1µF
When using MAX7401/MAX7405 anti-aliasing post-DAC filtering, synchronize filter clocks. clocks synchronized, beat frequencies alias into passband. high clock-to-corner frequency ratio (100:1) also eases requirements pre- post-SCF filtering. input, lowpass filter prevents aliasing frequencies around clock frequency into passband. output, lowpass filter attenuates clock feedthrough. high clock-to-corner frequency ratio allows simple lowpass filter, with cutoff frequency above corner frequency, provide input anti-aliasing reasonable output clock attenuation.
V*DRIVE SHDN LOW-POWER SHUTDOWN MODE.
Harmonic Distortion
Harmonic distortion arises from nonlinearities within filter. These nonlinearities generate harmonics when pure sine wave applied filter input. Table lists MAX7401/MAX7405's typical harmonic-distortion values with load +25°C.
Figure Dual-Supply Operation
negative supply. Figure shows example dual-supply operation. Single- dual-supply performance equivalent. either single- dual-supply operation, drive SHDN from dualsupply operation) VDD. dual-supply applications, MAX291-MAX297.
Chip Information
TRANSISTOR COUNT: 1116
Input Signal Amplitude Range
optimal input signal range determined observing voltage level which total harmonic distortion plus noise (THD+N) minimized given corner frequency. Typical Operating Characteristics show graphs devices' THD+N response input signal's peak-to-peak amplitude varied. These measurements made with biased midsupply.
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
_Package Information
SOICN.EPS
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
Package Information (continued)
PDIPN.EPS
8th-Order, Lowpass, Bessel, Switched-Capacitor Filters MAX7401/MAX7405
NOTES
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
_Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 1999 Maxim Integrated Products Printed registered trademark Maxim Integrated Products.
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