MAX7418中文资料

For price, delivery, and to place orders,please contact Maxim Distribution at 1-888-629-4642,or visit Maxim’s website at .General DescriptionThe 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.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.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.ApplicationsADC Anti-Aliasing CT2 Base Stations DAC PostfilteringSpeech ProcessingFeatureso 5th-Order, Lowpass FiltersElliptic Response (MAX7418/MAX7421/ MAX7422/MAX7425)Bessel Response (MAX7419/MAX7423)Butterworth Response (MAX7420/MAX7424)o Clock-Turnable Corner Frequency (1Hz to 45kHz)o Single-Supply Operation+5V (MAX7418–MAX7421)+3V (MAX7422–MAX7425)o Low Power3mA (Operating Mode)0.2µA (Shutdown Mode)o Available in 8-Pin µMAX Package o Low Output Offset: ±4mVMAX7418–MAX74255th-Order, Lowpass,Switched-Capacitor Filters________________________________________________________________Maxim Integrated Products1Typical Operating Circuit19-1821; Rev 0; 11/00Pin ConfigurationOrdering InformationSelector GuideSelector Guide continued at end of data sheet.Ordering Information continued at end of data sheet.M A X 7418–M A X 74255th-Order, Lowpass,Switched-Capacitor Filters 2_______________________________________________________________________________________ABSOLUTE MAXIMUM RATINGSELECTRICAL CHARACTERISTICS —MAX7418–MAX7421(V DD = +5V, filter output measured at OUT, 10k Ω|| 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND,SHDN = V DD , f CLK = 2.2MHz, T A = T MIN to T MAX , unless otherwise noted. Typical values are at T A = +25°C.)Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.V DD to GND..............................................................-0.3V to +6V IN, OUT, COM, OS, CLK, SHDN ................-0.3V to (V DD + 0.3V)OUT Short-Circuit Duration.......................................................1s Continuous Power Dissipation (T A = +70°C)8-Pin µMAX (derate 4.1mW/°C above +70°C).............330mWOperating Temperature RangesMAX74 _ _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°CMAX7418–MAX74255th-Order, Lowpass,_______________________________________________________________________________________3Switched-Capacitor FiltersELECTRICAL CHARACTERISTICS —MAX7418–MAX7421 (continued)(V DD = +5V, filter output measured at OUT, 10k Ω|| 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND,SHDN = V DD , f CLK = 2.2MHz, T A = T MIN to T MAX , unless otherwise noted. Typical values are at T A = +25°C.)ELECTRICAL CHARACTERISTICS —MAX7422–MAX7425(V DD = +3V, filter output measured at OUT pin, 10k Ω|| 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND,SHDN = V DD , f CLK = 2.2MHz, T A = T MIN to T MAX , unless otherwise noted. Typical values are at T A = +25°C.)M A X 7418–M A X 74255th-Order, Lowpass,Switched-Capacitor Filters 4_______________________________________________________________________________________FILTER CHARACTERISTICS(V DD = +5V for MAX7418–MAX7421, V DD = +3V for MAX7422–MAX7425 filter output measured at OUT, 10k Ω||50pF load to GND at OUT, SHDN = V DD , f CLK = 2.2MHz, T A = T MIN to T MAX ,unless otherwise noted.)ELECTRICAL CHARACTERISTICS —MAX7422–MAX7425 (continued)(V DD = +3V, filter output measured at OUT pin, 10k Ω|| 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND,SHDN = V DD , f CLK = 2.2MHz, T A = T MIN to T MAX , unless otherwise noted. Typical values are at T A = +25°C.)MAX7418–MAX74255th-Order, Lowpass,Switched-Capacitor Filters_______________________________________________________________________________________5Note 1:The maximum f C is defined as the clock frequency f CLK = 100 x f C at which the peak S / (THD+N) drops to 68dB with asinusoidal input at 0.2f C . Maximum f C increases as V IN signal amplitude decreases.Note 2:DC insertion gain is defined as ∆V OUT / ∆V IN .Note 3:MAX7418/MAX7421/MAX7422/MAX7425: f OSC (kHz) ≅ 87x103/ C OSC (pF).MAX7419/MAX7420/MAX7423/MAX7424: f OSC (kHz) ≅ 110x103/ C OSC (pF).Note 4:PSRR is the change in output voltage from a V DD of 4.5V and a V DD of 5.5V.FILTER CHARACTERISTICS(V DD = +5V for MAX7418–MAX7421, V DD = +3V for MAX7422–MAX7425 filter output measured at OUT, 10k Ω||50pF load to GND at OUT, SHDN = V DD , f CLK = 2.2MHz, T A = T MIN to T MAX ,unless otherwise noted.)__________________________________________Typical Operating Characteristics(V DD = +5V for MAX7418–MAX7421, V DD = +3V for MAX7422–MAX7425, f CLK = 2.2MHz, SHDN = V DD , V COM = V OS = V DD / 2, T A = +25°C, unless otherwise noted.)-90-60-70-80-50-40-30-20-1001040206080100MAX7418/MAX7422FREQUENCY RESPONSE (ELLIPTIC, r = 1.6)M A X 7418 t o c 01INPUT FREQUENCY (kHz)G A I N (d B )-60-40-50-20-300-1010040206080100MAX7419/MAX7423FREQUENCY RESPONSE (BESSEL)INPUT FREQUENCY (kHz)G A I N (d B )-80-60-70-30-40-500-10-2010040206080100MAX7420/MAX7424FREQUENCY RESPONSE (BUTTERWORTH)INPUT FREQUENCY (kHz)G A I N (d B )____________________________Typical Operating Characteristics (continued)(V DD = +5V for MAX7418–MAX7421, V DD = +3V for MAX7422–MAX7425, f CLK = 2.2MHz, SHDN = V DD , V COM = V OS = V DD / 2, T A = +25°C, unless otherwise noted.M A X 7418–M A X 74255th-Order, Lowpass,Switched-Capacitor Filters 6_______________________________________________________________________________________-90-60-70-80-50-40-30-20-10010040206080100MAX7421/MAX7425FREQUENCY RESPONSE (ELLIPTIC, r = 1.25)INPUT FREQUENCY (kHz)G A I N (d B)-4.0-3.0-3.5-1.5-2.0-2.50-0.5-1.00.59.04.513.518.022.5MAX7420/MAX7424PASSBAND FREQUENCY RESPONSEINPUT FREQUENCY (kHz)G A I N (d B)-1.0-0.6-0.8-0.2-0.40.200.409.04.513.518.022.5MAX7418/MAX7422PASSBAND FREQUENCY RESPONSE(ELLIPTIC, r = 1.6)INPUT FREQUENCY (kHz)G A I N (d B)-4.0-3.0-3.5-1.5-2.0-2.50-0.5-1.00.509.04.513.518.022.5MAX7419/MAX7423PASSBAND FREQUENCY RESPONSE(BESSEL)INPUT FREQUENCY (kHz)G A I N (d B )-1.0-0.6-0.8-0.2-0.40.200.409.04.513.518.022.5MAX7421/MAX7425PASSBAND FREQUENCY RESPONSE(ELLIPTIC, r = 1.25)INPUT FREQUENCY (kHz)G A I N (d B )-450-350-400-200-250-300-50-100-15000812416202428MAX7418/MAX7422PHASE RESPONSE (ELLIPTIC, r = 1.6)INPUT FREQUENCY (kHz)P H A S E S H I F T (D E G R E E S )M A X 7418 t o c 09-250-200-100-150-5000841216202428MAX7419/MAX7423PHASE RESPONSE (BESSEL)M A X 7418 t o c 10INPUT FREQUENCY (kHz)P H A S E S H I F T (D E G R E E S )-350-250-300-150-200-50-10000812416202428MAX7420/MAX7424PHASE RESPONSE (BUTTERWORTH)M A X 7418 t o c 11INPUT FREQUENCY (kHz)P H A S E S H I F T (D E G R E E S )-450-350-400-200-250-300-50-100-1500812416202428MAX7424/MAX7425PHASE RESPONSE (ELLIPTIC, r = 1.25)M A X 7418 t o c 12INPUT FREQUENCY (kHz)P H A S E S H I F T (D E G R E E S )____________________________Typical Operating Characteristics (continued)(V DD = +5V for MAX7418–MAX7421, V DD = +3V for MAX7422–MAX7425, f CLK = 2.2MHz, SHDN = V DD , V COM = V OS = V DD / 2, T A = +25°C, unless otherwise noted.MAX7418–MAX74255th-Order, Lowpass,Switched-Capacitor Filters_______________________________________________________________________________________7-90-70-80-40-50-60-10-20-300021345MAX7418THD + NOISE vs. INPUT SIGNAL AMPLITUDE(ELLIPTIC, r = 1.6)AMPLITUDE (Vp-p)T H D + N (d B )-90-70-80-40-50-60-10-20-300021345MAX7421THD + NOISE vs. INPUT SIGNAL AMPLITUDE(ELLIPTIC, r = 1.25)AMPLITUDE (Vp-p)T H D + N (d B )-90-70-80-40-50-60-10-20-300021345MAX7419THD + NOISE vs. INPUT SIGNAL AMPLITUDE(BESSEL)AMPLITUDE (Vp-p)T H D + N (d B )-90-70-80-40-50-60-10-20-30021345MAX7420THD + NOISE vs. INPUT SIGNAL AMPLITUDE(BUTTERWORTH)AMPLITUDE (Vp-p)T H D + N (d B )-90-70-80-40-50-60-10-20-30001.00.51.52.0 2.53.0MAX7422THD + NOISE vs. INPUT SIGNAL AMPLITUDE(ELLIPTIC, r = 1.6)AMPLITUDE (Vp-p)T H D + N (d B)-90-70-80-40-50-60-10-20-3001.00.51.52.02.53.0MAX7423THD + NOISE vs. INPUT SIGNAL AMPLITUDE(BESSEL)AMPLITUDE (Vp-p)T H D + N (d B)-90-70-80-40-50-60-30-20-10000.51.01.52.02.53.0MAX7424THD + NOISE vs. INPUT SIGNAL AMPLITUDE(BUTTERWORTH)AMPLITUDE (Vp-p)T H D + N (d B )-90-70-80-40-50-60-30-20-10000.51.01.52.02.53.0MAX7425THD + NOISE vs. INPUT SIGNAL AMPLITUDE(ELLIPTIC, r = 1.25)AMPLITUDE (Vp-p)T H D + N (d B )02000100040003000600050007000INTERNAL OSCILLATOR FREQUENCY vs. SMALL CAPACITANCE (pF)CAPACITANCE ( pF)O S C I L L A T O R F R E Q U E N C Y (k H z )110100100010000____________________________Typical Operating Characteristics (continued)(V DD = +5V for MAX7418–MAX7421, V DD = +3V for MAX7422–MAX7425, f CLK = 2.2MHz, SHDN = V DD , V COM = V OS = V DD / 2, T A = +25°C, unless otherwise noted.M A X 7418–M A X 74255th-Order, Lowpass,Switched-Capacitor Filters 8_______________________________________________________________________________________0214356101001000INTERNAL OSCILLATOR FREQUENCY vs. LARGE CAPACITANCE (nF)CAPACITANCE (nF)O S C I L L A T O R F R E Q U E N C Y (H z )2.32.52.92.73.13.32.53.53.04.04.55.05.5ELLIPTIC SUPPLY CURRENT vs. SUPPLY VOLTAGEM A X 7418 t o c 25SUPPLY VOLTAGE (V)S U P P L Y C U R R E N T (µA )84.085.084.586.085.586.587.02.53.54.03.04.55.05.5ELLIPTIC INTERNAL OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGESUPPLY VOLTAGE (V)O S C I L L A T O R F R E Q U E N C Y (k H z )84.085.084.586.085.586.587.0-4010-15356085ELLIPTIC INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURETEMPERATURE (°C)O S C I L L A T O R F R E Q U E N C Y (k H z) 2.52.62.82.72.93.0-4010-15356085ELLIPTIC SUPPLY CURRENTvs. TEMPERATURETEMPERATURE (°C)S U P P L Y C U R R E N T (m A )MAX7418–MAX74255th-Order, Lowpass,Switched-Capacitor Filters_______________________________________________________________________________________9Pin Description_______________Detailed DescriptionThe 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 toproduce higher order filters. The advantage to this approach is ease of design. H owever, 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.Typical Operating Characteristics (continued)(V DD = +5V for MAX7418–MAX7421, V DD = +3V for MAX7422–MAX7425, f CLK = 2.2MHz, SHDN = V DD , V COM = V OS = V DD / 2, T A = +25°C, unless otherwise noted.0.51.51.02.02.52.53.53.04.04.55.05.5DC OFFSET VOLTAGE vs. SUPPLY VOLTAGEM A X 7418 t o c 28SUPPLY VOLTAGE (V)D C O F F SE T V O L T A G E (m V )01.00.52.01.52.53.0-4010-15356085DC OFFSET VOLTAGE vs. TEMPERATURETEMPERATURE (°C)D C O F F SE T V O L T A G E (m V )Filter OutputOUT 5Offset 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.OS 6Shutdown Input. Drive low to enable shutdown mode; drive high or connect to V DD for normal operation. SHDN 7Clock Input. Connect an external capacitor (C OSC ) from CLK to ground. To override the internal oscillator,connect CLK to an external clock: f C = f CLK /100.CLK8Positive Supply Input: +5V for MAX7418–MAX7421, +3V for MAX7422–MAX7425. Bypass V DD to GND with a 0.1µF capacitor.V DD 4GroundGND 3PIN Filter Input IN 2Common 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 1FUNCTIONNAMEM A X 7418–M A X 74255th-Order, Lowpass,Switched-Capacitor Filters 10______________________________________________________________________________________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.Elliptic CharacteristicsLowpass 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 ).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.The stopband begins at the stopband frequency, f S . At frequencies above f S , the filter’s gain does not exceed the gain at f S . The corner frequency, f C , is defined as 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:r = f S / f CThe MAX7418/MAX7422 have a transition ratio of 1.6and 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.Bessel CharacteristicsLowpass Bessel filters such as the MAX7419/MAX7423delay 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.Butterworth CharacteristicsLowpass 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.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 SignalExternal ClockThese 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 DD . Varying the rate of the external clock adjusts the corner frequency of the filter:Figure 1. 5th-Order Ladder Filter NetworkFigure 2. Elliptic Filter ResponseMAX7418–MAX74255th-Order, Lowpass, Switched-Capacitor Filters______________________________________________________________________________________11Internal ClockWhen using the internal oscillator, the capacitance (C OSC ) on CLK determines the oscillator frequency:wherek = 87 x 103 for theMAX7418/MAX7421/MAX7422/MAX7425 andk = 110 x 103for theMAX7419/MAX7420/MAX7423/ MAX7424.Since C OSC is in the low picofarads, minimize the stray 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 a100:1 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 FrequenciesThe 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.Estimate the input impedance of the filter by using the following formula:where f CLK = clock frequency and C IN = 1pF.Low-Power Shutdown ModeThe MAX7418–MAX7425have a shutdown mode that isactivated 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-tion, drive SHDN high or connect to V DD .Applications InformationOffset (OS) and Common-Mode (COM)Input AdjustmentCOM 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 bywhere (V IN - V COM ) is lowpass filtered by the SCF and OS is added at the output stage. See the Electrical Characteristics table for the input voltage range of COMf OSC (kHz) kC OSC (pF)=Figure 4. Offset Adjustment CircuitA: 1kHz INPUT SIGNALB: MAX7419 BESSEL FILTER RESPONSE; f C = 5kHzC: MAX7420 BUTTERWORTH FILTER RESPONSE; f C = 5kHz200µs/divFigure 3. Bessel vs. Butterworth Filter ResponseM A X 7418–M A X 74255th-Order, Lowpass,Switched-Capacitor Filtersand OS. Changing the voltage on COM or OS signifi-cantly from midsupply reduces the dynamic range.Power SuppliesThe MAX7418–MAX7421 operate from a single +5V supply and the MAX7422–MAX7425 operate from a sin-gle +3V supply. Bypass V DD to GND with a 0.1µF capacitor. If dual supplies are required, connect COM to the system ground and GND to the negative supply.Figure 5 shows an example of dual-supply operation.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 operation) to V DD . Use the MAX7418–MAX7421 for ±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.Input Signal Amplitude RangeThe 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 Typic al Operating Charac teristic s show the THD + Noise response as the input signal’s peak-to-peak amplitude is varied.Anti-Aliasing and Post-DAC FilteringWhen 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.Harmonic DistortionHarmonic 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 10k Ωload at T A = +25°C.Table 1. MAX7418/MAX7421/MAX7422/MAX7425 Typical Harmonic DistortionFigure 5. Dual-Supply OperationMAX7418–MAX74255th-Order, Lowpass,Switched-Capacitor Filters______________________________________________________________________________________13Chip InformationTRANSISTOR COUNT:1457PROCESS: BiCMOSOrdering Information (continued)Selector Guide (continued)M A X 7418–M A X 74255th-Order, Lowpass,Switched-Capacitor Filters Maxim c annot assume responsibility for use of any c irc uitry other than c irc uitry entirely embodied in a Maxim produc t. No c irc uit patent lic enses 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 ProductsPrinted USAis a registered trademark of Maxim Integrated Products.________________________________________________________Package Information。