MAX260BCNG+ ,Microprocessor Programmable Universal Active FiltersApplicationsMAX260AMRG -55°C to +125°C CERDIP 1%µP-Tuned FiltersMAX260BMRG -55°C to +125°C CERDIP 2 ..
MAX260BCWG ,Microprocessor Programmable Universal Active FiltersApplications
pP Tuned Filters
Anti-Aliasing Filters
Digital Signal Processing
Adaptive Filter ..
MAX260BCWG+ ,Microprocessor Programmable Universal Active FiltersFeaturesThe MAX260/MAX261/MAX262 CMOS dual second-♦ Filter Design Software Availableorder universal ..
MAX260BENG ,Microprocessor Programmable Universal Active FiltersApplications
pP Tuned Filters
Anti-Aliasing Filters
Digital Signal Processing
Adaptive Filter ..
MAX260BENG+ ,Microprocessor Programmable Universal Active FiltersELECTRICAL CHARACTERISTICS+ -(V = +5V, V = -5V, CLK = CLK = ±5V 350kHz for the MAX260 and 1.5MHz fo ..
MAX260BEWG+ ,Microprocessor Programmable Universal Active FiltersMAX260/MAX261/MAX26219-0352; Rev 2; 7/02Microprocessor ProgrammableUniversal Active Filters
MAX5940DESA+T ,IEEE 802.3af PD Interface Controller for Power-Over-EthernetELECTRICAL CHARACTERISTICS(V = (GND - V ) = 48V, GATE = PGOOD = PGOOD = OUT = OPEN, UVLO = V , T = ..
MAX5941ACSE ,IEEE 802.3af-Compliant Power-Over-Ethernet Interface/PWM Controller for Power DevicesFeaturesThe MAX5941A/MAX5941B integrate a complete power Powered Device InterfaceIC for powered de ..
MAX5941BCSE ,IEEE 802.3af-Compliant Power-Over-Ethernet Interface/PWM Controller for Power DevicesApplicationsMAX5941BCSE 0°C to +70°C 16 SO 50IP PhonesWireless Access NodesPin ConfigurationInterne ..
MAX5941BESE ,IEEE 802.3af-Compliant Power-Over-Ethernet Interface/PWM Controller for Power DevicesELECTRICAL CHARACTERISTICS (continued)(V = (GND - V ) = 48V, GATE = PGOOD = PGOOD = OPEN, V- tied t ..
MAX5941BESE+T ,IEEE 802.3af-Compliant Power-Over-Ethernet Interface/PWM Controller for Power DevicesFeaturesThe MAX5941A/MAX5941B integrate a complete power♦ Powered Device InterfaceIC for powered de ..
MAX5942AESE ,IEEE 802.3af power-over-ethernet interface/PWM controller for power deviceFeaturesThe MAX5942A/MAX5942B integrate a complete power Powered Device InterfaceIC for powered d ..
MAX260BCNG+-MAX260BCWG+-MAX260BENG+-MAX260BEWG+-MAX261ACWG+-MAX261BCNG+-MAX261BCWG+-MAX261BENG+-MAX262BCNG+-MAX262BENG+-MAX262BEWG+
Microprocessor Programmable Universal Active Filters
General DescriptionThe MAX260/MAX261/MAX262 CMOS dual second-
order universal switched-capacitor active filters allow
microprocessor control of precise filter functions. No
external components are required for a variety of band-
pass, lowpass, highpass, notch, and allpass configura-
tions. Each device contains two second-order filter
sections that place center frequency, Q, and filter oper-
ating mode under programmed control.
An input clock, along with a 6-bit f0program input,
determine the filter's center or corner frequency without
affecting other filter parameters. The filter Q is also pro-
grammed independently. Separate clock inputs for
each filter section operate with either a crystal, RC net-
work, or external clock generator.
The MAX260 has offset and DC specifications superior
to the MAX261 and MAX262 and a center frequency
(f0) range of 7.5kHz. The MAX261 handles center fre-
quencies to 57kHz, while the MAX262 extends the cen-
ter frequency range to 140kHz by employing lower
clock-to-f0ratios. All devices are available in 24-pin DIP
and small outline packages in commercial, extended,
and military temperature ranges.
ApplicationsµP-Tuned Filters
Anti-Aliasing Filters
Digital Signal Processing
Adaptive Filters
Signal Analysis
Phase-Locked Loops
FeaturesFilter Design Software AvailableMicroprocessor Interface64-Step Center Frequency Control128-Step Q ControlIndependent Q and f0ProgrammingGuaranteed Clock to f0Ratio-1% (A grade)75kHz f0Range (MAX262)Single +5V and ±5V Operation
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active FiltersLPA
INB
LPB
BPBN.C.
HPA
N.C.
BPA
TOP VIEW
OSC OUT
GNDCLK OUT
INA
HPBCLKB
CLKA
MAX260
LPA
INB
LPB
BPBOP IN
HPA
OP OUT
BPA
HPB
OSC OUT
CLK OUT
INA
GNDCLKB
CLKA
MAX261
MAX262
Pin Configurations
Ordering InformationOUTPUTHPLPINBPHPLPIN
INPUT
+5VV+
GND
-5VV-
CLKA OSC CLKOUTCLKB
PROGRAM
INPUTS
CRYSTAL
FOURTH-ORDER BANDPASS FILTER
MAX260
MAX261
MAX262
FILTER
FILTER
Functional Diagram19-0352; Rev 2; 7/02
PARTTEMP RANGEPACKAGEA C C U R A C Y
MAX260ACNG0°C to +70°CPlastic DIP1%
MAX260BCNG0°C to +70°CPlastic DIP2%
MAX260AENG-40°C to +85°CPlastic DIP1%
MAX260BENG-40°C to +85°CPlastic DIP2%
MAX260ACWG0°C to +70°CWide SO1%
MAX260BCWG0°C to +70°CWide SO2%
MAX260AMRG-55°C to +125°CCERDIP1%
MAX260BMRG-55°C to +125°CCERDIP2%
*All devices—24-pin packages 0.3in-wide packages
Ordering Information continued at end of data sheet.
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
ABSOLUTE MAXIMUM RATINGSStresses 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.
Total Supply Voltage (V+to V-) .............................................15V
Input Voltage, any pin ..........................(V-- 0.3V) to (V++ 0.3V)
Input Current, any pin ......................................................±50mA
Power Dissipation
Plastic DIP (derate 8.33mW/°C above 70°C) ...............660mW
CERDIP (derate 12.5mW/°C above 70°C) .................1000mW
Wide SO (derate 11.8mW/°C above 70°C) ..................944mW
Operating Temperature Ranges
MAX260/MAX261/MAX262XCXG .......................0°C to +70°C
MAX260/MAX261/MAX262XEXG .....................-40°C to +85°C
MAX260/MAX261/MAX262XMXG ..................-55°C to +125°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (Soldering, 10s) ................................+300°C
ELECTRICAL CHARACTERISTICS+= +5V, V-= -5V, CLKA= CLKB= ±5V 350kHz for the MAX260 and 1.5MHz for the MAX261/MAX262, fCLK/f0= 199.49 for
MAX260/MAX261 and 139.80 for MAX262, Filter Mode 1, TA= +25°C, unless otherwise noted.)
PARAMETERCONDITIONSMINTYPMAXUNITSf0 Center Frequency RangeSee Table 1
Maximum Clock FrequencySee Table 1
MAX260A±0.2±1.0
MAX260B±0.2±2.0
MAX261/MAX262A±0.2±1.0fCLK/f0 Ratio Error (Note 1)TA = TMIN to TMAX
MAX261/MAX262B±0.2±2.0
f0 Temperature Coefficient-5ppm/°C
Q = 8MAX260A±1±6
Q = 8MAX260B±1±10
Q = 32MAX260A±2±10
Q = 32MAX260B±2±15
Q = 64MAX260A±4±20
Q = 64MAX260B±4±25
Q = 8MAX261/MAX262A±1±6
Q = 8MAX261/MAX262B±1±10
Q = 32MAX261/MAX262A±2±10
Q = 32MAX261/MAX262B±2±15
Q = 64MAX261/MAX262A±4±20
Q Accuracy (deviation from ideal
continuous filter) (Note 2)
TA = TMIN to
TMAX
Q = 64MAX261/MAX262B±4±25
Q Temperature Coefficient±20ppm/°C
MAX260±0.1±0.3DC Lowpass Gain AccuracyMAX261/MAX262±0.1±0.5dB
MAX260-5
MAX261/MAX262-5Gain Temperature CoefficientLowpass (at D.C.)
Bandpass (at f0)
MAX260/MAX261/MAX262+20
ppm/°C
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
ELECTRICAL CHARACTERISTICS (continued)(V+= +5V, V-= -5V, CLKA= CLKB= ±5V 350kHz for the MAX260 and 1.5MHz for the MAX261/MAX262, fCLK/f0= 199.49 for
MAX260/MAX261 and 139.80 for MAX262, Filter Mode 1, TA= +25°C, unless otherwise noted.)
PARAMETERCONDITIONSMINTYPMAXUNITSMAX260A±0.05±0.25
MAX260B±0.15±0.45
MAX261A±0.40±1.00
MAX261B±0.80±1.60
MAX262A±0.40±1.20
TA = TMIN to TMAX, Q = 4
Mode 1
MAX262B±0.80±1.60
MAX260A±0.075±0.30
MAX260B±0.075±0.50
MAX261A±0.50±1.10
MAX261B±0.90±1.60
MAX262A±0.50±1.30
Offset Voltage At Filter
Outputs—LP, BP, HP (Note 3)
Mode 3
MAX262B±0.90±1.60
Offset Voltage Temperature
Coefficient
fCLK/f0 = 100.53, Q = 4
TA = TMIN to TMAX±0.75mV/°C
Clock Feedthrough±4mV
Crosstalk-70dB
Q = 1, 2nd-Order, LP/BPSee Typ. Oper. Char.
4th-Order LP (Figure 26)90Wideband Noise
4th-Order BP (Figure 24) (Note 4)100
µVRMS
Harmonic Distortion at f0Q = 4, VIN = 1.5VP-P-67dB
Supply Voltage RangeTA = TMIN to TMAX±2.37±5±6.3V
MAX2601520
MAX2611620Power Supply Current (Note 5)TA = TMIN to TMAX
CMOS Level Logic Inputs
MAX2621620
Shutdown Supply CurrentQ0A - Q6A = all 0,
CMOS Level Logic Inputs (Note 5)1.5mA
INTERNAL AMPLIFIERSOutput Signal SwingTA = TMIN to TMAX, 10kΩ load (Note 6)±4.75V
Source50Output Signal Circuit CurrentSink2mA
Power Supply Rejection Ratio0Hz to 10kHz-70dB
Gain Bandwidth Product2.5MHz
Slew Rate6V/µs
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
ELECTRICAL CHARACTERISTICS (for V±= ±2.5V ±5%)(V+= +2.37V, V-= -2.37V, CLKA= CLKB= ±2.5V 250kHz for the MAX260 and 1MHz for the MAX261/MAX262, fCLK/f0= 199.49 for
MAX260/MAX261 and 139.80 for MAX262, Filter Mode 1, TA= +25°C, unless otherwise noted.)
PARAMETERCONDITIONSMINTYPMAXUNITSf0 Center Frequency Range(Note 7)
Maximum Clock Frequency(Note 7)
MAX26XA±0.11fCLK/f0 Ratio Error
(Notes 1, 8)Q = 8MAX26XB±0.12%
MAX260A±2±6Q = 8
fCLK/f0 = 199.49MAX260B±2±10
MAX261A±2±6fCLK/f0 = 199.49MAX261B±2±10
MAX262A±2±6
Q Accuracy (deviation from ideal
continuous filter)
(Notes 2, 8)
fCLK/f0 = 139.80MAX262B±2±10
Output Signal SwingAll Outputs (Note 6)±2V
Power Supply CurrentCMOS Level Logic Inputs (Note 5)7mA
Shutdown CurrentCMOS Level Logic Inputs (Note 5)0.35mA
Note 1:fCLK/f0accuracy is tested at 199.49 on the MAX260/MAX261, and at 139.8 on the MAX262.
Note 2:Q accuracy tested at Q = 8, 32, and 64. Q of 32 and 64 tested at 1/2 stated clock frequency.
Note 3:The offset voltage is specified for the entire filter. Offset is virtually independent of Q and fCLK/f0ratio setting. The test clock
frequency for mode 3 is 175kHz for the MAX260 and 750kHz for the MAX261/MAX262.
Note 4:Output noise is measured with an RC output smoothing filter at 4 ✕ f0to remove clock feedthrough.
Note 5:TTL logic levels are: HIGH = 2.4V, LOW = 0.8V. CMOS logic levels are: HIGH = 5V, LOW = 0V. Power supply current is typi-
cally 4mA higher with TTL logic and clock input levels.
Note 6:On the MAX260 only, the HP output signal swing is typically 0.75V less than the LP or BP outputs.
Note 7:At ±2.5V supplies, the f0range and maximum clock frequency are typically 75% of values listed in Table 1.
Note 8:fCLK/f0and Q accuracy are a function of the accuracy of internal capacitor ratios. No increase in error is expected at ±2.5V
as compared to ±5V; however, these parameters are only tested to the extent indicated by the MIN or MAX limits.
INTERFACE SPECIFICATIONS (Note 9)+= +5V, V+= -5V, TA= +25°C, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSWR Pulse WidthtWR250150ns
Address SetuptAS25ns
Address HoldtAH0ns
Data SetuptDS10050ns
Data HoldtDH100ns
Logic Input HighVIHWR, D0, D1, A0–A3, CLKA, CLKB
TA =TMIN to TMAX2.4V
Logic Input LowVILWR, D0, D1, A0–A3, CLKA, CLKB
TA =TMIN to TMAX0.8VInput Leakage CurrentIIN
WR, D0, D1, A0–A3, CLKB
CLKA
TA =TMIN to TMAX
6µA
Input CapacitanceCINWR, D0, D1, A0–A3, CLKA, CLKB15pF
Note 9:Interface timing specifications are guaranteed by design and are not subject to test.
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
Pin Description
PIN
MAX260MAX261/
MAX262
NAMEFUNCTIONV+Positive supply voltage16V-Negative supply voltage17GND
Analog Ground. Connect
to the system ground for
dual supply operation or
mid-supply for single sup-
ply operation. GND should
be well bypassed in single
supply applications.11CLKA
Input to the oscillator and
clock input to section A.
This clock is internally
divided by 2.12CLKB
Clock input to filter B. This
clock is internally divided
by 2.8CLK OUTC l ock outp ut for cr ystal
and R- C osci l l ator op er ati on18OSC OUTConnects to crystal or R-C
for self-clocked operation
PIN
MAX260MAX261/
MAX262
NAMEFUNCTION5, 235, 23INA, INBFilter inputs
1, 211, 21BPA, BPBBandpass outputs
24, 2224, 22LPA, LPBLowpass outputs
3, 143, 20HPA, HPBHighpass/notch/allpass
outputs15WRWrite enable input
15, 13,
10, 7
14, 13,
10, 7
A0, A1,
A2, A3
Address inputs for f0 and
Q input data locations
20, 619, 6D0, D1Data inputs for f0 and Q
programmingOP OUT
Outp ut of uncom m i tted
op am p on M AX 261/AX 262 onl y. P i n 2 i s a no-
connect on the M AX 260.OP IN
Inver ti ng i np ut of uncom - i tted op am p on M AX 261/AX 262 onl y ( noni nver ti ng np ut i s i nter nal l y connected
to g r ound ) . P i n 4 i s a no-
connect on the M AX 260.
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
Q ERROR vs. CLOCK FREQUENCY
MAX260
MAX260/61/62 toc01
CLOCK FREQUENCY (MHz)
Q ERROR (%)
MODE 4±5V
25°C
Q = 8
fCLK/f0 → N = 0
MODES 2 & 3
MODE 1
IDD vs. POWER SUPPLY VOLTAGEMAX260/61/62 toc02
V+ TO V- (V)
IDD
(mA)967101112
CLK FREQ = 500KHz
25°C
CONTROL PINS (5V, 0V)
CLOCKS (5V, 0V)
CLOCKS (5V, -5V)
IDD vs. CLOCK FREQUENCY
MAX260/61/62 toc03
CLOCK FREQUENCY (MHz)
(mA)
CLOCK (2.4V, 0.8V)
CLOCK (5V, 0V)
±5V
CONTROL PINS (5V, 0V)
25°C
CLOCK (5V, -5V)
Q ERROR vs. CLOCK FREQUENCY
MAX261/MAX262
MAX260/61/62 toc04
CLOCK FREQUENCY (MHz)
Q ERROR (%)
MODE 3
MODE 2
MODES 1, 4
±5V
Q = 8
TA = 25°C
→ N = 0fCLK
FCLK/F0 ERROR vs. CLOCK FREQUENCY
MAX261/MAX262
MAX260/61/62 toc05
CLOCK FREQUENCY (MHz)
CLK
ERROR (%)
MODES 2, 3
MODES 1, 4±5V
Q = 8
TA = 25°CfCLK→ N = 0
OUTPUT SIGNAL SWING
vs. CLOCK FREQUENCY
MAX260/61/62 toc06
CLOCK FREQUENCY (MHz)
PEAK TO PEAK, OUTPUT SWING (V)
MAX261/MAX262 ALL MODES
MAX260 MODE 4
±5V
25°C
Q = 8
fCLK/f0→ N = 0
MAX260 MODES 1, 2, 3
Q = 1Q = 8Q = 64MODELPBPHP/AP/NLPBPHP/AP/NLPBPHP/AP/N-84-90-84-80-82-85-72-73-85-88-90-88-84-82-84-77-73-76-84-90-88-80-82-82-73-73-74
MAX261/
MAX262-83-89-84-79-81-85-71-73-85-87-89-86-81-81-86-73-73-86-89-88-85-83-80-82-75-72-74-87-88-85-80-82-80-71-72-72
MAX2604-87-88-86-81-81-86-71-72-86
MEASUREMENT
BANDWIDTHQ = 1Q = 8Q = 64Wideband-84-80-72
3kHz-87-87-86
C Message
Weighted-93-93-93
Wideband RMS Noise(db ref. to 2.47VRMS, 7VP-P)
±5V Supplies
Note 1:fCLK= 1MHz for MAX261/MAX262, fCLK= 350kHz for MAX260
Note 2:fCLK/f0ratio programmed at N = 63 (see Table 2)
Note 3:Clock feedthrough is removed with an RC lowpass ar 4f0, ie., R = 3.9kΩ,
C = 2000pF for MAX261.
Noise Spectral Distribution(MAX261, fCLK= 1MHz, dB ref. to 2.47VRMS,
7VP-P)
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
IntroductionEach MAX260/MAX261/MAX262 contains two second-
order switched-capacitor active filters. Figure 1 shows
the filter's state variable topology, employed with two
cascaded integrators and one summing amplifier. The
MAX261 and MAX262 also contain an uncommitted
amplifier. On-chip switches and capacitors provide
feedback to-control each filter section's f0and Q.
Internal capacitor ratios are primarily responsible for
the accuracy of these parameters. Although these
switched-capacitor networks (SCN) are in fact sampled
systems, their behavior very closely matches that of
continuous filters, such as RC active filters. The ratio of
the clock frequency to the filter center frequency
(fCLK/f0) is kept large so that ideal second-order state-
variable response is maintained.
The MAX262 uses a lower range of sampling (fCLK/f0)
ratios than the MAX260 or MAX261 to allow higher
operating f0frequencies and signal bandwidths. These
reduced sample rates result in somewhat more devia-
tion from ideal continuous filter parameters than with
the MAX260/MAX261. However, these differences can
be compensated using Figure 20 (see Application
Hints) or Maxim's filter design software.
The MAX260 employs auto-zero circuitry not included
in the MAX261 or MAX262. This provides improved DC
characteristics, and improved low-frequency perform-
ance at the expense of high-end f0and signal band-
width. The N/HP/AP outputs of the MAX260 are internal-
ly sample-and-held as a result of its auto-zero
operation. Signal swing at this output is somewhat
reduced as a result (MAX260 only). See Table 1 for
bandwidth comparisons of the three filters.
Maxim also provides design programs that aid in con-
verting filter response specifications into the f0and Q
program codes used by the MAX260 series devices.
This software also precompensates f0and Q when low
sample rates are used.
It is important to note that, in all MAX260 series filters,
the filter's internal sample rate is one half the input
clock rate (CLKAor CLKB) due to an internal division
by two. All clock-related data, tables, and other dis-
cussions in this data sheet refer to the frequency at the
CLKAor CLKBinput, i.e., twice the internal sample rate,
unless specifically stated otherwise.
Quick Look Design ProcedureThe MAX260, MAX261, and MAX262, with Maxim's filter
design software, greatly simplify the design procedures
for many active filters. Most designs can be realized
using a three-step process described in this section. If
the design software is not used, or if the filter complexi-
ty is beyond the scope of this section, refer to the
remainder of this data sheet for more detailed applica-
tions and design information.M0
SCNINS1
MODE
SELECT
SCN
Q0–Q6
(TABLE 3)
F0–F5
(TABLE 2)
SAMPLE-HOLD
MAX260 ONLY
N/HP/AP
SCN = SWITCH-CAPACITOR NETWORK∫∫
SCN
SCN
S-H
Figure 1. Filter Block Diagram (One Second-Order Section)
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
Step 1—Filter DesignStart with the program “PZ” to determine what type of
filter is needed. This helps determine the type
(Butterworth, Chebyshev, etc.) and the number of poles
for the optimum choice. The program also plots the fre-
quency response and calculates the pole/zero (f0) and
Q values for each second-order section. Each
MAX260/MAX261/MAX262 contains two second-order
sections, and devices can be cascaded for higher
order filters.
MAX260
MAX261*
MAX262*
INA
OUT5
(20)14
LPA
HPA
BPA
LPB
HPB
BPB
INB
CLKA
CLKB
16(15)
20(19)
DB-25 MALE PLUG
(BACK VIEW)
15(14)18(17)17(16)CLK IN
TTL
(SEE FIGURE 4)
0.1μF0.1μF
-5V+5VV-GND
*PIN NUMBERS IN ( ) ARE FOR MAX261/MAX262
100 AB$ = "FILTER A" : GOSUB 150 : REM GET DATA FOR SECTION A
110 ADD = 0 : GOSUB 220 : REM WRITE DATA TO THE PRINTER PORT
120 AB$ = "FILTER B" : GOSUB 150 : REM GET DATA FOR B
130ADD = 32 : GOSUB 220 : REM WRITE DATA TO PRINTER PORT
140GOTO 100
150PRINT "MODE (1 to 4, see Table 5) "; AB$; : INPUT M
160IF M<1 OR M>4 THEN GOTO 150
170PRINT "CLOCK RATIO (0 to 63, N of Table 2) "; AB$; : INPUT F
180IF F<0 OR F>63 THEN GOTO 170
190PRINT "Q (0 to 127, N of Table 3) "; AB$; : INPUT Q
200IF Q<0 OR Q>127 THEN GOTO 190 ELSE : PRINT
210 RETURN
220 LPRINT CHR$(ADD+M-1); : ADD = ADD+4
230FOR I = 1 TO 3
240X = (ADD + (F - 4*INT(F/4))) : LPRINT CHR$(X);
250F=INT(F/4) : ADD = ADD + 4
260NEXT I
270FOR I = 1 TO 4
280X=(ADD + (Q - 4*INT(Q/4))) : LPRINT CHR$(X);
290 Q=I (Q/4) :: ADD = ADD + 4
300NEXT I
310 RETURN
Figure 2. Basic Program and Hardware Connections to Parallel Printer Port for “Quick Look” Using a PC
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
Step 2—Generate Programming
CoefficientsStarting with the f0and Q values obtained in Step 1, use
the program “MPP” to generate the digital coefficients
that program each second-order section's f0and Q. The
program displays values for “N” (“N = _ for f0” and “N =
_ for Q”). N is the decimal equivalent of the binary code
that sets the filter section’s f0or Q. These are the same
“N”s that are listed in Tables 2 and 3.
An input clock frequency and filter mode must also be
selected in this step; however, if a specific-clock rate is
not selected, “GEN” picks one. With regard to mode
selection, mode 1 is the most convenient choice for
most bandpass and lowpass filters. Exceptions are
elliptic bandpass and lowpass filters, which require
mode 3. Highpass filters also use mode 3, while allpass
filters use mode 4. For further information regarding
these filter modes, see the Filter Operating Modessec-
tion.
Step 3—Loading the FilterWhen the N values for the f0and Q of each second-
order filter section are determined, the filter can then be
programmed and operated. What follows is a con-
venient method of programming the filter and evalu-
ating a design if a PC is available.
A short BASIC program loads data into the MAX260/
MAX261/MAX262 through the PC's parallel printer port.
The program asks for the filter mode, as well as the N
values for the f0and Q of each section. These coeffi-
cients are then loaded into the filter in the form of ASCII
characters. This program can be used with or without
Maxim's other filter design software. The program and
the appropriate hardware connections for a Centronics-
type printer port are shown in Figure 2.
Filter Design SoftwareMaxim provides software programs to help speed the
transition from frequency response design require-
ments to working hardware. A series of programs are
available, including:
Program PZ.Given the requirements, such as center
frequency, Q, passband ripple, and stopband attenua-
tion, PZ calculates the pole frequencies, Q's, zeros,
and the number of stages needed.
Program MPP.For programmed filters, MPP computes
the input codes to use and describes the expected
performance of the design.
Program FR.When a design of one or more stages is
completed, FR checks the final cascaded assembly.
The output frequency response can be compared with
that expected from PZ.
Program PR.BASAllows a MAX260/MAX261/MAX262
to be programmed through a personal computer. The
mode, f0, and Q of each section are typed in, and the
proper codes are sent to the filter through the comput-
er’s parallel printer port. This program is also provided
in Figure 2.
Other design programs are also included for use with
other Maxim filter products.
Other Filter ProductsMaxim has developed a number of other filter products
in addition to the MAX260, MAX261, and MAX262.
PIN-PROGRAMMABLE ACTIVE FILTERS—A dual sec-ond-order universal filter that needs no external compo-
nents. A microprocessor interface is not required.
MAX2630.4Hz to 30kHz f0range
MAX2641Hz to 75kHz f0range
RESISTOR AND PIN-PROGRAMMABLE FILTERS—Adual second-order universal filter where f0adjustment
beyond pin-programmable resolution employs external
resistors.
MAX2650.4Hz to 30kHz f0range. Includes two
uncommitted op amps.
MAX2661Hz to 75kHz f0range. Includes two un-
committed op amps.
MF10Industry Standard, Resistor Programmed Only
PIN-PROGRAMMABLE BANDPASS FILTERS—Adual second-order bandpass that needs no external
components. A microprocessor interface is not
required.
MAX2670.4Hz to 30kHz f0range
MAX2681Hz to 75kHz f0range
PROGRAMMABLE ANTI-ALIAS FILTER—A program-mable dual second-order continuous (not switched)
lowpass filter. No clock noise is generated. Designed
for use as an anti-alias filter in front of, or as a smooth-
ing filter following, any sampled filter or system.
MAX2701kHz to 25kHz Cutoff Frequency Range
5th-ORDER LOW PASS FILTER—Features zero offsetand drift errors for designs requiring high DC accuracy.
MAX280, LT10620.1Hz to 20kHz Cutoff Frequency
Range
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
PARTQMODEfCLKf011Hz–400kHz0.01Hz–4.0kHz21Hz–425kHz0.01Hz–6.0kHz31Hz–500kHz0.01Hz–5.0kHz41Hz–400kHz0.01Hz–4.0kHz11Hz–500kHz0.01Hz–5.0kHz21Hz–700kHz0.01Hz–10.0kH31Hz–700kHz0.01Hz–5.0kHz41Hz–600kHz0.01Hz–4.0kHz11Hz–750kHz0.01Hz–7.5kHz21Hz–500kHz0.01Hz–7.0kHz31Hz–400kHz0.01Hz–4.0kHz
MAX26041Hz–750kHz0.01Hz–7.5kHz140Hz–4.0MHz0.4Hz–40kHz240Hz–4.0MHz0.5Hz–57kHz340Hz–4.0MHz0.4Hz–40kHz440Hz–4.0MHz0.4Hz–40kHz140Hz–2.7MHz0.4Hz–27kHz240Hz–2.1MHz0.5Hz–30kHz
MAX261
PARTQMODEfCLKf0340Hz–1.7MHz0.4Hz–17kHz440Hz–2.7MHz0.4Hz–27kHz140Hz–2.0MHz0.4Hz–20kHz240Hz–1.2MHz0.4Hz–18kHz340Hz–1.2MHz0.4Hz–12kHz
MAX261440Hz–2.0MHz0.4Hz–20kHz140Hz–4.0MHz1.0Hz–100kHz240Hz–4.0MHz1.4Hz–140kHz340Hz–4.0MHz1.0Hz–100kHz440Hz–4.0MHz1.0Hz–100kHz140Hz–2.5MHz1.0Hz–60kHz240Hz–1.4MHz1.4Hz–50kHz340Hz–1.4MHz1.0Hz–35kHz440Hz–2.5MHz1.0Hz–60kHz140Hz–1.5MHz1.0Hz–37kHz240Hz–0.9MHz1.4Hz–32kHz340Hz–0.9MHz1.0Hz–22kHz
MAX262440Hz–1.5MHz1.0Hz–37kHz
Table 1. Typical Clock and Center Frequency LimitsINALPAN/HP/APABPA674
A0–A3WRCLKACLKBOSC OUTCLK OUTOP OUTOP IND0, D1
MODE
A PROGRAM MEMORY
MODE, f0, Q
INTERFACE
LOGIC
QCK
INBLPBN/HP/APBBPB67
MODE
B PROGRAM MEMORY
MODE, f0, Q÷2
QCK
GND
MAX261/MAX262 ONLY∫∫
Figure 3. MAX260/MAX261/MAX262 Block Diagram
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
fCLK/f0 RATIO
MAX260/MAX261MAX262PROGRAM CODE
MODES 1,3,4MODE 2MODES 1,3,4MODE 2NF5F4F3F2F1F0Table 2. fCLK/f0Program Selection Table
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
Detailed Descriptionand Q ProgrammingFigure 3 shows a block diagram of the MAX260. Each
second-order filter section has its own clock input and
independent f0and Q control. The actual center fre-
quency is a function of the filter's clock rate, 6-bit f0
control word (see Table 2), and operating mode. The Q
of each section is also set by a separate programmed
input (see Table 3). This way, each half of a MAX260/
MAX261/MAX262 is tuned independently so that com-
plex filter polynomials can be realized. Equations that
convert program code numbers to fCLK/f0and Q values
are listed in the notes beneath Tables 2 and 3.
Oscillator and Clock InputsThe clock circuitry of the MAX260/MAX261/MAX262
can operate with a crystal, resistor-capacitor (RC) net-
work, or an external clock generator as shown in Figure
4. If an RC oscillator is used, the clock rate, fCLK, nomi-
nally equals 0.45/RC.
The duty cycle of the clock at CLKAand CLKBis unim-
portant because the input is internally divided by 2 to
generate the sampling clock for each filter section. It is
important to note that this internal division also halves
the sample rate when considering aliasing and other
sampled system phenomenon.
Microprocessor Interface f0, Q, and mode-selection data are stored in internal
program memory. The memory contents are updated
by writing to addresses selected by A0–A3. D0, and D1
are the data inputs. A map of the memory locations is
shown in Table 4. Data is stored in the selected
address on the rising edge of WR. Address and data
inputs are TTL and CMOS compatible when the filter is
powered from ±5V. With other power supply voltages,
CMOS logic levels should be used. Interface timing is
shown in Figure 5. Note:Clock inputs CLKAand CLKB
have no relation to the digital interface. They control the
switched-capacitor filter sample rate only.
Some noise may be generated on the filter outputs by
transitions at the logic inputs. If this is objectionable,
fCLK/f0 RATIO
MAX260/MAX261MAX262PROGRAM CODE
MODES 1,3,4MODE 2MODES 1,3,4MODE 2NF5F4F3F2F1F0Table 2. fCLK/f0Program Selection Table (continued)
Note 1:For the MAX260/MAX261, fCLK/f0= (64 + N)π / 2 in modes 1, 3, and 4, where N varies from 0 to 63.
Note 2:For the MAX262, fCLK/f0= (26 s N)π / 2 in modes 1, 3, and 4, where N varies 0 to 63.
Note 3:In mode 2, all fCLK/f0ratios are divided by √2. The functions are then:
MAX260/MAX261 fCLK/f0= 1.11072 (64 + N), MAX262 fCLK/f0= 1.11072 (26 + N)
MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
PROGRAMMED QPROGRAM CODE
MODES
1,3,4
MODENQ6Q5Q4Q3Q2Q1Q00.500*0.707*0*0000000
PROGRAMMED QPROGRAM CODE
MODES
1,3,4
MODENQ6Q5Q4Q3Q2Q1Q0
Table 3. Q Program Selection Table
Note 4:* Writing all 0s into Q0A–Q6A on Filter A activates a low-power shutdown mode. BOTH filter sections are deactivated.
Therefore, this Q value is only achievable in filter B.
