Microprocessor Programmable
Universal Active Filters
Program PRꢁBAS Allows a MAX260/MAX261/MAX262
Step 2—Generate Programming
Coefficients
to be programmed tꢂrougꢂ a personal computerꢀ Tꢂe
mode, f , and Q of eacꢂ section are typed in, and tꢂe
0
Starting witꢂ tꢂe f and Q values obtained in Step 1, use
0
proper codes are sent to tꢂe filter tꢂrougꢂ tꢂe comput-
er’s parallel printer portꢀ Tꢂis program is also provided
in Figure 2ꢀ
tꢂe program “MPP” to generate tꢂe digital coefficients
tꢂat program eacꢂ second-order section's f and Qꢀ Tꢂe
0
program displays values for “N” (“N = _ for f ” and “N =
0
_ for Q”)ꢀ N is tꢂe decimal equivalent of tꢂe binary code
Otꢂer design programs are also included for use witꢂ
otꢂer Maxim filter productsꢀ
tꢂat sets tꢂe filter section’s f or Qꢀ Tꢂese are tꢂe same
0
“N”s tꢂat are listed in Tables 2 and 3ꢀ
Other Filter Products
Maxim ꢂas developed a number of otꢂer filter products
in addition to tꢂe MAX260, MAX261, and MAX262ꢀ
An input clock frequency and filter mode must also be
selected in tꢂis stepꢄ ꢂowever, if a specific-clock rate is
not selected, “GEN” picks oneꢀ Witꢂ regard to mode
selection, mode 1 is tꢂe most convenient cꢂoice for
most bandpass and lowpass filtersꢀ Exceptions are
elliptic bandpass and lowpass filters, wꢂicꢂ require
mode 3ꢀ ꢁigꢂpass filters also use mode 3, wꢂile allpass
filters use mode 4ꢀ For furtꢂer information regarding
tꢂese filter modes, see tꢂe Filter Operating Modes sec-
tionꢀ
PIN-PRꢀGRAMMABLE ACTIVE FILTERS—A dual sec-
ond-order universal filter tꢂat needs no external compo-
nentsꢀ A microprocessor interface is not requiredꢀ
MAX263 0ꢀ4ꢁH to 30kꢁH f range
0
MAX264 1ꢁH to ꢃ5kꢁH f range
0
RESISTꢀR AND PIN-PRꢀGRAMMABLE FILTERS—A
dual second-order universal filter wꢂere f adjustment
0
beyond pin-programmable resolution employs external
resistorsꢀ
Step 3—Loading the Filter
Wꢂen tꢂe N values for tꢂe f and Q of eacꢂ second-
0
order filter section are determined, tꢂe filter can tꢂen be
programmed and operatedꢀ Wꢂat follows is a con-
venient metꢂod of programming tꢂe filter and evalu-
ating a design if a PC is availableꢀ
MAX265 0ꢀ4ꢁH to 30kꢁH f rangeꢀ Includes two
0
uncommitted op ampsꢀ
MAX266 1ꢁH to ꢃ5kꢁH f rangeꢀ Includes two un-
0
A sꢂort BASIC program loads data into tꢂe MAX260/
MAX261/MAX262 tꢂrougꢂ tꢂe PC's parallel printer portꢀ
Tꢂe program asks for tꢂe filter mode, as well as tꢂe N
committed op ampsꢀ
MF10
Industry Standard, Resistor Programmed Only
values for tꢂe f and Q of eacꢂ sectionꢀ Tꢂese coeffi-
0
PIN-PRꢀGRAMMABLE BANDPASS FILTERS—A
dual second-order bandpass tꢂat needs no external
componentsꢀ A microprocessor interface is not
requiredꢀ
cients are tꢂen loaded into tꢂe filter in tꢂe form of ASCII
cꢂaractersꢀ Tꢂis program can be used witꢂ or witꢂout
Maxim's otꢂer filter design softwareꢀ Tꢂe program and
tꢂe appropriate ꢂardware connections for a Centronics-
type printer port are sꢂown in Figure 2ꢀ
MAX267 0ꢀ4ꢁH to 30kꢁH f range
0
MAX268 1ꢁH to ꢃ5kꢁH f range
0
Filter Design Software
PRꢀGRAMMABLE ANTI-ALIAS FILTER—A program-
mable dual second-order continuous (not switcꢂed)
lowpass filterꢀ No clock noise is generatedꢀ Designed
for use as an anti-alias filter in front of, or as a smootꢂ-
ing filter following, any sampled filter or systemꢀ
Maxim provides software programs to ꢂelp speed tꢂe
transition from frequency response design require-
ments to working ꢂardwareꢀ A series of programs are
available, including:
Program PZꢁ Given tꢂe requirements, sucꢂ as center
frequency, Q, passband ripple, and stopband attenua-
tion, PZ calculates tꢂe pole frequencies, Q's, Heros,
and tꢂe number of stages neededꢀ
MAX270 1kꢁH to 25kꢁH Cutoff Frequency Range
5th-ꢀRDER LꢀW PASS FILTER—Features Hero offset
and drift errors for designs requiring ꢂigꢂ DC accuracyꢀ
Program MPPꢁ For programmed filters, MPP computes
tꢂe input codes to use and describes tꢂe expected
performance of tꢂe designꢀ
MAX280, LT1062 0ꢀ1ꢁH to 20kꢁH Cutoff Frequency
Range
Program FRꢁ Wꢂen a design of one or more stages is
completed, FR cꢂecks tꢂe final cascaded assemblyꢀ
Tꢂe output frequency response can be compared witꢂ
tꢂat expected from PZꢀ
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