
                       SUBPROGRAM BP

Bandpass filters can be designed using the following techniques:

    (i) cascading second order sections with each section having a different
    center frequency.

    (ii) cascading second order IDENTICAL sections and using resistive
    feedback in the multiple feedback technique.

With technique (i), a MAX260 cannot always implement a bandpass using a single
clock input. The different center frequencies may require separate clocks for
each filter section. ( The  design procedure for MAX260 is supported by
Program MPP ). With technique (ii) a high order bandpass needs only one
clock along with a few external resistors. This program, BP, assumes that
technique (ii) is used.
***

With the MAX267 and MAX268 bandpass filters the clock ratio and Q are set
by strapping programming pins to high or low logic levels. The clock/
center frequency ratio can be set as follows:

              100-200 for MAX267
              41-140 for MAX268


When a multiple feedback topology is used ( BP assumes this topology ),
then all second order stages have the same Q and the same clock/center
frequency ratio. The 7-bit code for Q and the 5-bit code for the clock/
center frequency ratio are derived by the program.

BP also derives a set of resistor values. The absolute values are not unique
and others will work as well provided the same ratios are maintained. Due
consideration must be given to output loading effects for resistor values
less than 10Kohm.
***

                          PROGRAM OUTPUT

The resistor specs are written out on files

                   BP1.R for first design
                   BP2.R for second design, etc.

Frequency response files are also written to disk and it is possible to
have several frequency response files for each design:

    Design BP1.R has frequency response files BP1A, BP1B etc.
    Design BP2.R has frequency response files BP2A, BP2B etc.
    and so on for subsequent designs

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                          GRAPHICS

During subprogram BP the user has the option of examining the frequency
response using the FV graphics option. If the output files are to be used for
graphics then it is advisable to use sufficient sample points to make a smooth
curve. The minimum should be 50 and the graphics can handle at the most 200.
If the output files are to be used as printed files then any number of points
may be used. If the user expects to plot with a log frequency axis then best
results will be obtained using the log option for the plotting intervals.
The graphics option may be used later so long as the output files remain in the
directory.
***
