DCO's, Anti-Aliasing, and Filters

[inman at interpath.com]

I just read in Nuts and Volts about MAXIM's new filters:  5TH-ORDER 
FILTER ("5th-order lowpass, switched-capacitor Butterworth and Bessel 
filters available in 8-pin mMAX and DIP packages," MAXIM web page) and an 
8TH-ORDER ELLIPTIC, LOWPASS SWITCHED-CAPACITOR FILTERS ("...provide corner
frequencies from 1Hz to 10kHz and draw supply currents of only 2mA, making
them well suited for low-power anti-aliasing and post-DAC filtering 
applications," MAXIM web page).  Be a bit careful before you begin to design 
with some of the 8TH-ORDER stuff in the spec sheets; only the 7400 is ready. 
The others are future products (a fine print truth pointed out in the 
promotional stuff).  The cool thing about the 8TH order filters is that
they will run off of a capacitor OR a clock (input clock / 100).  If you
are designing a microchip that is already sending out a square wave, why
not send a second one out to the MAXIM filter?  For that matter, why not 
vary the speed of the microchip output to vary the cutoff frequency of
the filter and create a sweeping filter?  Or, if you don't want to program
a PIC, etc..., why not use a 555 to control the cutoff, instead of a control 
voltage?  You could even use the control voltage input on the 555 to 
vary the speed of the 555 and use that to vary the filter cutoff.

The best part:  8TH ORDER FILTER $2.00 US.

Although ads can be very misleading sometimes, it sure does sound as if
this little chip would reduce a tremendous amount of undesired alias
waveforms caused by imprecise timing of the period of square waves or
A/D coversion of phase accumulator waveforms.  At a decent price.

Any thoughts from DSP folks with the brains to do the math?

Spec sheets and some promotional material may be found at their web site.

http://www.maxim-ic.com/NewProd.htm


Elliot  "Probably Re-inventing the Wheel, but Having Fun Imagining
	No One Has Ever Seen a Rock Roll"