Author Topic: Digital adjustable brick wall low pass filter  (Read 1006 times)

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Offline OgreVorbisTopic starter

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Digital adjustable brick wall low pass filter
« on: August 22, 2019, 11:46:51 pm »
Hi,

I am in need of an adjustable brick wall filter. I'd actually prefer a studio style rack mount unit, but it looks like this is going to have to be something I build myself because I can't find anything.

I plan to use this chip: https://www.digikey.com/product-detail/en/maxim-integrated/MAX294CPA/MAX294CPA-ND/1512387

And to generate a clock signal for it using Si5351A to adjust the corner frequency.

Is this a good way to go about doing this? Will there be noise from the clock signal? Is it stable enough?

Maybe there is already a directly programmable filter out there, so I eliminate the need for the clock?
 

Offline ledtester

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Re: Digital adjustable brick wall low pass filter
« Reply #1 on: August 23, 2019, 02:53:06 am »
I would just try it. The chip is advertised as "easy to use", and "no external resistors or capacitors required" so there shouldn't be a lot of complications.

Be sure to read page 7 of the datasheet especially the section "Uncommitted Op-Amp" - it can help with clock noise filtering among other things.

A google book search for "max293 circuit" got some hits in "Analog Circuits Cookbook" by Ian Hickman, so checking that out might help.


 

Offline ledtester

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Re: Digital adjustable brick wall low pass filter
« Reply #2 on: August 23, 2019, 03:09:01 am »
For more discussion on aliasing, have a look at the section "SAMPLED DATA SYSTEM CONSIDERATIONS" from the MF-10 datasheet (p. 26):

https://www.ti.com/lit/ds/symlink/mf10-n.pdf
 

Online coppercone2

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Re: Digital adjustable brick wall low pass filter
« Reply #3 on: August 23, 2019, 03:58:48 am »
those digital smfilter chips usually have a clock noise spec some where.

I want to say LT used to sell the same chip or something based on the same die, so you can find the LT equivalent to see if its not there

it says clock feed through 5mVpp

they have continous time filters too, but the impedances tend to be high.
 


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