CIC filter for sigma-delta converter

Hi,

I have one question about the implementation of a CIC decimator filter.
How I can meet my especifications of a output range of 16 bits in the CIC
filter output? I have a 2nd order sigma-delta modulator that has a bit
stream (1 bit output). Can anyone give me some information about this? The
best informations is a CIC filter RTL with explicit one bit input and
explicit 16 bits output. I don't have idea how 1 bit input it will become
a 16 bit output by a CIC decimator filter.

Sorry about my english, is not my primary language and thanks for help.

Brito.

PS: my downsampling rate is 256.

On Sun, 25 Nov 2007 18:51:43 -0600, ultralowpower wrote:

> Hi,
> 
> I have one question about the implementation of a CIC decimator filter.
> 
> How I can meet my especifications of a output range of 16 bits in the CIC
> 
> filter output? I have a 2nd order sigma-delta modulator that has a bit
> 
> stream (1 bit output). Can anyone give me some information about this? The
> 
> best informations is a CIC filter RTL with explicit one bit input and
> 
> explicit 16 bits output. I don't have idea how 1 bit input it will become
> 
> a 16 bit output by a CIC decimator filter.
> 
> Sorry about my english, is not my primary language and thanks for help.
> 
> Brito.
> 
> PS: my downsampling rate is 256.

You need a deeper knowledge of what is going on if you want to have a hope
of actually making things work -- blindly dropping someone else's little
bit-o-algorithm into your design is just a recipe for confusion and
failure.

Basically, all you have to do is make your data paths wide enough to
accommodate your desired precision, and pay attention to scaling.  If you
take your one bit of data, give it a weight of 2^16, and run it through
filters that have 16 bits of precision and unity gain at DC, then you'll
find that your output data will be 16 bits wide just as you want.

-- 
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html