Fixed Point: cut, round, saturation?

Hi all,

I used to read FIR filter RTL implementation. I found they use a lot of
cut(i.e. delete several LSB bits) , round(i.e. delete several LSB
bits), and saturate to protect the data overflow.

I found they like to cut and saturate in the middle of the data path.
And round at the end of
the data path.

Is there any book talk about Fixed Point operation?
And is there any design tools?

Any suggestions will be appreciated!
Best regards,
Davy

Davy wrote:
> Hi all,
>
> I used to read FIR filter RTL implementation. I found they use a lot of
> cut(i.e. delete several LSB bits) , round(i.e. delete several LSB
> bits), and saturate to protect the data overflow.
>
> I found they like to cut and saturate in the middle of the data path.
> And round at the end of the data path.

that's noise shaping, i believe.

> Is there any book talk about Fixed Point operation?

there should be.  O&S has some theoretical analysis stuff.

Randy Yates has a web page someone.  i'm sure he'll be coming along
soon.  i don't know where it is and am too lazy to Google for it.  (try
it yourself.)

> And is there any design tools?

i thought there were.  MATLAB?  

r b-j

"robert bristow-johnson" <rbj@audioimagination.com> writes:

> Davy wrote:
>> Hi all,
>>
>> I used to read FIR filter RTL implementation. I found they use a lot of
>> cut(i.e. delete several LSB bits) , round(i.e. delete several LSB
>> bits), and saturate to protect the data overflow.
>>
>> I found they like to cut and saturate in the middle of the data path.
>> And round at the end of the data path.
>
> that's noise shaping, i believe.

It doesn't seem like we have enough information to conclude this,
Robert.

>> Is there any book talk about Fixed Point operation?
>
> there should be.  O&S has some theoretical analysis stuff.
>
> Randy Yates has a web page someone.  
---------------------------->???????

???

> i'm sure he'll be coming along
> soon.  i don't know where it is and am too lazy to Google for it.  (try
> it yourself.)

I'm not sure you're answering the question he's asking. 
-- 
%  Randy Yates                  % "Remember the good old 1980's, when 
%% Fuquay-Varina, NC            %  things were so uncomplicated?"
%%% 919-577-9882                % 'Ticket To The Moon' 
%%%% <yates@ieee.org>           % *Time*, Electric Light Orchestra
http://home.earthlink.net/~yatescr