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I got a filter coded by Verilog, which it implemented with 2 cascaded
accumulators. Someone told me it does work, but I can't figure it out. Can
you help me ?

The input of the first accumulator is a bit stream, and the input of the
second accumulator is the result of the first accumator. Accumulation
period of the filter is 512 bits.

e.g.
input: 0 1 0 1 0 1 0 1 0 1 0 1...
output of the 1st accumulaor: 0 1 1 2 2 3 3 4 4 5 5...
output of the 2nd accumulaor: 0 1 2 4 6 9 12...

If the filter only include the first accumulator, It's an average filter,
but when combined with the 2nd accumulator, what is it? When simulated
with Matlab, the 2 stage accumulator doesn't give better performance. And
it seems to have some obvious problems, i.e. the first bit of every
accumulation period has a very large effect on the output and starting
accumulation with 0 or 1 would make the result quite different.

Is it a correct filter? What is its frequence response? Thank you!  

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Brian_zhong wrote:
> I got a filter coded by Verilog, which it implemented with 2 cascaded
> accumulators. Someone told me it does work, but I can't figure it out. Can
> you help me ?
> 
> The input of the first accumulator is a bit stream, and the input of the
> second accumulator is the result of the first accumator. Accumulation
> period of the filter is 512 bits.
> 
> e.g.
> input: 0 1 0 1 0 1 0 1 0 1 0 1...
> output of the 1st accumulaor: 0 1 1 2 2 3 3 4 4 5 5...
> output of the 2nd accumulaor: 0 1 2 4 6 9 12...
> 
> If the filter only include the first accumulator, It's an average filter,

Only when its count is divided by the number of inputs.

> but when combined with the 2nd accumulator, what is it? When simulated
> with Matlab, the 2 stage accumulator doesn't give better performance. And
> it seems to have some obvious problems, i.e. the first bit of every
> accumulation period has a very large effect on the output and starting
> accumulation with 0 or 1 would make the result quite different.
> 
> Is it a correct filter? What is its frequence response? Thank you!  

Brian,

Asking three times won't get you more answers than asking once. You need 
to give more details before anyone can comment on your filter. What do 
you want it to do? How would you know if the performance were "better"? 
Is the filter modeled on something, or did you invent it? (does the 
first accumulator count bits -- "The input of the first accumulator is a 
bit stream" -- or does it add numbers, as the second must? ...

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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On Thu, 26 Jan 2006 12:32:43 -0500, Jerry Avins <j...@ieee.org> wrote:

  (snipped)
>> 
>> Is it a correct filter? What is its frequence response? Thank you!  
>
>Brian,
>
>Asking three times won't get you more answers than asking once. You need 
>to give more details before anyone can comment on your filter. What do 
>you want it to do? How would you know if the performance were "better"? 
>Is the filter modeled on something, or did you invent it? (does the 
>first accumulator count bits -- "The input of the first accumulator is a 
>bit stream" -- or does it add numbers, as the second must? ...
>
>Jerry
>-- 

Humm,  two accumulators cascaded huh?

I wonder if this is part of a multi-stage CIC filter (?)

[-Rick-]

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Rick Lyons wrote:
> On Thu, 26 Jan 2006 12:32:43 -0500, Jerry Avins <j...@ieee.org> wrote:
> 
>   (snipped)
> 
>>>Is it a correct filter? What is its frequence response? Thank you!  
>>
>>Brian,
>>
>>Asking three times won't get you more answers than asking once. You need 
>>to give more details before anyone can comment on your filter. What do 
>>you want it to do? How would you know if the performance were "better"? 
>>Is the filter modeled on something, or did you invent it? (does the 
>>first accumulator count bits -- "The input of the first accumulator is a 
>>bit stream" -- or does it add numbers, as the second must? ...
>>
>>Jerry
>>-- 
> 
> 
> Humm,  two accumulators cascaded huh?
> 
> I wonder if this is part of a multi-stage CIC filter (?)

Very likely, but we have a language problem. Bit, byte; who cares? I 
won't get very far without the ability to make such distinctions.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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"Jerry Avins" <j...@ieee.org> wrote in message 
news:E...@rcn.net...
> Rick Lyons wrote:
>> On Thu, 26 Jan 2006 12:32:43 -0500, Jerry Avins <j...@ieee.org> wrote:
>>
>>   (snipped)
>>
>>>>Is it a correct filter? What is its frequence response? Thank you!
>>>
>>>Brian,
>>>
>>>Asking three times won't get you more answers than asking once. You need 
>>>to give more details before anyone can comment on your filter. What do 
>>>you want it to do? How would you know if the performance were "better"? 
>>>Is the filter modeled on something, or did you invent it? (does the first 
>>>accumulator count bits -- "The input of the first accumulator is a bit 
>>>stream" -- or does it add numbers, as the second must? ...
>>>
>>>Jerry
>>>-- 
>>
>>
>> Humm,  two accumulators cascaded huh?
>>
>> I wonder if this is part of a multi-stage CIC filter (?)
>
> Very likely, but we have a language problem. Bit, byte; who cares? I won't 
> get very far without the ability to make such distinctions.
>
True - could be part of a 2nd order sigma-delta modulator  - not enough info 
to guess frequency response of the whole thing if it is.

Best of Luck - Mike

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