Step Response for cascaded filter & CIC filter

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cafukarfoo

Joined: 25 Jul 2007
Posts: 164
Helped: 3

27 Feb 2009 8:36 step response of cic filter

Hi Sir/Madam,

I had done an evaluation using
1. CIC filter with decimator factor of 128
2. CIC filter with decimator factor of 32 and 2 half band filter.

I am seeing the time needed for the filter to get stable is longer for option 2 above.

What i did is i run a step response for filter option 1 and filter option 2.

I attached the foils for your better understanding.

Can you let me know whether this is make sense? Thanks.

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FvM

Joined: 22 Jan 2008
Posts: 5152
Helped: 766
Location: Bochum, Germany

27 Feb 2009 9:29 cic filter step response

Quote:

I am seeing the time needed for the filter to get stable is longer for option 2 above.

It's the group delay of the FIR filter, according to the respective number of taps. Everything is normal operation. A suitable choice of filter characteristic depends on your application, which you didn't tell about.

cafukarfoo

Joined: 25 Jul 2007
Posts: 164
Helped: 3

27 Feb 2009 10:32 is a cic filter stable

Hi FvM,

I am using this filter to reduce the frequency sampling rate.

Do you think i can use different filter structure to reduce the group delay of the FIR filter?

For example, let's talk about a simple low pass 4 tap FIR filter and use direct form structure to implement this filter.

Is there any different if i use a serial multiplication and parallel multiplication? that mean for serial multiplication, i need to run 4 multiplication on 4 clock delay before i get a new output. And for parallel multiplication, i run 4 multiplication on each clock and output a new value on each clock.

Thanks.