| Author |
Message |
ahmad_ee
Joined: 01 Dec 2005
Posts: 10
Helped: 1
|
 13 Sep 2008 21:10 dpll iir |
|
|
|
|
Hi All,
In an all digital PLL, with the loop filter as an IIR filter, when transforming the design to fixed point the loop filter was found to need a large number of fraction bits to keep the performance, although this large number is not required by the DDS input !!
Is it regular for that filter to need so large number of bits, I thought it would due to being an IIR and so memorizes the signal from so many cycles in the past !!
Regards,
|
|
| Back to top |
|
 |
Google
AdSense
|
13 Sep 2008 21:10 Ads |
|
|
|
|
|
|
| Back to top |
|
|
ylscqu
Joined: 20 Dec 2003
Posts: 46
Helped: 1
|
14 Sep 2008 3:41 Re: IIR filter for DPLL loop filter |
|
|
|
|
round off or something like truncate can solve this problem.Who can provide
some example?thx
|
|
| Back to top |
|
|
zorro
Joined: 06 Sep 2001
Posts: 380
Helped: 47
|
16 Sep 2008 16:57 IIR filter for DPLL loop filter |
|
|
|
|
Hi Ahmad,
tuncation produces dc-residual, that is a special case of limit cycle.
For instance, in a type-2 loop you can have a non-zero steady state phase error, althougt in that type of loop one intends to have zero error.
How is your filter, and which is the loss of performance?
Regards
Z
|
|
| Back to top |
|
|
