This is a pseudo-mirror of www.bores.com DSP intro at http://www.bores.com/courses/intro/iir/5_form2.htm [sic] as per the policy of this site.
This mirror was created from the source on 03/08/2000 at 22:46 Central Time.
Commercial information, time-dependent information, and all the damn JAVA scripts have been removed. All "htm" extensions have been changed to the proper "html" extensions. Has also been edited for
coherence, proper-linkage, and better document flow.
Copied without permission.
The filter diagram for direct form 1 can be drawn direct from the filter equation:
The block diagram is in two halves: and since the results from each half are simply added together it does not matter in which order they are calculated. So the order of the halves can be swapped:
Now, note that the result after each delay is the same for both branches. So the delays down the centre can be combined:
This is called direct form 2. Its advantage is that it needs less delay elements. And since delay elements require hardware (for example, processor registers) the direct form 2 requires less hardware and so is more efficient than direct form 1.
Direct form 2 is also called canonic, which simply means 'having the minimum number of delay elements'.
| Last updated: 4th January 1998 | http://www.bores.com/courses/intro/iir/5_form2.htm