[Discuss-gnuradio] Question on control-loop block design

[Ruben.Merz]

Hello,

I've been looking into the design details of the control-loop block. I stumbled 
upon the blog post of Tom 
(http://www.trondeau.com/blog/2011/8/13/control-loop-gain-values.html with the 
derivation 
https://static.squarespace.com/static/543ae9afe4b0c3b808d72acd/543aee1fe4b09162d0863397/543aee1fe4b09162d08633ac/1313345573084/control_loop_derivation.pdf)
 and also this article from TI: http://www.ti.com/lit/an/slyt169/slyt169.pdf.

Now looking at the schematics of the control loop in Tom's post and the TI 
article (figure 5), you notice a slight difference after the loop filter. In 
the TI article, there is delay (z^-1) followed by an accumulator. In the 
schematics of Tom's post, the delay block is directly integrated in the loop. 
Can somebody comment on these differences?

Thanks
Ruben