Question on DT DSM to CT DSM transformation

[moorehuang]

Could anyone explain why in DT DSM to CT DSM transfer function transformation, DAC output shape(NRZ, RZ etc) is related?
As far as I am concerned, DT DSM also has DAC output shape like NRZ, RZ etc.

 

[moorehuang]

If anyone knows, please help.
Many Thanks!

 

[jgk2004]

I'm more a CT DSM designer, but I would think a DT DSM only has NRZ feedback...always... Since your feedback is switch cap and the DAC is in a way is just cap ratios.. Correct me if I am wrong. As for the transformation, you need to include in the mapping what DAC feedback you are using as in NRZ or RZ due to mapping DT to CT. I do all my mapping off of this paper see attached.

It is the most accurate way to do it.

Hope this helps

Jgk

 

[moorehuang]

But why in NTF expression, we cannot find any feature of the DAC output waveform? Such as (1-exp(-sTs))/s for NRZ.

 

[moorehuang]

Can anybody tell? For example, if the transfer function for DAC is D(s), in the feedback loop, the NTF should contain feature of D(s). However, it seems that the NTF calculation is just as ideal DAC feedback that D(s)=1?
Many thanks!