LAUNCHXL-F28379D: Phase shift of sample-and-hold

Bui Van Linh

Intellectual 660 points

Part Number: LAUNCHXL-F28379D

Hello experts,

at the moment I am reading the blog of Dave Wilson

https://e2e.ti.com/blogs_/b/industrial_strength/posts/teaching-your-pi-controller-to-behave-part-vi

I can't understand the diagram of phase shift of a sample-and-hold in this blog.

The phase shift is caused by the delay time and you can calculate it very easily (see picture)

With a normalized frequency of 0.1 I have a phase shift of -36 degrees and not -18 degrees as the blog says.
where is my calculation error?

Thanks in advance - Bui

over 2 years ago

0 MatthewPate over 2 years ago

TI__Guru* 76060 points

Bui,

Please give us another day to respond. I am working to assign this to the correct engineer.

Best,

Matthew

0 Sira Rao80 over 2 years ago

TI__Mastermind 23920 points

Bui,

In the case of a sample and hold, phase is a linear function of frequency, as your equation shows. The plot is plotted to log scale, if it were in linear scale, we would see a straight line.

Normalized digital frequency (w) of 1 represents half the sampling frequency i.e. pi radians i.e. 180 degrees.

Therefore, normalized digital frequency of 0.1 represents 18 degrees.

Thanks,

Sira

+1 Bui Van Linh over 2 years ago in reply to Sira Rao80

Intellectual 660 points

Hi Sira, thanks!

Regards - Bui

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LAUNCHXL-F28379D: Phase shift of sample-and-hold