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frequency stability (Read 1588 times)

raja.cedt

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Germany

frequency stability
Sep 30^th, 2008, 3:39am

hi all,
i have basic doubt regarding Frequency compensation.
Normally when amplifiers in the loop are very fast means they give less phase shift, so more stable.But when we do dominant pole compensation intensionally we reduce the pole frequency means we are making system slow hence system became stable with slow amplifiers..can you explain whats wrong in that.
THANK YOU

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Berti

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Re: frequency stability
Reply #1 - Sep 30^th, 2008, 4:04am

I think you completely misunderstand frequency compensation / pole splitting.

For a system to be stable you need sufficient phase-margin.
1 pole shift the phase by 90 degree.
2 poles shift the phase by 180 degree.

Since an amplifier has more than 1 pole, you need a first dominant pole at
low frequency to make sure that the gain is low (typically <0dB) at the frequency
where the second pole comes into play (in shift the PM by another 90 degree).
This can is the purpose of compensation.

Regards

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