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pz analysis & stb analysis problem

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ljy4468

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stability and pz analysis

Hi
I've a question about pz & stb analysis of ADE.

First, I've designed LDO(low drop out regualtor) with amplifier.
Then I anlysis stability of LDO with 'iprobe' & stb analysis.
That is ok. (loop phase & gain plot OK)

But When I perform pz analysis,
There's an unmatch point between pz & stb analysis.
(In pz, I choose input source as positive input of amplifier.)

For example, In stb plot, -3db freq. is 50kHz.
But in pz plot, first pole is 100kHz.

what is wrong with that??

Regards.
 

how to perfrom p/z plot

ljy4468 said:
Hi
I've a question about pz & stb analysis of ADE.

First, I've designed LDO(low drop out regualtor) with amplifier.
Then I anlysis stability of LDO with 'iprobe' & stb analysis.
That is ok. (loop phase & gain plot OK)

But When I perform pz analysis,
There's an unmatch point between pz & stb analysis.
(In pz, I choose input source as positive input of amplifier.)

For example, In stb plot, -3db freq. is 50kHz.
But in pz plot, first pole is 100kHz.

what is wrong with that??

Regards.
Click to expand...
I have designed a LDO and when I performed the pz analysis, I added the ac signal to the reference voltage net. and then i can check the output file and check it.
Click to expand...
 

pz plot

I have two comments:

1.) I assume you have performed the stability check with an open loop and the pz analysis with the loop closed, right ?

2.) In general, for a system of an order >1 the 3-dB-frequency is NOT equal the pole frequency
 

schematic example pz analysis

There are more chances of first doubt turning into reality...!
 

For my opinion, this kind of comment does not really help.
LvW
 

I checked STB in closed loop configuration.
(break the loop and place iprobe )

And LvW,
at 3db freq, there must be pole or zero.
So loop,phase curve roll off. Isn't it??

I'll show you detailed schematic, simulation plot

Thanks
Regards.
 

    V

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