[Moved]: How to do AC analysis of LDO

[nagateja]

Hi,
i am working on LDO (Low Dropout Regulator). plese any one tell how to do AC analysis for basic LDo in cadence tool.
Please help me

 

[dick_freebird]

Re: How to do AC analysis of LDO

You can treat it as an op amp, which it basically is
(with an on-chip voltage reference tied to the +
input, and usually a way-asymmetric output stage,
and the feedback all internal).

Just put your AC=1 stimulus between the reference
and the error amp input, and proceed as normal.
I would recommend not bothering with trying to
break the feedback loop because that's not at all
like how the regulator would ever be run. Also you
care a whole lot about min and max headroom,
min and max load, min and max load impedance
(not necessarily the same thing), min and max
output C where an op amp is usually spec'd over
less severe application corners.

 

[chendong1017]

Re: How to do AC analysis of LDO

Hi all,

I have a problem when doing ac simulation.
If my LDO is 1V output voltage with 1mA current, which kind of output load should I use in ac simulation (HSPICE)?
1. Using a 1mA current source directly ?
2. Using a resistor with the value of 1kohm ?

Thanks.
CD

 

[arya.jagadeesh]

Re: How to do AC analysis of LDO

Hi all,

I have a problem when doing ac simulation.
If my LDO is 1V output voltage with 1mA current, which kind of output load should I use in ac simulation (HSPICE)?
1. Using a 1mA current source directly ?
2. Using a resistor with the value of 1kohm ?

Thanks.
CD

Hi,
If you are using current source then it will not effect the output pole position as the resistance of ideal current source is infinity but if you use resistor this will come in parallel with your output resistance and may effect output pole position. it is always better to use resistor from transients point of view as wel