[SI-LIST] Re: FW: Need help on stability analysis
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 03 Jan 2014 03:23:03 -0800
Abinaya:
The SI-List does not support attachments. For general analog theory
questions there are probably better forums.
The gain never crossing 0dB, and the phase never crossing 180 degrees
suggests you have not swept a wide enough frequency range in your
simulations. All amplifiers have finite gain bandwidth products. And
all amplifiers develop increasing phase shift at high enough frequencies.
There are other stability criteria than just gain and phase margins such
as root locus methods. Any text on feedback and control systems should
provide you the help that you need.
Steve.
On 1/3/2014 3:09 AM, Abinaya Ramesh wrote:
> Hi,
> I have got few doubts while doing the stability analysis using bode plot.
> Below is the bode plot which I got from simulation tool.
>
> [cid:image003.jpg@01CF08A2.59A78A30]
>
> In the above bode plot, Gain is not crossing the zero values and phase is not
> crossing -180 degrees.
>
> How to find the phase margin if gain is not crossing the zero? In the same
> way , how to find the gain margin if phase is not crossing the -180 degrees?
> Could you please guide me in determining whether the system is stable or not?
>
> Thanks,
> Abinaya R
>
>
>
>
>
>
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