• Locked Locked
  • Replies 2 replies
  • Subscribers 38 subscribers
  • Views 949 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

gain and phase margin

brian9587
Prodigy 30 points

Hi,

I am new to this tool. The gain and phase margin are displayed as numbers in the what if analysis. However, i am more interested in knowing how to read to gain and phase margin from the plot/curve.

There are 4 gains and 3 phase curves. Is compensated error amplifier gain the loop gain? Which curve should i be looking at to get the f0db and f180?

Thank you very much.

  • Prodigy 30 points

    Hi brian,

    I have been facing this problem ,as well that the cursor function which was present in the swift designer tool v3.1 is not present here,which makes it more difficult to read the graph and the markings are not visible as well.The loop gain is I feel the the total gain considering the it is the sum of the comp amplifier gain and the power stage gain,while the crossover frequency(s) can be read from the total phase,though the markings are not clear

     

  • TI__Intellectual 1280 points

    To read gain and phase margins from the chart directly, it's easier if you turn off the curves except for Total Gain and Total Phase. 

    Find the place where the gain crosses over zero db.  Move up the chart until you see where the phase curve intersects that freq.  Using the markings on the right side of the chart for the degrees of phase margin.  You should be in the area of 30 - 60 degrees of phase margin for stability.  To find the gain margin you must find the frequency where the phase curve crosses the zero degree mark.  Move down the chart to see where the gain curve intersects that freq.  use the markings on the left side of the chart to find the correct Decibel level of gain margin, (Note Gain margin will be a negative value)  It's recommended to have at least -10dB of Gain margin.  I hope this helps.  Also it's a bit harder to do this on the what if page because if you scale the chart there is a bug that removes the frequency markings from the bottom of the chart so you just have to know which line is which freq (at this point in the software development the frequency axis is always at the same fixed range of values)