Stats

  • Locked Locked
  • Replies 11
  • Subscribers 126
  • Views 17390
  • Members are here 0
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Can the stb simulation in Spectre calculate the negative phase margin?

zuiying

When I was simulating a two-stage op amp, I tried to use stb to simulate its stability.

 At first I did not add a compensation capacitor (later I used ac simulation and the calculator to find that the phase margin at this time was a negative value).The stb simulation shows "PM metric not found".

And when I added the compensation capacitor, the stb simulation showed the phase margin.

Therefore, can the stb simulation only calculate the positive phase margin, and the negative phase margin will be considered "PM metric not found"? (If this is the case, then I may prefer to use ac simulation and calculators in the future.)

Thank you very much.

Parents

  • I just had a look at the documentation and discovered that there is a (new?) parameter margininfo_unstable with the default value "no". So you will probably get a result if you set margininfo_unstable=yes.

  • in reply to Frank Wiedmann
    Frank Wiedmann said:
    I just had a look at the documentation and discovered that there is a (new?) parameter margininfo_unstable with the default value "no". So you will probably get a result if you set margininfo_unstable=yes.

    I'd not spotted that new parameter. It was added in SPECTRE19.1 ISR9 for precisely the scenario described here - outputting the margins when the circuit is unstable. I've not tried it, but that does appear to be the way to do this.

    Andrew

Reply
  • in reply to Frank Wiedmann
    Frank Wiedmann said:
    I just had a look at the documentation and discovered that there is a (new?) parameter margininfo_unstable with the default value "no". So you will probably get a result if you set margininfo_unstable=yes.

    I'd not spotted that new parameter. It was added in SPECTRE19.1 ISR9 for precisely the scenario described here - outputting the margins when the circuit is unstable. I've not tried it, but that does appear to be the way to do this.

    Andrew

Children
No Data

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.