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1,343. Location. USA, midwest. Activity points. 9,749. Agree with Braski. Generally you talk about phase margin when your feedback loop reaches a gain of zero. You want to maintain some positive phase margin at that point, such that you have "room to push/pull" in your feedback loop. Mar 8, 2011.
6. Reaction score. 4. Trophy points. 1,288. Activity points. 1,477. phase margin in cadence calculator. Run AC analysis, View waveform of gain and phase then measure phase at 0dB gain this will give you the phase margin. 60º phase margin upto about 180º is considered stable.
Thats all. For finding the phase margin, you have to identify the phase ot 0 dB loop gain. Whe the phase is 25 deg less than -360 deg - the PM is 25 deg. Absolutely, the following is understood (The phase of the loop gain must start at -180 deg for negative feedback (when the phase inversion within the loop is taken into account).
2,208. hspice .meas ac .measure ac gain. You can try. .measure ac min_phase MIN vp (out) from=1 to=ugain_freq. The phase_margin is, then, min_phase- (-180): .measure ac phase_margin = param ('180+min_phase') regards. selvaraja. selvaraja.
7,788. Re: Phase margin. It can be proved as a general case that given a phase margin of 60° the amplifier's step response will not have any peaking, thus very less possibility for it to become stable. Thus 60 degrees is normally chosen to be the phase margin. 45° degrees is taken as a tradeoff, to have faster risetime and less settling time.
Advanced Member level 1. I am measuring phase margin for this bandgap using iprobe from analogLib in Cadence by breaking the loop and inserting iprobe between the output of op amp and gate of two top transistors. However, the problem is that I have heard that this method doesn't work for circuit that has more than one loop.
Bangalore, India, India. Activity points. 4,334. The Phase margin should not affect the DC gain at all. The better the phase margin, you would see less ringing at the output with step inputs. 45° is a good number. I used to check for the differential input to differential output. Aug 5, 2013. #3.
In contrast, a margin of only 20 deg will be connected with a step response that exhibits ringing and a heavy overshoot of app. 20%. 4.) That is the reason, we require - if possible - a phase margin of at least 60deg. for good stability and sufficient time behaviour. anhnha.
7. Trophy points. 1,298. Activity points. 2,350. increasing phase margin. Hi. You should decrease frequency of the dominant pole. this change decreases your unity gain BW, but increases your phase margin.
Total current=150uA. Vpn:Vnn= 0- 0.9V. Phase Margin: >45deg. Gain: >60dB. At this point, my design is embarrassing. I can only get the voltage up to 50dB. And the phase margin is worse -39deg. I know that the A= Gm Rout. and to improve Gm: I have to increase the W/L or/and I of the input stage.