akjyani
Newbie level 5
Hi all,
I am trying to do stability analysis for BGR (bandgap reference) circuit using iprobe in cadence virtuoso.
I am breaking the loop between opamp's output and gate of two PMOS transistors (as shown in attached fig).
when I am plotting loop gain and loop phase what I see is, loop phase is starting from 0 deg and then reaching to 90 deg (results are attached here). I have a doubt that generally loop phase should start from 180 deg to ensure negative feedback. I have attached the block diagram to explain how I am braking the loop and loop gain and phase results are also attached. When I see phase margin for this system I am getting around 85.3 deg.
Can somebody suggest why phase is starting from 0 deg not 180 deg ? Is this the correct method to do stb analysis for BGR? Any help will be appreciated.
Thanks in advance.
https://obrazki.elektroda.pl/9877215700_1505307702.png
https://obrazki.elektroda.pl/9272783800_1505307835.jpg
https://obrazki.elektroda.pl/4056930100_1505307846.jpg
https://obrazki.elektroda.pl/6579105700_1505307857.jpg
I am trying to do stability analysis for BGR (bandgap reference) circuit using iprobe in cadence virtuoso.
I am breaking the loop between opamp's output and gate of two PMOS transistors (as shown in attached fig).
when I am plotting loop gain and loop phase what I see is, loop phase is starting from 0 deg and then reaching to 90 deg (results are attached here). I have a doubt that generally loop phase should start from 180 deg to ensure negative feedback. I have attached the block diagram to explain how I am braking the loop and loop gain and phase results are also attached. When I see phase margin for this system I am getting around 85.3 deg.
Can somebody suggest why phase is starting from 0 deg not 180 deg ? Is this the correct method to do stb analysis for BGR? Any help will be appreciated.
Thanks in advance.
https://obrazki.elektroda.pl/9877215700_1505307702.png
https://obrazki.elektroda.pl/9272783800_1505307835.jpg
https://obrazki.elektroda.pl/4056930100_1505307846.jpg
https://obrazki.elektroda.pl/6579105700_1505307857.jpg