AC sim convergence issue

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analog_chip

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Hi, I am simulating a long chain of 40 delay cells. Each cell consists of one all pass delay cells and a buffer. There is a coupling cap between buffer and delay cell. Each unit cell has unity gain. After 30 stages the ac gain shows rough peaks showing convergence issue. I see a zig-zag curve instead of smooth one. How to fix this issue? Please help.
 

AC (small signal) analysis doesn't use iterative solver, don't see how convergence problems should be brought up. I rather guess it's a numerical resolution problem and too few frequency points. How much is the magnitude ripple? Can you show a plot?
 

What kind of simulator are you using? Cadence Spectre AC simulation can confuse when the ground of the input source is else then device model grounds.
 

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