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Ring-oscillator Verilog A

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Saraparisa

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I designed 5-stage ring oscillator with CMOS inverter and it works perfectly as you can see in the attachment. I have no problem with that.
Then I replaced each CMOS inverter with Verilog-A inverter. Ring oscillator oscillates but something is weird with the output of each inverter. I have no phase shift?
What's the problem? what's the solution?

Screenshot of a ring oscillator with CMOS inverter '
https://obrazki.elektroda.pl/3407683500_1442646164.png


Screenshot of a ring oscillator with Verilog-A inverter '
https://obrazki.elektroda.pl/2662596100_1442646267.png
 

erikl

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A ring oscillator with an odd count of inverters will always oscillate, because of the 180° phase shift.

If you want to add phase shift to your Verilog-A inverters, perhaps this example could help, s. pp. 199 ff.
 

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