Multisim and Ultiboard

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CMOS ring oscillator not oscillating

I'm a student who is very new to multisim so please have a  little patience with my lack of know how.


I have built a CMOS Ring Oscillator in order to measure the frequency of oscillation to the number of inverters used and would now like to compare my measured results to a SPICE level 1 simulation.


In my real-life circuit I used inverters found on the CD4007 chip, set a pulse generator to 50Khz moving from 0V to 5V and fed this to the ring. I then turned a switch connecting the pulse generator to the circuit off and viewed the oscillations on an oscilloscope. I was getting a value of about 4.14MHz for the 3 Inverters found on the schematic.


The problem is, when i set the circuit up in multisim and measured voltage from the probe at the 3rd inverters output,  the ring is not oscillating.


With transient analysis and oscilloscope readings the output of the ring oscillator only changes with the pulse of the generator. If i open the switch it keeps oscillating at this frequency. My questions are as follows...


i) Is the circuit set up correctly for the purpose of this experiment?


ii) Will i need to add resistors to emulate load resistance?


ii) Should transient analysis be used or am i better off using an oscilloscope?


iii) Should a single pulse be used instead of a switch? Or both? If other please specify how this is done.


Note** Accoring to the question found here:

the issue was that i hadnt set up an initial conition. I have tried setting the input wire to the 1st inverter to be 0V and 5V but neither helped.



Thanks in advance for any replies Smiley Happy


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I was having the same problem, but it was resolved once I set an initial condition for the net. Double click on one of the input or output wires (I did for the 1st input wire) , then go to 'Simulation settings' tab and check the box saying 'Use IC for transient analysis'. 


If you did this and it still did not help then maybe the problem is in your design. Check the capacitor values and the MOSFET models you used 

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