Timeline for MOSFET ring oscillator LT SPICE
Current License: CC BY-SA 4.0
7 events
| when toggle format | what | by | license | comment | |
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| Dec 7, 2023 at 18:55 | vote | accept | the_circuit | ||
| Dec 4, 2023 at 14:32 | comment | added | V.V.T | You can use simulations to build up your intuition. Examine CMOS inverters: how the inverter's VTC depends on NMOS/PMOS sizing and what are the resulting waveform shapes; run tran analysis simulations with a large-signal sine wave fed to the inverter input and how the output signal changes with frequency, etc (small signal analysis is of little use here). The plots you receive in this simulations are worth a million words. | |
| Dec 4, 2023 at 14:31 | comment | added | V.V.T | Unlike, say, the case of Wien bridge oscillator, there exist no compact formulas suitable to describe the MOSFET ring oscillator behavior -- simply because the Wien bridge oscillator is basically a quasi-linear circuit with a small non-linearity introduced to provide automatic gain control, whereas the MOSFET ring oscillator is essentially a non-linear circuit. | |
| Dec 4, 2023 at 14:31 | comment | added | V.V.T | The MOSFET ring oscillator is not a weapon of choice to generate a periodic waveform free of higher harmonics; it cannot and, in fact, never does generate either a pure sine wave or a pure square wave. The generated waveform is shaped by a complex interplay of the CMOS inverter's voltage transfer curve and non-linear MOSFET capacitances. | |
| Dec 4, 2023 at 4:02 | comment | added | Ste Kulov |
@spiderman19 It may not be easily seen, but another thing the simulation in this answer does differently is it properly connects all the MOSFET pins. In your schematic screenshots the nmos4 and pmos4 symbols are connected incorrectly. Your body nodes are all floating. It's difficult to see because the dark blue and light blue look so similar but it's there. Pull up the SPICE error log (CTRL+L) post-simulation to confirm. Either draw it like in this answer or any other way where you don't get a floating node warning in the log. In general, avoid going "through" dark blue lines.
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| Dec 4, 2023 at 0:46 | comment | added | the_circuit | thank you. I was able to get the oscillation to start but I have a doubt about the shape of the waveform. I noticed that it is shaped like a sinusoid but in some cases the square shape is retained. Do you know what changes the shape of the waveform from a sin to a square? | |
| Dec 2, 2023 at 8:57 | history | answered | V.V.T | CC BY-SA 4.0 |