What is making the Rosmary circuit oscillate when the gate input is negative?
GL.
I've tested this in SPICE, and I can get indefinite oscillation by giving it a single pulse from 5V to 0V. (I think Hum did too). What's making this thing oscillate? Here's a possibility: Barkhausen criteria for oscillation: 1) The circuit requires gain. 2) The circuit requires a feedback mechanism, and the feedback must be in-phase. 3) The circuit forward and feedback gain product must be 1. 4) Not a requirement for oscillation, but usually some limiting mechanism is required to stabilize the amplitude. 1a) The MOSFET switch (any active switch really) is really just an amplifier with a lot of gain. In this case, a common-source amplifier. 2a) MOSFETS are notorious for exhibiting huge inter-electrode capacitance. Like any amplifier, the Common-source amp has it's bandwidth limitation, and this is largely due to the parasitic capacitance between the electrodes, in particular from Drain to Gate (whose effect is multiplied by the gain, i.e. Miller effect). 3a) If at the unity-gain frequency the phase is changed from 180º to 360º, then you now have all the ingredients required to create a self-sustained oscillation from a "simple" amplifier. 4a) In this case, I believe the limiting mechanism is either from the body diode partially conducting, or it's the quadratic V GS to I D relationship. At any rate, that's my take so far from the testing I've done. .99
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