Hi Dewster,
That is a lovely oscillator!
I have just run it on my simulator using my 74HCU04 "analogue" model (which I constructed from the schematic and used the best transistor models I could find) and with 5 in series, it runs superbly.. (a minimum of 3 are required to get enough gain - but with 5 the gain is more accurately defined by the input and feedback resistors)
I also ran it at supply voltages from 3 to 5, and with non-ideal inductors (series resistances up to 3 ohms (simulation crashed at 4 ohms) and its great - low current (peaks < +/- 150uA at 5V, < +/- 80uA at 3.3V) great antenna voltages (~50V P-P @ 3V3, ~70V P-P @ 5V)
I think you are right when you say "this one looks like a keeper!"
Congratulations!
Fred.
(this oscillator has a superficial resemblence to the Lev oscillator, but I dont think there is much real similarity - I might be wrong though..
I cant get my head 'round it right now, but I wonder what the effect would be of coupling L1 and L2.. On the Lev oscillator, this coupling hugely increases the total series inductance of the tank, and yet allows the antenna resonator to act on only one section of this inductance - but I will certainly play with coupling just to see what happens ;-)
ADDED ->
Been probing the waveforms and understanding the operation better.. the more I see, the more I like it - its so clean! .. I think your use of capacitive potential divider for the input tapping is one of the things that turns the quite crude "open" oscillator into a something special - well, actually, theres a lot of things that you have done that transform this design... With the 3k3 resistors, a simple discharge tube on the antenna should provide adequate ESD ptotection - Yeah! Its a cracker!
Its actually different enough to anything I have seen that I think you have full right to "ownership" of it.. Certainly the best simple CMOS oscillator I have ever seen! - Oh, I have absolutely no doubt that it will work as well or better than the simulations.
Using 5 CMOS inverters, 1 ohm per inductor, and 5V supply, all other components unchanged, I got 1.378MHz with 10pF antenna C, and 1.4284MHz with 9pF, about 50kHz/pF
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Ok, playing with values etc, I think this oscillator is better for digital applications than for analogue - I think (not sure) that when two inductors are used, there is a slight increase in near-antenna sensitivity - the antenna LC I think is working to "amplify" the effect of the antenna C which is in || with the L1 -- divider C.. Only marginal, but the wrong bias for heterodyning -> audio. Using only one inductor one gets back to a simpler relationship, but lose some of the antenna amplitude. To optimise this oscillator for analogue audio the Lev topology would probably be better..
But this was designed for digital, and for that its great - Without the 2nd L, its still a good oscillator for analogue - better and simpler I think than some of the standard oscillators like those in the SC theremins - but I need to build it to be sure.