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An interesting yet incredibly simple RL oscillator I designed that closely resembles the classic RC astable multivibrator….
**shake to start**
In case you didn’t notice, there’s a few things that are quite different and peculiar about this design despite its unique simplicity if you examine some of the currents, and the voltage.
Here are a few characteristics that stand out:
1. You can’t build this with two individual resistors, it must share just 1 resistor in order to work. The main reason for this is because the transistors not only get turned on through the inductors, but also get cut-off through them via the two transistors 1 at a time in alternation. If two resistors are used, then there’s no way for the two transistors to cut-off current to each other.
2. You would think the resistor also limits the current in the whole circuit to a maximum of about: Vcc/R (theoretical maximum if you shorted the rest of the circuit to ground), which you’d expect to be a max of 5mA for a 5v supply in this example being simulated, but actually the currents in the inductors reach well over that, in fact more than 8 times the theoretical limit…. Which you’d think huh 😕! And honestly I still kinda find it fascinating cause I’m not too sure why or how that happens, but I’m assuming it’s got to do with negative resistance perhaps.
3. This oscillator can easily produce anything between 30 MHz and EVEN 1GHz! Although only that high seen in simulation so far (and actually even up to 2GHz; so exactly 2x whatever the frequency at the shared resistor node -which makes sense if you consider that the current has to carry 2 periods of oscillations for every half cycle at that point)
4. This oscillator will even work with very low supply Voltages since it’s using inductors for feedback and has very low voltage drops. (even below 700 millivolts; at slightly lower frequencies)
Update:
Unfortunately it does not seem to oscillate as fast as I though a breadboard though :( Could reach up to 110MHz. However, if you can make small enough inductors, and the transistors you use have a high enough Tf, then I still believe it can oscillate much faster, may have to adjust the resistor, but typically higher values mean higher frequencies but lower gain, so it can’t be too high at VHF-UHF frequencies
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