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It's Hard to Build an Oscillator

It's Hard to Build an Oscillator

3 comments

·November 21, 2025
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eternauta3k

I was hoping this would go more into startup and amplitude control, which are for me the tricky parts of building a phase shift oscillator (because you have to analyze the non-linear behavior).

I guess hobbyists nowadays are just using SI5351 and calling it a day.

atoav

Coincidentally I thought a class of art students just yesterday how to build oscillators. And it is not hard at all. Take a logic inverter IC (CD40106 Schmitt-Trigger Hexinverter) pick a single gate, connect the output to the input, add a capacitor from the input to ground. That is it. Three parts and you got a Relaxation Oscillator. And then you have 5 inverter gates left.. But of course one could argue ICs are cheating, since any PLL-IC would have an oscillator onboard.

Why the first two circuits fail is also pretty obvious without derper circuit analysis: to get reliable oscillation you don't only need amplification, you also need some time setting element, usually in the form of a capacitor (or involuntary capacitance).

eternauta3k

Relaxation oscillators are easy, good phase shift oscillators are an art.