Schmitt Trigger Sinewave Oscillator

165

02:35:43

It looks like that due to the hysteresis, the lower gain at higher frequencies, and the limited slew rate, this may work perfectly as a sinewave oscillator. The wave is not perfect, but no oscillator at 300kHz can produce absolutely perfect sinewave (maybe except a wien bridge oscillator).

published 10 years ago

hurz

10 years ago

A perfect sine wave generator does not exist! Also Wien is not perfect!

hurz

10 years ago

Ok, you already said this is not a perfect sine wave. Actually after measuring the THD by std method here on EC check how but all the harmonics look like ;-) http://everycircuit.com/circuit/5271481146146816

thebugger

10 years ago

I know nothing is perfect. Come to think about it, the term linear should not exist. There is always nonlinearities even in the most linear system. Even in a static quantum system there are fluctuations. This is believed to have happened at the beginning of the universe aka the big bang

thebugger

10 years ago

But hey 2% is kinda good. I think these 2% mostly come from the diodes. Anyway some oscillator topologies can have down to -140dB THD which can be considered to be the lowest THD an oscillator can have, so 2% is too much

hurz

10 years ago

I have never seen a sine generator better then 100dB and you say you can top that by a factor of !100! times then this? At around -110 thermal noise is dominating. How to get the rest 30dB or factor 30!? By increase to 30Vpeak...

thebugger

10 years ago

An ultra low distortion oscillator with THD below -140 dB - JanasCard search for that

thebugger

10 years ago

Actually search for ultra low distortion wien bridge oscillator. It's the first pdf file

thebugger

10 years ago

BTW i was also surprised to see such a low distortion oscillator, but it seems that it uses some very interesting PTC feedback to accomplish such distortions. I think i saw a phototransistor somewhere.

hurz

10 years ago

Nice link, but i still don't see how they got -140dB dynamic. They did something wrong in there calculations. Suppose a 100V sinewave output signal -140dB would mean all harmonics together are just 10µV!!!! Thats impossible!

thebugger

10 years ago

I don't get it too, but it seems like a legit article. But they measured 1uV average noise noise for 10V wave so i don't know, that's -140dB . They seem to have described every source of noise, and how they cancelled it, but i don't know. I like the Amplitude stabilization technique they used.

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