Common-base Collpits Oscillator

185

04:39:29

Update: Now working properly at approx. 50 MHz--thanks to hurz for help (see below).

published 11 years ago

hurz

11 years ago

The formula for a given inductor is the following: 1/(L*w^2)=1/(150nH*(2*pi*50MHz)^2)=67.55pF And a rule of thumb for the emitter cap is make it 10 times bigger 680pF and its quite nice oscillating at simspeed 10ns/s. Hope this helps.

KenSchwarz

11 years ago

Thanks! I just got this working on a breadboard with 1uH @ 10Mhz. Great to see the same waveform.

hurz

11 years ago

Yes, these collpits circuits do quite good match in reality. At this low frequencies of some mega Hz

KenSchwarz

11 years ago

Yes, your suggested values work with the simulator, but it seems choppy at this rate, so I'll leave the values as they were since they lend themselves to the animation. Thanks again for the tips!

hurz

11 years ago

Choppy probably because of an EC bug. If you turn the simu speed to much down in ones the timing gets chopped. Workaround is to restart the simulation at dialed target speed.

KenSchwarz

11 years ago

Yep, that did it. Now it's nice 'n smooth. Glad to see that the simulator doesn't run out of gas so easily...already paid for the year!

hurz

11 years ago

you have 680pF for both! The upper one suppose to be 68pF for 50MHz oscillation.

KenSchwarz

11 years ago

That's better...

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