Sine Wave Getting Distorted In Colpitts Oscillator Circuit

Thread Starter

DD Ki Vines

Joined Apr 20, 2019
5
Today I Created a basic Colpitts Oscillator Circuit using 2n3904 npn transistor the circuit diagram is given in attachments and when I saw the output I got a Distorted sine wave.I haveu 2,1nF acitors and a1mH inductor as the tank circuit and a 0.1uF c is used to fed back output signal to the base of the transistor.IMG_20190915_120345.jpg Now the interesting thing is though the output sine Wave is distorted,the input sine Wave looks fine(yellow waveform is input and purple waveform is output)IMG_20190915_120812.jpg IMG_20190915_120848.jpg .Please help me getting over this issue and it would be great if someone explains me why this is happening
 

ci139

Joined Jul 11, 2016
712
thanks for translation TK ~\ -.-

Modified the osc circuit to lesser distrotion (i donno if it's Colpitt's or not)
about ::
 
Last edited:

Danko

Joined Nov 22, 2017
792
circuit-20190915-2346.png
EDIT:
Please help me getting over this issue and it would be great if someone explains me why this is happening
It is right, good behavior of oscillator, because tank continuously loses energy, but transistor, every period, adds new portion of energy.
Due to high (about 100) gain of transistor, that portion of energy is too big and forms step in bottom of sine.
Problem can be solved by placing resistor between emitter lead and ground.
Picture above shows good sine, when gain of amplifier is about 3 (10k / 3k).
 
Last edited:

ci139

Joined Jul 11, 2016
712
why this is happening
the question is always "what (is it)" or "where (there is - it is so)" . . .

as the Base is apx. at the same phase with the Emitter -- your 100nF allows at favorable conditions the LC tank to "discharge"

Basic - Osc - TEST - A-0_grd.gif
((( I.C2 has spikes /// I.C5 has -90deg rotated Z-s )))
Basic - Osc - TEST - A-0_plt.png
___________________
fuzzy//"intuitive" Quick fix (( C4 is not verified to make it better -- was added in a hope it improves the transit of the neg. half-cycle ))
? but it might have a jitter in it ( or might be due th pixel-quanted PC-display ) ?
Basic - Osc - TEST - A-01.png
 
Last edited:
Top