[SOLVED] why oscillator 100 mhz that it test in practical ,in simulation in orcad dosn't work

[stackprogramer]

why oscillator 100 mhz that it test in practical ,in simulation in orcad dosn't work


i test three osc other they dont work???
its possible that i simulate osc 100 Mhz in orcad??
the file simulation orcad for this circuit

 

[stackprogramer]

thanks very much for replay,when i do'nt set (skip initial transient solution)the image response is

when i set (skip initial transient solution) according your talk image response is

for inductor value i test 1 uH till 100 H.for 10 H is best,
why wave not continue???????please help me,i am confused!:???:

 

[FvM]

I'm not motivated to download files from an external server, so I didn't look into the simulation files.

Most likely reason, the oscillator misses a kickstart after initial transient solution.

Trivial workaround: run the simulation with UIC option activated (skip initial transient solution). Presumed that you selected a reasonable inductor value (not shown in the schematic).

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The circuit can't oscillate with too large inductor values. It's designated as "FM" modulator, so the inductance should be in a 100 nH range. It may be necessary to enforce a small simulation timestep, e.g. 1 ns.

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Although the circuit can work, the DC bias point is far from optimal with usual 2N3904 current gain. There should be a base voltage divider, e.g. 10k parallel to the 1nF capacitor.

 

[stackprogramer]

thanks very much for step size 1 ns in (Time domain analysis) it image response is

i have a puzzle,when i plot in 10 ns second we have oscilate
when i set to 1 s,we have not oscilate ,for practical the oscilate is for ever,
why orcad can n't plot sine wave in 1 sec?!!!!does n't it means the wave after 1 second is damping!!!!!??????
if not,then its true,

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thanks,i change step to 100ns its image show sinwave is damping!???

i add R=10 k to 1nF capacitor in base transitor the response image not change and sinwave is damping!!!!!

how in real world it works????

 

[FvM]

When using UIC option, the oscillator doesn't start before the base bypass capacitor has been charged. You can speed it up by setting an .IC condition for the base voltage.

If the circuit parameters are inappropriate, no oscillation may occur. But with e.g. 100 nH inductance, the oscillator should work.

 

[stackprogramer]

Dear FvM thanks very much,your reply is best.my problem solved.:thumbsup:

 

[stackprogramer]

Hi my friend ,i created this oscillator,i get grade 20/20.i share picture and files simulation this oscillator.
picture oscillator

result on oscilloscope

picture mixer with ic mc1496p

files is shared on github
https://github.com/stackprogramer/Exp-Electronic-3