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Colpitts Oscillator simulation problem with PSpice.

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John_li

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colpitts oscillator pspice

Hi all,
I make a colpitts oscillator simulation with Pspice.But unfortunately it can not get reasonable result.It can not oscillate stably.I set C1,C2,C3,initial condition is 1V and L1 initail current is 1mA.Attach schematics and result FYI.Anyone kindly help me why not oscillate stabily?And How can i tune it?Thanks!

 

colpitts oscillator pspice simulation

You don't have enough loop gain to sustain oscillations. How did you calculate your C1,2 values?

When looking into the base with L disconnected you should see more than -10 Ohm Zin(real) for good oscillator startup.
 

    J

    John_li

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pspice simulation of colpitts oscillator

I set C1/C2=1/2~1/8,but still get the same result.Can you give me advice how to get Zin=-10 Ohm and C1 and C2?Thanks!
 

oscillator colpits simulation pspice

It is most probably a biasing problem. Make R2 (47k) and R4 (470-560) then it should work.
 

    J

    John_li

    Points: 2
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oscillator simulation spice

Follow your suggestion,I do it.The following is FYI.


 

pspice simulation of oscillator

I see now that you have your series LC values wrong. For series resonant with good Q use large L & small C (2.5mH & 0.1uF)

I now calculated the optimum values. R2 (56k) L1 (2.5mH) C3 (0.1uF) R4 (820)
C1 (33nF) C2 (47nF)

I will check on my simulator later but in theory it should work.

Added after 16 minutes:

Seems workable :D
 

    J

    John_li

    Points: 2
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colpitts oscillator problems

Dear E-design,
I do it as your done.But still the same,Is my setting wrong?Can you share me your source file to me?

Can you tell me how to set the initial condition is reasonable?
 

pspice colpitts

I have done nothing special. Just did a transient from 0-3mS with min time 0.01mS

What program are you using?
 

    J

    John_li

    Points: 2
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orcad 오실레이터

Thanks for your kindness.I use OrCAD 9.2.And I re-set the time:transient : 4mS and step :10us,i can get the result but i can not measure the frequency.and if i set the step:100us,nothing i can see.Can you share me how to select the component:C1/C2 value and Zin,and How to run optimum for oscillator?
 

simulation using pspice of colpitt oscillator

When I add a 500 Ohm load to R3 through a 0.1uF coupling cap like I did in the very first simulation the simulation results are almost identical.
 

    J

    John_li

    Points: 2
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colpitts oscillator in pspice

Thank a lt.Your kind suggest is very helpful to me!Can you give me more guidline about designing oscillator?For example,the negtive resister measure,the component selection...and so on.
Your result look perfect!
 

psice oscilator simulator

**broken link removed**

Includes all the math
 

    J

    John_li

    Points: 2
    Helpful Answer Positive Rating
colpitts oszillator pspice simulation

Thanks for your share!
 

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