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[Moved]: Colpitts Generator Pspice

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arek462

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Hello!

I tried simulate colpitts generator from Horowitz's book:



I use free version so i had to replace crystal:



Unfortunately transient simulation doesn't work like i expected:



So if some expert could tell me how make it work correctly, i will be grateful.

Thank you!
 

Re: Colpitts Generator Pspice

LvW said:
....... so i had to replace crystal with.....?
Click to expand...


Replaced it with RLC circuit, but i now i have problem with "floating node". Could you help me?

 

Re: Colpitts Generator Pspice

Hi,

the node around R7 are completely coupled by capacitors. Maybe therefore the simulator can not find the DC operation point.
--> Try to connect a 1G resistor from R7 to GND.

Klaus
 

Re: Colpitts Generator Pspice

Thank you!

I added resistor and the floating node is gone. Howewer circuit still doesn't work like i expected. Please help

 

Re: Colpitts Generator Pspice

arek462 said:
Thank you!

I added resistor and the floating node is gone. Howewer circuit still doesn't work like i expected. Please help
Click to expand...

In a Colpitt oscillator the crystal works as an inductor only.
Hence, you should use a simple inductance of a suitable value - depending on the desired oscillation frequency, of course.
(and you will have no problems finding a DC operating point).
 

Re: Colpitts Generator Pspice

LvW said:
In a Colpitt oscillator the crystal works as an inductor only.
Hence, you should use a simple inductance of a suitable value - depending on the desired oscillation frequency, of course.
(and you will have no problems finding a DC operating point).
Click to expand...

Hi!

RLC circuit work correct i think.
Howewer all circuit doesn't work correctly.
I add you some waveforms.

 

Re: Colpitts Generator Pspice

LvW said:
What does this mean???
Click to expand...

I'm sorry.

I meant that this circuit doesn't work like generator and i don't know why.
I ask you for help.
 

Re: Colpitts Generator Pspice

arek462 said:
I'm sorry.

I meant that this circuit doesn't work like generator and i don't know why.
I ask you for help.
Click to expand...

Did you follow my recommendation in post#6? (Inductor only).
What is the desired frequency?
Do you know the formula for the oscillation frequency?
 

Re: Colpitts Generator Pspice

LvW said:
Did you follow my recommendation in post#6? (Inductor only).
What is the desired frequency?
Do you know the formula for the oscillation frequency?
Click to expand...

You are genius. It was so simple.

I put coil instead rlc curcuit and it works well.

So now how can compute values of elements to get f=100k?
 

Re: Colpitts Generator Pspice

arek462 said:
So now how can compute values of elements to get f=100k?
Click to expand...
Horowitz's book does not say anything about frequency? They just drop the circuit there without saying anything?
 

Re: Colpitts Generator Pspice

arek462 said:
You are genius.
Click to expand...

Yes - I know.
But seriously: The "secret" is that I know the working principle behind the Colpitt oscillator - that`s all.
 

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