10 Mhz Colpitts Crystal Oscillator

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ahmann

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Hello guys! I am new to this forum and new to RF circuit design.
I am trying to design 10 Mhz Colpitts Crystal Oscillator with BJT.
My input is 5V DC and my output will be 10mW sinusoidal on 50 ohm.
I found a design from previous years and have been working on it, however, since I am not familiar with which component does which job, i cannot go any further. I am in desperate need of help to understand the circuit and meet the requirements.
Spesifically I need to find out how to determine component values. Is there a formula or are we just trying random values on Spice?
Any kind of help is appreciated. Thanks in advance!
 

**broken link removed**
 

With all due respect but I think the link you posted is not about crystal colpitts.
 

Yup that is true the one is for basic colpitt's design trial and error is worth without knowing the crystal name and more of its props

- - - Updated - - -

Do post them for more info
 

ahmann said:
With all due respect but I think the link you posted is not about crystal colpitts.
Click to expand...

nor is yours !!

so what research have you done to locate examples of crystal controlled Colpitts oscillators ?
we are not just going to spoonfeed you the answers, find some examples and if you have specific questions relating to those circuits
then ask us

Dave
 

Ok Dave I will be more specific. The part until the just after first transistor is basic colpitts. So i just put necessary components to pre-specified places. However i dont know how to choose bias resistor and capacitor values. The second part is nothing but a buffer to isolate circuit from loading. L2-C8 and C9 forms tank circuit for better frequency selection. I dont know how to choose bias resistors and the values capacitor- inductor as well. Thanks
 

What you have shown is a fundamental, parallel mode Colpitt oscillator. With the net parallel load capacitance on the crystal it should be selected for about 10 pF load capacitance.

The pick off for the second stage is well isolated to prevent too much impact to frequency stabiltiy due to second stage loading. It is a trade off on how much power is delivered to second stage.

There are many references on web for crystal Colpitt osc design.

one such, https://ww1.microchip.com/downloads/en/appnotes/00826a.pdf
 

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