Hello.
I'm intending to work with some oscillators but I have never actually worked with them before and I have some pretty basic questions about them.


I'm trying to understand these two circuits.
A driscol

And a colpitt

My knowledge of oscillators is just about 0 and I can't find any simplistic guides that will lead me to understanding these circuits.
I learn extremely fast with straightforward explanations rather than complex theory.
I would be very appreciative if someone could give me a step by step explanation into the workings of these two circuits.

What I have been able to gather is that the Q factor of a crystal is how well it maintains its frequency and the drisol circuit provides a low impedance to the crystal which gives it a higher Q factor.
It seems that L2 biases the transistor while providing a high impedance against the crystal so the transistor can act as a transimpedance amplifier.
D1 and D2 appear to be a Vswing limiter but as far as the feedback portion of the circuit I have no idea what is going on.
For the colpitt it seems to be feeding back the crystals frequency at emitter by the ratio of C1 and C2.
But I'm struggling to understand what this helps exactly.
Also it if putting a low impedance across the crystal provides a great Q factor than isn't the colpitt worse? Or does the feedback capacitors do this somehow?
Thanks.

 

I think that the Driscol is using the crystal in series resonant mode while the Colpitts is using parallel resonant mode hence the different impedances.

 

But I don't understand what that means.
I'm hoping for a "for dummies" explanation of the circuits.
I have never dealt with resonant circuits before.
I don't even know if the crystals oscillate on their own or if the freedback portion of the circuits are required for oscillation.

 

But I don't understand what that means.
I'm hoping for a "for dummies" explanation of the circuits.
I have never dealt with resonant circuits before.
I don't even know if the crystals oscillate on their own or if the freedback portion of the circuits are required for oscillation.

There is no spoon. There is not a "for dummies" explanation. You need to understand the basics before understanding somewhat complex circuits.

 

Basics of what exactly? I need directions.

 

I don't even know if the crystals oscillate on their own or if the freedback portion of the circuits are required for oscillation.

The crystal is like a fancy tuned circuit and needs amplification and feedback to make an oscillator.
See https://hackaday.com/2017/01/17/understanding-the-quartz-crystal-resonator/

 

Basics of what exactly? I need directions.

https://courses.e-ce.uth.gr/CE433/tutorials/VCO.pdf
https://www.allaboutcircuits.com/textbook/

 

Hello.
I'm intending to work with some oscillators but I have never actually worked with them before and I have some pretty basic questions about them.


I'm trying to understand these two circuits.
A driscol

And a colpitt

My knowledge of oscillators is just about 0 and I can't find any simplistic guides that will lead me to understanding these circuits.
I learn extremely fast with straightforward explanations rather than complex theory.
I would be very appreciative if someone could give me a step by step explanation into the workings of these two circuits.

What I have been able to gather is that the Q factor of a crystal is how well it maintains its frequency and the drisol circuit provides a low impedance to the crystal which gives it a higher Q factor.
It seems that L2 biases the transistor while providing a high impedance against the crystal so the transistor can act as a transimpedance amplifier.
D1 and D2 appear to be a Vswing limiter but as far as the feedback portion of the circuit I have no idea what is going on.
For the colpitt it seems to be feeding back the crystals frequency at emitter by the ratio of C1 and C2.
But I'm struggling to understand what this helps exactly.
Also it if putting a low impedance across the crystal provides a great Q factor than isn't the colpitt worse? Or does the feedback capacitors do this somehow?
Thanks.

Have you ever heard of LTSpice? Lots of people here use it, and some are quite the experts. I suggest you download it and start playing with it. Many of the basic concepts will become clear to you as you sim more complex circuits, until you start to see the "light" governing general analog electronics. I speak from personal experience.

 

Are you specifically interested in crystal oscillators? If not, there are other oscillators that are easier to understand.

Bob

 

Without knowing your intended use for such a circuit(s) it is difficult to explain anything, really.

Oscillator Basics
Oscillator Basics II
Electronic Components: Oscillators
Oscillators: Crystal
Another Link
Yet Another Link

Thank You Google!
I don't use it as often as I should either...

 

Are you specifically interested in crystal oscillators? If not, there are other oscillators that are easier to understand.

Bob

Yeah, actually I have a very specific interest in the two circuits I posted in particular because I want to build and refine them for a project.

I think I'm beginning to understand now.
In the equivalent tank circuit of a crystal the inductor draws current into the capacitor and when the cap is charged the inductor inverts the current and discharges the cap at which point it inverts again and charges the cap, etc.
The resonant frequency is where the impedance is lowest so this is where the oscillation happens.
So in order to keep the process going a positive feedback is required to keep the circuit energized?
I would think a simple resistor would do that though? I think I missed something.

I was looking at the pierce oscillator and the feedback at each end of the crystal is 180 out of phase which would make the feedback negative but the description said it was positive? I don't understand.

In the driscol example it seems that the transimpedance circuit is feeding the base of the transistor with an in phase feedback signal through bandpass filter of around 30MHZ-96MHZ. I'm guessing this is to eliminate the fundamental and activate the crystals overtone frequency?

 

I think I'm beginning to understand now.
...
I would think a simple resistor would do that though? I think I missed something.

See, that was easy.

It can't be a simple resistor, you need a 'negative' resistance function.
https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part5/page1.html

 

How does the gain of the feedback affect the oscillator Q?

 

Hello,

One of the parts that shows a negative resistance is a tunnel diode.
Google images already shows a lot of circuits with it:
Tunnel diode oscillator

Bertus

 

DIY tunnel diode?
http://www.sparkbangbuzz.com/els/ntype-nr-el.htm

 

Anyone know the answer to my above question?
Also I'm attempting to recreate the driscol circuit above in spice but I cannot manage to get it going.
What am I doing wrong?

 

Anyone know the answer to my above question?
Also I'm attempting to recreate the driscol circuit above in spice but I cannot manage to get it going.
What am I doing wrong?

It would also help if you included an image in your post. Some of us are browsing through this site using our phones.

 

Sorry, updated with pic.

 

You replaced a BJT with a FET.

 

Whoops yeah. Putting a BJT in does not make it work though.