barkhausen criterion using LTSPICE

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cmrincon

Joined Oct 25, 2017
40
Hi, probably LTspice is not the best software for doing this type of simulations but, is simpler than other software.

I want to graphically see the gain and phase of my oscillator in order to check frequency of the oscillations and gain, i like to archive something like loop-gain method where you can see where the phase is 0 and gain is 1 to see the conditions of the oscillator. Probably later i want to change values of resistances and the resonator values, in order to see how this parameters change the gain and the frequency of my oscillator.

Here you can find the oscillator already working, but without archive my purpose.

Greetings.
 

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Alec_t

Joined Sep 17, 2013
10,913
Could you use .MEASURE commands to read the parameters of interest, then view the results in the Error log?
 

ronsimpson

Joined Oct 7, 2019
450
Is this what your are looking for?
1581085938076.png

What changed.
V2 drives in to the base of Q1 with near zero impedance. It forces so much power into the LC that the LC can not work. Change the impedance of V2 to 50 ohms. Rser=50 Now the LC can short out V2 at resonant frequency.

V2 drives DC directly into Base of A1 forcing the Base voltage to 0V. Add C4 so R1 & R3 set the base dc voltage.

I changed R2 for a test. Graph is of Q1-Emitter. With R2=R4 q1-Collector has almost the same plot.

Also changed plot from 10 points to 100 points and could be set to 1000 points.
Have fun. Ron S.
 

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crutschow

Joined Mar 14, 2008
24,376
If you connect the V2 source like this with zero series impedance, it then has no effect on the oscillation frequency.
I added R5 control the loop gain.
The response at the emitter is shown.

1581094007527.png
 

Bordodynov

Joined May 20, 2015
2,501
You'll never get the result you want.
The low signal frequency will not match the real one. The transistor is a highly non-linear element. And its real steepness will be greatly reduced. To simulate this, I've added a tricky resistor with two values to the transistor emitter. Since I don't know the average steepness of the transistor, I've set a certain value for the resistors. You can see how the impedance changes at point Z. A phase of 180 degrees means negative resistance.
You must use a current generator. You can see approximately what the oscillation frequency is.

AB_AC.pngAB_tran.png
 

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