Hi, can somebody help to explain feedback transistor please

Thread Starter

michael1978

Joined Jun 29, 2014
309
Hello to everbody,

can somebody expain how work and what they form feedback capacitor inductor resistor,
if it was only resistor feedback i understand, but this make me dificult to understand with capacator and inductor....
and also L2...thnx.
FEEDBACKANALYSIS.png
 

Thread Starter

michael1978

Joined Jun 29, 2014
309

Ylli

Joined Nov 13, 2015
799
What is the transistor type, and what is the application? Is this an RF Power output stage? The RLC base to collector can sometimes be used to 'neutralize' the transistors base - collector capacitance. A link to the origin of this circuit would be helpful.
 

DickCappels

Joined Aug 21, 2008
5,950
It looks a lot like a notch filter with a limited depth. This circuit is rare and probably designed to solve a particular and unusual requirement.
 

Thread Starter

michael1978

Joined Jun 29, 2014
309
Hello,
This circuits is for rf design, and i build in multisim, with ac voltage of 1v peak, but i dont see any change in circuit i measure voltage and current is the same when i change the frequency
 

Thread Starter

michael1978

Joined Jun 29, 2014
309
What is the transistor type, and what is the application? Is this an RF Power output stage? The RLC base to collector can sometimes be used to 'neutralize' the transistors base - collector capacitance. A link to the origin of this circuit would be helpful.
Hi, yes is for rf design, but i dont see so much changes when i change the frequency
 

Ylli

Joined Nov 13, 2015
799
Hi, yes is for rf design, but i dont see so much changes when i change the frequency
I sim'd it in LTSpice and I didn't see any variations in the passband or phase either. I think with that 1K resistor there isn't enough feedback to make any difference.

(I used a 15 volt source on the collector and used a 47k resistor from +15 to the base to bias the transistor - sim'd with a 2n3904)
 

crutschow

Joined Mar 14, 2008
23,542
Below is the LTspice simulation of the circuit similar to Ylli's version for 1Ω, 10Ω, 100Ω, and 1kΩ values of R1.
L1C1 has no discernable effect on the gain for R1=1kΩ (green trace), the original value, but shows increasing rolloff as R1 is reduced to 1Ω (yellow trace).

upload_2018-6-28_22-44-10.png
 

Thread Starter

michael1978

Joined Jun 29, 2014
309
I sim'd it in LTSpice and I didn't see any variations in the passband or phase either. I think with that 1K resistor there isn't enough feedback to make any difference.

(I used a 15 volt source on the collector and used a 47k resistor from +15 to the base to bias the transistor - sim'd with a 2n3904)
thnx man, but i dont understand, what they do LC Tank, you can use only one resistor for feedback, why also LC, is possible a lttle bit to explain me more in detail, i know they resononate at 11.25Mhz, but more i dont know, and also my circuits he dont have a Resistor 47k, do you want to send you my software,you understand more than me?
 
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Thread Starter

michael1978

Joined Jun 29, 2014
309
Below is the LTspice simulation of the circuit similar to Ylli's version for 1Ω, 10Ω, 100Ω, and 1kΩ values of R1.
L1C1 has no discernable effect on the gain for R1=1kΩ (green trace), the original value, but shows increasing rolloff as R1 is reduced to 1Ω (yellow trace).

View attachment 155284
Hello, but me i dont understand what they do lc, you can use only one resistor feedback, what for changes they do lc
 

ericgibbs

Joined Jan 29, 2010
8,886
hi michael,
Look at this link, note the response plot of that series L C circuit.
You see at resonance the series impedance is the lowest value, this means the negative feedback is at a maximum, so the circuit gain is at a minimum.

https://www.electronics-tutorials.ws/accircuits/series-resonance.html

Look at the Yellow line plot in post #11, shows the gain
Update: you recall that you calculated Fres ~ 11.25MHz, compare that with the Yellow plot.
E
EDIT:
Clip from that link.
AA1 29-Jun-18 09.59.gif
 
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Thread Starter

michael1978

Joined Jun 29, 2014
309
hi michael,
Look at this link, note the response plot of that series L C circuit.
You see at resonance the series impedance is the lowest value, this means the negative feedback is at a maximum, so the circuit gain is at a minimum.

https://www.electronics-tutorials.ws/accircuits/series-resonance.html

Look at the Yellow line plot in post #11, shows the gain
Update: you recall that you calculated Fres ~ 11.25MHz, compare that with the Yellow plot.
E
EDIT:
Clip from that link.
View attachment 155296
Thnx Man, i am reading this article….
 

Thread Starter

michael1978

Joined Jun 29, 2014
309
hi michael,
Look at this link, note the response plot of that series L C circuit.
You see at resonance the series impedance is the lowest value, this means the negative feedback is at a maximum, so the circuit gain is at a minimum.

https://www.electronics-tutorials.ws/accircuits/series-resonance.html

Look at the Yellow line plot in post #11, shows the gain
Update: you recall that you calculated Fres ~ 11.25MHz, compare that with the Yellow plot.
E
EDIT:
Clip from that link.
View attachment 155296
Hi, i read fast the article, at resonance frequency current is at maximum
hi michael,
Look at this link, note the response plot of that series L C circuit.
You see at resonance the series impedance is the lowest value, this means the negative feedback is at a maximum, so the circuit gain is at a minimum.

https://www.electronics-tutorials.ws/accircuits/series-resonance.html

Look at the Yellow line plot in post #11, shows the gain
Update: you recall that you calculated Fres ~ 11.25MHz, compare that with the Yellow plot.
E
EDIT:
Clip from that link.
View attachment 155296
Like i read fast at resonance frequency, the current is at maximum, of xl xc act like a short, only the resistance stay to calucalte, so it dependes how small of large the value of R is, and the current depends on R, I=V/R os is R small more current is R high low current RIGHT?
 

ericgibbs

Joined Jan 29, 2010
8,886
hi m,
In that circuit a 1k resistor is so large compared to the L and C impedances near resonance, it is 'dominant' so it masks out the effect of the LC.
As the R value is reduced, the LC impedances are effective to a greater degree.
Do you follow OK.?
E
 

Thread Starter

michael1978

Joined Jun 29, 2014
309
hi m,
In that circuit a 1k resistor is so large compared to the L and C impedances near resonance, it is 'dominant' so it masks out the effect of the LC.
As the R value is reduced, the LC impedances are effective to a greater degree.
Do you follow OK.?
E
I think i understand, like you say, "Look at the Yellow line plot in post #11, shows the gain", i see the result, of graph 1Ω, 10Ω, 100Ω, and 1kΩ values of R1.
yes i think i understand now, because i have special sofware, it tells everything about gain and impedance and losse, you just have o put one value for the rest he do, and i dont understand how it works, but now i understand so now is easy to do experments
Thnkx a lot ;)
 

Thread Starter

michael1978

Joined Jun 29, 2014
309
I think i understand, like you say, "Look at the Yellow line plot in post #11, shows the gain", i see the result, of graph 1Ω, 10Ω, 100Ω, and 1kΩ values of R1.
yes i think i understand now, because i have special sofware, it tells everything about gain and impedance and losse, you just have o put one value for the rest he do, and i dont understand how it works, but now i understand so now is easy to do experments
Thnkx a lot ;)
Ohh Man sorry i forget i did not get answer about L2 and R2, what does do L2 or what makes L2 and R2
 
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