Hello,from page 486 of art of electronics book there is this example I am trying to understand how to optimize the noise of such system.
The transistordatasheet is presented below.photos and full pdf is attached.
In the book they dont describe exactly the inpus source.
Few questions:
1.what source to use in the LTspice simulation?
2.Is there a way to recreate the shot and johnson noise in a table in ltspice as shown below?
Thanks

https://www.onsemi.com/pdf/datasheet/mmbt5089-d.pdf

 

hi yef,
Check out this AAC article, for Noise simulations.
E
https://www.allaboutcircuits.com/technical-articles/Noise-Analysis-Using-LTspice-Tutorial/


Added @yef smith
https://www.analog.com/en/resources/media-center/videos/5579265856001.html

 

hi yef,
This is the sim for your posted circuit.
Used a different transistor.
E

 

Hello Eric,few questions:
1.How do you define noise source 7 nv/sqrt(Hz) as they say in the book.
2. given the circuit how did you know to choose the following source input?

 

hi yef,
Have you watched and understood the LTSpice noise simulation video in that Analog link I posted?
E

https://www.analog.com/en/resources...ries/ltspice-ac-noise-analysis-tutorial.html#

 

Hello Eric, yes its the third video.
In the book example they define "few nv/sqrt(Hz)" noise from the input.
in the example video they dont mention this.
how do I definesource input noise?
Thanks.

 

hi yef,
I do it by adding series resistance to the Vinput source.Try changing Rser.
Note: I do not have the model for the Book transistor.
E

 

Hello ,two questions:
1. a resistor is creating johnson noise which is stable threw the BW.
1.29×10−9V/sqrt(Hz) as shown in the calculation.
why the plot is not stable threw out the all frequencies?
2.given this simple example how do I do Noise figure in ltspice?
Thanks.

 

hi yef,
These are the LTSpice noise limitations as explained in the Help files.
E

 

Hello Eric,given the 100ohm resistor creating input noise Is there a way to calculate noise figure in LTspice from the simulation of the circuit ?
Thanks.

 

hi yef.
This is one method for SNR , ref link
Post your calculations.
E
https://www.google.com/search?client=firefox-b-d&q=ltspice+signal+to+noise+ratio

 

hi @yef smith
Is this LTSpice sim method helpful?
Unzip the file into same folder.
E

 

Noise Figure [in dB]:

NF = 10 log (Vn² / 4kTRs)

You get Vn², the total input noise power, contributed by the source resistance Rs and the DUT, from the noise simulation (inoise in V²/Hz). 4kTRs is the input noise power due to the source resistance Rs.
I don't know if LTspice can plot the whole formula and give you directly NF as a function of frequency.

 

Also see example educational file NoiseFigure.asc.