Noise Source and Noise Measurement Basics

Gregory covers the essentials of Noise Sources and Measurements, focusing on the use of a BJT transistor as a noise source. The BJT is configured with a reversed bias at its base-emitter junction, followed by a series of common-emitter amplifiers.

To analyze the noise at the circuit output, Gregory employs a Spectrum Analyzer with a noise marker function. This data is then used to estimate the BJT Excess Noise Ratio (ENR), factoring in the noise floor and amplification gain slope of the measurement setup.

The results are presented as Noise Power Densities and Noise Temperatures, chosen for their convenience in respective calculations. This approach allows for a straightforward yet thorough exploration of the noise characteristics.

BJT PN Junction Noise Source

Video about Noise Temperature and SNR

This video was made possible by Patreon support:

00:42 - Circuit overview
01:32 - Motivation for the measurements
02:54 - Noise characteristics
04:14 - Noise Power Density
05:48 - Reverse-biased base-emitter junction
06:46 - Spectrum analyzer measurement
08:08 - RBW and noise marker
11:24 - Automated measurements
14:54 - Amplifier gain de-embedding
17:10 - Excess noise ratio ENR
19:00 - Spectrum analyzer noise floor correction
23:04 - Circuit description
26:04 - Noise from Zener effect and Avalanche Breakdown

[DoniSouzazs]

The practical use of this circuit is to synthesize the sound of a chinbal from an electronic drum from the 70s. very good video.. merry Christmas
​🤣🪘🪘

[juanalfaro]

Thanks for your videos, I don't speak English but I watch your videos with subtitles :)

[andersonnobre]

Thank you Eng. Greg! I had learned a lot with you video !!! I am Brazilian Electronic.

[arashghasemi]

User should be careful to ALWAYS put a bandpass filter between the noise source outpur and the spectrum analyzer inout to prevent overloading the input power . Usually between 10dbm 20dbm is safe however without bandpass filter, the noisegen will send that power over a wide range of frequency which according to parseval theorem, the totatl power will increase with an rms behaviour which can easily exceed 20 dbm

[bsuryasaradhi]

Nice one, I made a noise source recently using a R2M avalanche diode with a boost converter, the noise is definitely better, I used 2n5484 jfets in cascode configurations for a 100mhz flat bandwidth, Love your videos man.

<3 from India.

[ConradoBelmonte]

Hello my friend! I really appreciate your YouTube Channel, your content is amazing! I'm learning a lot!

[jluke]

Great Video and Great Explanation. Thank you.

[InssiAjaton]

If you look certain transistor noise curves by the manufacturers (generally provided only for LOW NPOISE parts) you probably notice that they present the graphs on a logarithmic frequency scale (x-axis). You show a linear scale. which changes the apparent curve shape. If I recall, the ‘815 spectrum analyzer can produce its result on logarithmic, as well as linear scale.
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Another little note is that your supply voltage is rather low for approximating constant current. If the voltage would be raised to, say 24 V, you would be considerably closer to constant current feed (on a 5 V reverse bias junction. By the way, if you would use ordinary diodes, they generally have much higher reverse voltages and operate in Avalanche mode, rather than in transition between zener and avalanche. But there is a change in both noise amplitude and noise spectrum - the first one becoming higher, while the spectrum gets narrower.
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Finally, if you would limit the issue of noise to audio range (<20 kHz) you would need to consider the polarity symmetry. Possibly you would need two noise generating junctions, one fed from positive supply and the other one from negative one, and then the two noise signals summed into the output amplifier stage. And you would need to choose between white and pink noise. All that is beyond your scope in this presentation, but maybe something you may touch some time in the future…

[carlosrpdsj]

Hey Gregory, excelent video. Congratulations. I need your help! You've talked about a "blow filter" in a old video. Where can I found that content?

[GregStrike]

Digging the channel Gregory. Especially enjoyed the PLL!

[ArcFlashWarning]

Gregory, excellent content. Thank you.
Question, your prototype board traces almost look like some kind of copper tape. Do you etch them or do u have some type of sticky copper trace?

[lkossbu]

Very interesting and well explained as a professor!! I would ask you the behaviour of the two stages following the noise source: I can see a higher gain at low frequencies and a lower gain at higher frequencies as expected (due to Ft of every BJT)but these devices can add their noise (F) which is 1/f noise as well! Now, how much of 1/f noise is included in the "1/f" gain curve/noise output of the stages?
Thanks,
Andrea

[profdc]

BAT17 schottky diode can also serve as a good noise diode source too. Also a UHF transistor like 2SC3356 or BFR92 works ok too.

[Donquixote-qvsp]

Great video. I have a question. How to measure the Noise Figure of a Mixer? any guidance? Thanks.

[taucomini]

Nice video! A quick question: why are you using the markers to read out the spectrum? Should it not be much quicker to read out the power spectrum and normalize it to power density by hand afterward? Am I missing something?

[ruisacramento]

Suggestion to present in one video: Increase the temperature and observe the power generated using the formula N=kBT (where k is the Boltzmann constant, and B*T represents Bandwidth * Temperature).
And try predict bandwidth urs noise source that u made it. by : B=N/(k*T)

[projectrubick]

Hi, my friend. Do you still have the hotmart courses for sale?

[rogeronslow]

Hello Greg. Nice video.
What make of component drawers do you have? I see the little drawers are made of clear plastic which seem impossible to get these days.

[michaelbulley]

8:49 nice explanations l. Would love to learn where you found those clear (and wide) parts drawers!

[ernestb.]

Very interesting topic to study and to play with. One thing I was asking myself. The noise source and noise of the spectrum analyzer add, but not in a arithmetic way, but rather like square root of quadratic summation that is used for adding up random sources of error? So the part you 'just' subtract the noise floor would also not be completely right. But maybe I am 'splitting hairs' here 😀and is your approach probably usable. Again, interesting video 👍