Reverse engineering masks is easy.
Replicating the original wafer purity and diffusion and processing steps is hard
Hi all.
I am new here so excuse me if I am inadvertently violating some forum "etiquette".
I write here because I also bought a bunch of inexpensive chinese cloned 2SC2240, just to see how they measure, and to my surprise I also found out they were exceptionally good noise-wise, even slightly better than a known-good 2SC3324 (Toshiba SMT part, apparently the only low-noise transistor option left as of 2020).
I will share may test circuit and results if I find the time and if people show some interest.
However I wanted to comment on the test circuit from Regenpack. If I read well the source resistance at the base of the transistor is in the order of 20 Kohm, so at 100uA bias you will mostly be measuring the resistor noise, not the transistor contribution (unless you have a very lousy transistor with poor gain and terrible flicker noise, which can happen)
Low noise transistors are characterized by having a very low value of base spreading resistance (rbb). For a "good" 2SC2440 it should be somewhere between 30 and 50 ohm, which helps keeping noise down with very low source impedances (e.g. MC cartridges, microphones etc) at sufficiently high bias currents (say 1 to 4mA, where collector shot noise is no longer dominant). Now if you measure noise with a 20k ohm source impedance at 100uA bias you will never be able to find out if the transistor clone is really low noise or not.
But if your application indeed foresees such conditions, then your best bet would be a high gain low current device like 2N5088 or BC550C. Such transistors have rbb in the 500ohm - 1kohm range (i.e. they are not properly "low noise" devices) but if your source impedance is 20k then it doesn't matter. Just check that flicker noise corner is low enough to not degrade the source noise further at the bottom of the spectrum
Hope it helps
I am new here so excuse me if I am inadvertently violating some forum "etiquette".
I write here because I also bought a bunch of inexpensive chinese cloned 2SC2240, just to see how they measure, and to my surprise I also found out they were exceptionally good noise-wise, even slightly better than a known-good 2SC3324 (Toshiba SMT part, apparently the only low-noise transistor option left as of 2020).
I will share may test circuit and results if I find the time and if people show some interest.
However I wanted to comment on the test circuit from Regenpack. If I read well the source resistance at the base of the transistor is in the order of 20 Kohm, so at 100uA bias you will mostly be measuring the resistor noise, not the transistor contribution (unless you have a very lousy transistor with poor gain and terrible flicker noise, which can happen)
Low noise transistors are characterized by having a very low value of base spreading resistance (rbb). For a "good" 2SC2440 it should be somewhere between 30 and 50 ohm, which helps keeping noise down with very low source impedances (e.g. MC cartridges, microphones etc) at sufficiently high bias currents (say 1 to 4mA, where collector shot noise is no longer dominant). Now if you measure noise with a 20k ohm source impedance at 100uA bias you will never be able to find out if the transistor clone is really low noise or not.
But if your application indeed foresees such conditions, then your best bet would be a high gain low current device like 2N5088 or BC550C. Such transistors have rbb in the 500ohm - 1kohm range (i.e. they are not properly "low noise" devices) but if your source impedance is 20k then it doesn't matter. Just check that flicker noise corner is low enough to not degrade the source noise further at the bottom of the spectrum
Hope it helps
What about this? Is this a legit company attempting to produce generics of out of production part numbers?
Foshan Blue Rocket Elec|Foshan Blue Rocket Elec 2SA970|Transistors (NPN/PNP)|LCSC
The data sheet (page 3) has noise figure graphs:
https://datasheet.lcsc.com/szlcsc/1811141244_Foshan-Blue-Rocket-Elec-2SA970_C328605.pdf
Foshan Blue Rocket Elec|Foshan Blue Rocket Elec 2SA970|Transistors (NPN/PNP)|LCSC
The data sheet (page 3) has noise figure graphs:
https://datasheet.lcsc.com/szlcsc/1811141244_Foshan-Blue-Rocket-Elec-2SA970_C328605.pdf
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