Yes their jig creates a noise-free base current even though the jig itself is powered from an ordinary benchtop variable power supply, and even though it uses conventional metal film resistors operating at 300K (not at absolute zero).
I don't see how forced base current biasing is useful in this situation. Forcing collector current works fine the correlation is weak. I haven't seen anyone declare that there is some horrible inaccuracy in measuring the current noise of an op-amp by making a follower with gain and simply putting a big resistor in series with the non-inverting input.
Yup, AOE uses a combination of precision resistors, feedback loop, and trimmer pots, to set VCE=constant1 with ICE=constant2. IBE is whatever it needs to be, to give the required ICE. They take pains to eliminate sources of noise other than the DUT itself. (DUT operates at room temperature).
Cooling is a whole lot of hassle for not much omprovement. If you arent doing IR maps of the cosmos there are easier ways to low noise. Quantech used trasformers on the resistor analyzer. Useful down to less than 10 Ohms.
I can supply the schematics for both the older and last gen semi noise analyzers. No magic. Good engineering and understanding of the problems.
A new generation of the transistor fixture using modern parts would be nice. Its complicated with several floating supplies and bias options.
Sent from my LG-H811 using Tapatalk
I can supply the schematics for both the older and last gen semi noise analyzers. No magic. Good engineering and understanding of the problems.
A new generation of the transistor fixture using modern parts would be nice. Its complicated with several floating supplies and bias options.
Sent from my LG-H811 using Tapatalk
Generally speaking, yes, a Peltier can get you down that far. As far as their necessity, I've only used them on EMCCD cameras, where we were down towards photon counting levels. The thermal noise reduction was absolutely necessary there, but it'd be awfully difficult to justify for *anything* audio.
Bipolars (silicon) don't work at 77K. For the most part only exotics work at cryo temperatures some even at 4K.
Aaaaahhhh! What the heck do they use on Mars for the Rover?
Did i mention the jesuit scholastic who got a kick of putting an oscar meyer wiener in the nitrogen flask, then hitting it with a mallet getting pork detritus all over the solid state lab?
Old paper and don't know what the state of the art is anymore, (but band gaps haven't changed!) but this ORNL report suggests that even minority carrier devices made on silicon were getting okay results at LN temps. SiGe and III-V class materials dominate this market though.
https://digital.library.unt.edu/ark:/67531/metadc672147/m2/1/high_res_d/231535.pdf
https://digital.library.unt.edu/ark:/67531/metadc672147/m2/1/high_res_d/231535.pdf
True.
I couldn't remember if LN freeze-out was severe enough in Si to completely preclude minority carrier devices (i.e. thinking totally academically, not practically). Anyhow, I'll stop this sidebar, as it doesn't help further the cause of this thread. Cryogenic semiconductors are important in a number of fields, but except for a few folks' non-DiyAudio contributions, outside the scope of this forum.
I couldn't remember if LN freeze-out was severe enough in Si to completely preclude minority carrier devices (i.e. thinking totally academically, not practically). Anyhow, I'll stop this sidebar, as it doesn't help further the cause of this thread. Cryogenic semiconductors are important in a number of fields, but except for a few folks' non-DiyAudio contributions, outside the scope of this forum.
It seems one can evade to SiGe BJTs.
< http://authors.library.caltech.edu/9341/1/WEIieeemtt07.pdf >
< https://hal.inria.fr/file/index/docid/253110/filename/ajp-jp4199404C616.pdf >
< Extreme-Temperature Electronics (Tutorial - Part 3) >
They are not exotic any more.
< https://www.infineon.com/cms/de/pro...html?channel=db3a30432b16d655012b1e9ec92d5b2d >
BFP640 behaves like a normal BJT, we have used them in masses.
Just a bit sqirrely, and their Early voltage is close to infinity. 🙂
Infineon bragged about extra low 1/f corners, but that was in microwave
context, nothing that would impress us here.
< http://authors.library.caltech.edu/9341/1/WEIieeemtt07.pdf >
< https://hal.inria.fr/file/index/docid/253110/filename/ajp-jp4199404C616.pdf >
< Extreme-Temperature Electronics (Tutorial - Part 3) >
They are not exotic any more.
< https://www.infineon.com/cms/de/pro...html?channel=db3a30432b16d655012b1e9ec92d5b2d >
BFP640 behaves like a normal BJT, we have used them in masses.
Just a bit sqirrely, and their Early voltage is close to infinity. 🙂
Infineon bragged about extra low 1/f corners, but that was in microwave
context, nothing that would impress us here.
Referring back to AoE3 Fog. 8.92.
What is actually S1, a switch for discharging the large caps?
Patrick
What is actually S1, a switch for discharging the large caps?
Patrick
Yes. There is a current limiting resistor in front of the switch which prevents
frying the contacts. There is no such resistor in series to the wiper of R8.
Turning it fast ccw to the end might kill it. (0.35F, charged, as told in the foot note.)
frying the contacts. There is no such resistor in series to the wiper of R8.
Turning it fast ccw to the end might kill it. (0.35F, charged, as told in the foot note.)
Shouldn't R5 be connected to the top of Rc (at 12.5V) and not at the bottom (2.5V) ?
I mean you only want to measure the noise in Ic, correct ?
One can still create a separate 2.5V for biasing Q2 using a potential divider directly from the 12.5V, e.g. 200k/50k.
Patrick
I mean you only want to measure the noise in Ic, correct ?
One can still create a separate 2.5V for biasing Q2 using a potential divider directly from the 12.5V, e.g. 200k/50k.
Patrick
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I think the bottom end is right. That's the sense point of
the loop that controls VCE of the DUT. The bias of Q2
is not a fixed 2V5.
I'm not sure if I got all the details, it reminds me
somewhat at the Infineon BCR400W bias contoller.
the loop that controls VCE of the DUT. The bias of Q2
is not a fixed 2V5.
I'm not sure if I got all the details, it reminds me
somewhat at the Infineon BCR400W bias contoller.