It's not "official permission". Farnell in the Netherlands won't take orders from anyone who isn't registered as a business with the local chamber of commerce. It's one of the ways that Dutch wholesalers distinguish themselves from retailers.
The minimum order isn't all that big - about 25 euro's when I last looked - and it discourages orders to small to cover the adminstartive costs of putting them together and sending them out.
I don't think than any constituency is being "pandered too". This is the way Dutch traders behave. They have been evolving this kind of behaviour for hundreds of years - since before there was a Dutch Republic - and it seems to work for them.
Your first supplier - your source of cheap BC577's - doesn't have any broadband transistors.
The second has BFR91 and BFR96 parts in the old pill-box package, which is easier to work with than the SMD-packaged BFR92 or BFT92. Tomorrow I'll see what I can get them to send me.
Not the way I see it; the advantage is that avalanche IS GAIN applied to the shot noise. That gain makes the signal big enough to dominate any additions in later amplifiers. Without that gain in the avalanche process, your later amplifiers are equal and hard-to-characterize additional sources of noise.
If you've got shot noise on a current, you need to have it develop about 50mV across your load resistor (at room temperature) to equal the Johnson noise in the load resistor. As you increase the resistance further, the voltage noise generated from the shot noise rises in direct proportion to the resistance, while the Johnson noise rises as the square root of the resistance.
It not that difficult to organise your circuit so that the shot noise is dominant, and also swamps the Johnson noise in the input stage of you first amplifier.
You are being obtuse, it is a decision made entirelyu by the company (Farnell) not to sell to private individuals. That's not official permission, it is their freedom of choice to choose this marketing strategy. Stupid though it may seem. I suppose the government could make laws dictating which entities companies must deal with, is that how it works in the USA?
You just need to know someone in a small company who would be willing to order a few parts for you, or work in one. Or have your own of course.
I can order from Farnell (a UK company) with no minimum order charge and free shipping. They regularly send me single items worth far less than UPS must charge them. Of course they make it back on the larger orders.
Simply imagining shot noise with gain can't and doesn't work. Consider a current of 10uA, that's 6.25M electrons per 10ns, and the random shot-noise variation would be 2500 in 10ns, or 0.04% noise.
Now imagine that each electron is multiplied by 100. Oops, that can't be right, because now we'd have 625M electrons per 10ns. OK, so scale back to 62500 electrons per 10ns, and let each of those turn into 100 by avalanche gain. Now the random "shot" noise would be 250 "events" per 10ns, or 0.4%.
But in reality the discrepancy is worse than that, much worse. We've learned that in avalanche, each starting electron actually starts a "microplasma" channel that conducts a channel current e.g., 20uA, lasting say 3 to 50ns, and ending abruptly, in under a ns, as the small nearby capacitance gets discharged and the local voltage no longer supports avalanche.
Some plasma channel electron-atom collisions emit photons, some of which create photoelectrons starting more channels nearby. It's all highly chaotic.
So we end up with an intermittent noisy "oscillation" of current pulses of quasi-random length. When you look at the waveform at longer timescales you see the superposition of thousands of events, which simply looks noisy. But with the right lashup and equipment you can view individual channels starting and stopping, sometimes on top of each other.
This topic, with ASCII waveforms, bench circuit-setup details, theory and literature references, was extensively covered here on s.e.d. many years ago. You can read all about it.
The government isn't involved at all. The local chamber of commerce registers businesses as a convenience to other businesses. As far as I know, registration - on its own - doesn't have any legal significance. If you want to get serious, or turn over more than a few thousand euro's of business in a year, you register yourself as business with the tax authorities. You then have to collect value-added-tax (VAT in English, BTW in Dutch) on your sales, subtract the VAT you have to pay on the stuff you buy and turn over the difference to the tax authoritees. Hiring people raises the ante again, but I've not bothered to get into that.
Says someone who designs electronics in the USA. I've not had much reason to suppose that US electronics is better than anybody else's. and in at least two areas I know well - electron microscopes and electron beam microfabricators - the US machines were less than impressive.
Yes! The old discussion was very nice. I liked the article by K.G. McKay "Avalanche Breakdown in Silicon" Phys. Rev. (94) pg 877. (May
15, 1954) It would be fun to see these different channels start to conduct as the voltage is raised. There are some temperature effects which also sound interesting.
(Wouldn't it be nice if these old articles were now part of the public domain?)
I'm a big fan of shot noise for this. By my actual measurement it's Gaussian out beyond 7.1 sigma, corresponding to a threshold crossing rate of 10**-11 times the bandwidth. Another key virtue is that the noise PSD is derivable from the DC photocurrent by a trivial first-principles calculation.
You do need a decent amplifier, and enough photocurrent to drop a volt or two across your (metal film) sense resistor, but it's easy to get way within 1 dB accuracy that way. Best of all, at least for electrooptics folk like yours truly, the frequency response is *exactly* that of your front end.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net
A lot of 1/f noise is actually popcorn in character. With peace to AD, it's getting worse rather than better as devices shrink--it's mostly local conductance fluctuations.
Electromigration is another source of popcorn noise.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net
I remember back in the day when you needed at least a business *name*, not necessarily some bureaucratic registration , to order parts from distributors in Canada--there was some regulation connected with sales tax IIRC.
My late friend Brian Murray, a really amazing tech who taught me how to tune fancy filters when I was but a stripling, called his imaginary firm "EnemaTronics", and nobody blinked an eye. (Subtlety was never Brian's thing--he came to my wedding in leathers. RIP.)
Cheers
Phil Hobbs
(Coming to you from the very pleasant Delta Sky Club in Salt Lake City, on my way to Albuquerque NM.)
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net
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