RF Transistor Noise Source
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From: Phil Hobbs on 29 Dec 2009 20:42 On 12/29/2009 8:32 PM, RST Engineering wrote: > On Tue, 29 Dec 2009 16:57:23 -0500, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > > >>> >> >> Gotcha. My son Simon is going to make some dough by insulating the >> attic. I wanted to use vermiculite but you basically can't get it any >> more--which is a pity. You have to use a bit more, but you don't wind >> up with red eyes and itchy skin the way you do with rock wool or fibreglass. > >> Phil Hobbs >> >> "There is no bad weather, there are only wrong clothes." > > I thought kitty litter was almost pure vermiculite. > > Jim > Clay, usually. Vermiculite is a kind of mica that unfolds like an accordion when you heat it. It isn't like anything else. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: George Herold on 29 Dec 2009 20:51 John Larkin wrote: > On Tue, 29 Dec 2009 02:27:37 -0800 (PST), Wimpie <wimabctel(a)tetech.nl> > wrote: > > >On 29 dic, 09:56, Robert Baer <robertb...(a)localnet.com> wrote: > >> m...(a)sushi.com wrote: > >> > On Dec 28, 1:49 pm, RST Engineering <jwei...(a)gmail.com> wrote: > >> >> . > >> >> . > >> >> There was a general discussion in this NG a couple of weeks ago about > >> >> using a lightly-biased zener as a noise source. �There was no clear > >> >> definition about how flat or to what frequency the noise was useful.. > >> > >> >> It got me to thinking and I'll do the experiment as soon as I can > >> >> clean off my bench, but what do you think I'm going to see for > >> >> reasonable noise bandwidth if I use a small signal (like a 2N5770 or > >> >> 918) and use the emitter-base junction as the zener. �Most of them > >> >> zener somewhere around 5 volts and that should be reasonable. > >> > >> >> Most of the comments regarding bandwidth using a "regular" zener > >> >> centered around the rather large junction area necessary to carry some > >> >> decent current; the junction of an RF transistor ought to be at least > >> >> an order of magnitude (several??) smaller than that. > >> > >> >> Thoughts? > >> > >> >> Jim > >> > >> > One thing to keep in mind is the transistor is easily damaged when > >> > zenered. You should do this with a current limited supply, say 100ua.. > >> > >> > If you've ever done ESD testing or fuse testing, invariably the > >> > reverse biased diode is the thing that is easily fried. When popping > >> > metal fuses, you need to insure that the inductive kick of the zapper > >> > is such that after popping the fuse, the diode junction gets forward > >> > biased. This does dump current into the device, but that can be > >> > controlled by the size of the capacitor used in zapping. For ESD > >> > structures where there is no diode to the positive rail, the snap back > >> > of the "off" nfet saves the parasitic diode junction. > >> > >> � �Be advised that the damage to a zenered transistor E-B junction is a > >> time * current or dosage product, exactly as if it got radiation damage. > >> � �Total dosage: a little over a long time = = a lot over a short time. > >> � �Fairchild uA709s used in the Apollo got "nailed" by that. > >> � �Turns out the company hired to test and burn them in did not know > >> what an op amp was or how to test them or even burn them in despite a > >> burn-in circuit in the data sheet! > >> � �Their circuit zenered the inputs and that caused a failure mode > >> during a mission. > >> � �Fairchild engineers had to teach some basic electronics, and then > >> advance to op amps and test methods as part of proof the 709s were not > >> initially bad. > >> � �The other part was a setup burning in NIB same date lot code parts in > >> 2 batches: one using the nasty circuit and the other using the datasheet > >> circuit. > >> � �Oh yes; the cure is to anneal out the damage in an oven. > > > >Hello Robert, > > > >I did some experiments with low current reversed bias to the BE > >junction of BC847. Even at low reverse current (10uA for several > >hours), the HFE at low collector current (<10uA) drops significantly > >after applying the reverse current. > > > >It looks like adding a resistor parallel to the BE junction as the HFE > >at high current did not drop significantly. > > > >Does such dosage degradation to junctions also occur when reverse > >biasing microwave schottky mixer diodes, or PN junction diodes? > > > >Best regards, > > > >Wim > >PA3DJS > >www.tetech.nl > >please remove abc in case of PM. > > "Reference zeners" like the 1N935 sort of guys, are remarkably stable > over time. They are usually a stack of a zener in series with one or > two forward diodes, giving a TC that is zero at some current around > 7.5 mA, usually. You can tune the current to hit zero TC. > > http://www.microsemi.com/datasheets/SA6-7.PDF > > > The best way to get a really good current source is to use the > reference zener to make its own current source, using a simple > bootstrap circuit. Just make sure it starts up! > > I once bought a 6.2 volt zener from Motorola for $35, which was a lot > of money then. It came in a presentation-quality tube with a 1000-hour > graph of stability, signed by all sorts of important people. > > Some good stuff here: > > http://focus.ti.com/lit/an/slyt183/slyt183.pdf > > John > "Reference zeners" like the 1N935 sort of guys, are remarkably stable > over time. They are usually a stack of a zener in series with one or > two forward diodes, giving a TC that is zero at some current around > 7.5 mA, usually. You can tune the current to hit zero TC. Interesting thanks, Iâve used the LM399âs that come with a nice plastic cover and heater circuit. They run right about 6.95 Volts, which Iâve always thought was the âmagicâ balance point between âtunnelingâ zener current and âavalancheâ zener current, (but maybe thereâs another diode in series?). For a noise source I think the avalanche zeners above 7 V will be much better than tunneling zeners. I think (though Iâm half talking out of my a$$ since I havenât made the measurements.) that tunneling zeners should show about the same noise as forward biased diodes. (At least if you measure the current noise.) This assumes that the only noise source is shot noise. Say do zenered pnpâs show more noise than zenered npnâs? (Iâve never measured the zener voltage of a transistor.) George H.
From: George Herold on 29 Dec 2009 20:53 John Larkin wrote: > On Tue, 29 Dec 2009 00:43:19 -0800, Robert Baer > <robertbaer(a)localnet.com> wrote: > > >RST Engineering wrote: > >> . > >> . > >> There was a general discussion in this NG a couple of weeks ago about > >> using a lightly-biased zener as a noise source. There was no clear > >> definition about how flat or to what frequency the noise was useful. > >> > >> It got me to thinking and I'll do the experiment as soon as I can > >> clean off my bench, but what do you think I'm going to see for > >> reasonable noise bandwidth if I use a small signal (like a 2N5770 or > >> 918) and use the emitter-base junction as the zener. Most of them > >> zener somewhere around 5 volts and that should be reasonable. > >> > >> Most of the comments regarding bandwidth using a "regular" zener > >> centered around the rather large junction area necessary to carry some > >> decent current; the junction of an RF transistor ought to be at least > >> an order of magnitude (several??) smaller than that. > >> > >> Thoughts? > >> > >> Jim > > Well, all of the bipolar transistors seem to have the_specification_ > >of a max reverse VBE of 5 volts, but in fact they all zener in the 8 > >volt region. > > Lots of NPNs zener around 5 volts. If you use the collector and > emitter, you get a "reference zener", a zener in series with a > forware-biased diode, around 6.2 volts with a very low TC. > > For some reason, PNP transistors sometines have higher zener voltages, > 10-12 volts maybe. > > John Cool, do you do anything with the base? Seems a shame to just leave it hanging. George H.
From: krw on 29 Dec 2009 23:07 On Tue, 29 Dec 2009 17:51:36 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: >On Tue, 29 Dec 2009 17:46:24 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: > >>On Tue, 29 Dec 2009 15:12:25 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: >> >>>On Tue, 29 Dec 2009 16:57:23 -0500, Phil Hobbs >>><pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>>[snip] >>>> >>>>.... My son Simon is going to make some dough by insulating the >>>>attic. I wanted to use vermiculite but you basically can't get it any >>>>more--which is a pity. >> >>They make loose cellulose insulation. My (new) house has it, bit it's >>a PITA, IMO. It doesn't itch (been working in it this week), but >>*does* compress. >> >>>That IS a shame. Best insulated house I ever owned had vermiculite >>>filled walls. >>> >>>Only problem was if I cut a hole to add, for instance, another >>>electrical outlet... it poured out on the floor. >> >>That too. I still haven't replaced it in the wall above the sub-panel >>I put in. I'm finishing that room so the insulation won't be needed. >> >>>So I'd catch it in a bucket, do my wire pulling, put the box in place, >>>and seal it. Then go up in the attic and re-pour the vermiculite ;-) >> >>Umm, walls aren't supposed to be open at the top, for *many* reasons. > >Some of us are clever enough to pour it thru the wire hole ;-) > >(Vermiculite is about the size of rice.) > The insulation I've seen is more like popcorn or pea gravel. Even wire holes are supposed to be sealed, though I suppose it's less important on exterior walls.
From: Robert Baer on 30 Dec 2009 01:03
Wimpie wrote: > On 29 dic, 09:56, Robert Baer <robertb...(a)localnet.com> wrote: >> m...(a)sushi.com wrote: >>> On Dec 28, 1:49 pm, RST Engineering <jwei...(a)gmail.com> wrote: >>>> . >>>> . >>>> There was a general discussion in this NG a couple of weeks ago about >>>> using a lightly-biased zener as a noise source. There was no clear >>>> definition about how flat or to what frequency the noise was useful. >>>> It got me to thinking and I'll do the experiment as soon as I can >>>> clean off my bench, but what do you think I'm going to see for >>>> reasonable noise bandwidth if I use a small signal (like a 2N5770 or >>>> 918) and use the emitter-base junction as the zener. Most of them >>>> zener somewhere around 5 volts and that should be reasonable. >>>> Most of the comments regarding bandwidth using a "regular" zener >>>> centered around the rather large junction area necessary to carry some >>>> decent current; the junction of an RF transistor ought to be at least >>>> an order of magnitude (several??) smaller than that. >>>> Thoughts? >>>> Jim >>> One thing to keep in mind is the transistor is easily damaged when >>> zenered. You should do this with a current limited supply, say 100ua. >>> If you've ever done ESD testing or fuse testing, invariably the >>> reverse biased diode is the thing that is easily fried. When popping >>> metal fuses, you need to insure that the inductive kick of the zapper >>> is such that after popping the fuse, the diode junction gets forward >>> biased. This does dump current into the device, but that can be >>> controlled by the size of the capacitor used in zapping. For ESD >>> structures where there is no diode to the positive rail, the snap back >>> of the "off" nfet saves the parasitic diode junction. >> Be advised that the damage to a zenered transistor E-B junction is a >> time * current or dosage product, exactly as if it got radiation damage. >> Total dosage: a little over a long time = = a lot over a short time. >> Fairchild uA709s used in the Apollo got "nailed" by that. >> Turns out the company hired to test and burn them in did not know >> what an op amp was or how to test them or even burn them in despite a >> burn-in circuit in the data sheet! >> Their circuit zenered the inputs and that caused a failure mode >> during a mission. >> Fairchild engineers had to teach some basic electronics, and then >> advance to op amps and test methods as part of proof the 709s were not >> initially bad. >> The other part was a setup burning in NIB same date lot code parts in >> 2 batches: one using the nasty circuit and the other using the datasheet >> circuit. >> Oh yes; the cure is to anneal out the damage in an oven. > > Hello Robert, > > I did some experiments with low current reversed bias to the BE > junction of BC847. Even at low reverse current (10uA for several > hours), the HFE at low collector current (<10uA) drops significantly > after applying the reverse current. > > It looks like adding a resistor parallel to the BE junction as the HFE > at high current did not drop significantly. > > Does such dosage degradation to junctions also occur when reverse > biasing microwave schottky mixer diodes, or PN junction diodes? > > Best regards, > > Wim > PA3DJS > www.tetech.nl > please remove abc in case of PM. I have no experience with those diodes, but would guess they would have the same problem. |