RF Transistor Noise Source
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From: Phil Hobbs on 29 Dec 2009 02:59 On 12/29/2009 12:07 AM, Tim Wescott wrote: > On Mon, 28 Dec 2009 19:08:29 -0500, Phil Hobbs wrote: > >> On 12/28/2009 6:59 PM, Tim Wescott wrote: >>> On Mon, 28 Dec 2009 14:49:06 -0800, RST Engineering wrote: >>> >>>> On Mon, 28 Dec 2009 16:07:24 -0600, Tim Wescott<tim(a)seemywebsite.com> >>>> wrote: >>>> >>>>> On Mon, 28 Dec 2009 13:49:05 -0800, RST Engineering wrote: >>>> >>>> >>>>> It'll be good to know what your results are. >>>>> >>>>> Twenty years ago you could buy a noise diode from MA-COM (IIRC; it >>>>> may have been some other company), home-brew your own circuit to hold >>>>> it, then send it back to MA-COM for calibration. I don't know if you >>>>> still can. >>>>> >>>>> A noise diode was, of course, 'just a zener', optimized for use at >>>>> microwave frequencies. >>>> >>>> Noisecom and Micronetics are the only two I know of. Noisecom used to >>>> sell "factory seconds" to hams for pennies on the dollar but that >>>> practice seems to have gone by the wayside. They, as you noted, would >>>> also do a calibration of your design for a few bucks. Gone also. >>>> >>>> It will be fun to get back to experimenting with something where I >>>> don't have a real good idea what the answer is going to be. >>>> >>>> Jim >>> >>> I think it's Noisecom that I was thinking of. Dang; I should have >>> taken advantage while I could. >>> >>> I have thought that if you were building something low-noise enough you >>> could measure the noise figure with a pair of transmission lines >>> terminated in resistors: drop one into ice water (or dry-ice/acetone, >>> or LN2), and heat the other one up (boiling water, or a >>> not-quite-melted- solder heat furnace). Then switch between them. >>> With no current flowing through the resistors, you'd certainly know >>> their noise temperatures! >>> >>> >> A common approach in physics labs is to terminate the input with a 300 >> kelvin resistor, measure the noise, dunk the resistor in liquid >> nitrogen, and measure it again. Works great. >> > Goodness you keep the heat turned up -- or is that in the summer? > > It's about 293K in here now, because I can get comfort cheaper with a > sweater than by turning up the heat. > Nope, we reduce waste by keeping the house about 59 F in the winter (55 at night). So since it's 3 AM here, I'll see your 293 and raise you -8 kelvins. ;) Maybe the kids will move to Texas at some point. 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: Robert Baer on 29 Dec 2009 03:43 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. And the majority exhibit negative resistance and noise from sub-nanoamps to a few milliamps.
From: Robert Baer on 29 Dec 2009 03:56 miso(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.
From: Wimpie on 29 Dec 2009 05:27 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.
From: Tim Williams on 29 Dec 2009 06:23
"Phil Hobbs" <pcdhSpamMeSenseless(a)electrooptical.net> wrote in message news:4B39B6F7.1050504(a)electrooptical.net... > Nope, we reduce waste by keeping the house about 59 F in the winter (55 at > night). So since it's 3 AM here, I'll see your 293 and raise you -8 > kelvins. ;) Geesh! I try falling asleep at home without a space heater and wake up all sore, apparently from shivering all night. Has to be at least 68F in here to be comfortble, I'd guess. 'Course, at school I'm spoiled, because the hot water radiators are always cooking at a toasty 72 or so. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |