RF Transistor Noise Source
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From: Robert Baer on 31 Dec 2009 04:59 Jim Thompson wrote: > On Tue, 29 Dec 2009 22:07:30 -0800, Robert Baer > <robertbaer(a)localnet.com> wrote: > >> Jim Thompson wrote: >>> On Tue, 29 Dec 2009 10:05:26 -0800, John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> 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 >>> "For some reason"? Try doping levels. >>> >>> ...Jim Thompson >> What level of a dope do you think i am, anyway?? > > You have already demonstrated that ;-) > > Just kidding! Just kidding! Just kidding! > > ...Jim Thompson ....we _do_ have our fun!
From: Robert Baer on 31 Dec 2009 04:59 Jim Thompson wrote: > On Tue, 29 Dec 2009 22:07:30 -0800, Robert Baer > <robertbaer(a)localnet.com> wrote: > >> Jim Thompson wrote: >>> On Tue, 29 Dec 2009 10:05:26 -0800, John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> 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 >>> "For some reason"? Try doping levels. >>> >>> ...Jim Thompson >> What level of a dope do you think i am, anyway?? > > You have already demonstrated that ;-) > > Just kidding! Just kidding! Just kidding! > > ...Jim Thompson ....where is that goat?
From: Robert Baer on 31 Dec 2009 05:06 Wimpie wrote: > On 30 dic, 07:03, Robert Baer <robertb...(a)localnet.com> wrote: >> 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. > > Hello Robert, > > Today I tested reverse current effects for a 1N4448 that I will use in > a small 12V to 300V converter. I will put several in series and would > like to know the effects of spread in reverse recovery time. > I supplied 14C of charge (7mAp, 1.3mA average, 130 kHz PRF) to the > diode. The differences in avalanche voltage, avalanche impedance and > reverse leakage were too small to detect in my simple setup (two > devices tested). * Have never fiddled with Trr, stored charge, etc so cannot comment usefully. 7mA is usually in the stable region, so ASSuMEing a sine drive, the diode could be in its stable region for up to maybe half of the reverse swing. > > In the product's lifetime, the diodes will be subjected to very low > overall reverse breakdown charge, so I think I will use the series > circuit of 1N4448. > > Probably one can do this for RF schottky diodes also (like BAT15). As > these have low capacitance and low break down voltage, they can be > used for a noise source. > > Best regards and good 2010, > > Wim > PA3DJS > www.tetech.nl > don't forget to remove abc in the Email address
From: Wimpie on 2 Jan 2010 08:27 On 30 dic 2009, 07:06, Robert Baer <robertb...(a)localnet.com> wrote: > John Larkin wrote: > > On Tue, 29 Dec 2009 02:27:37 -0800 (PST), Wimpie <wimabc...(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 > > 7mA; usually the minimum current which most zeners and reverse-biased > E-B junctions exhibit stability (ie: no negative resistance and noise). Hello Robert (and others), During the reverse recovery/breakdown measurements with the 1N4448 array, there were some non-repetitive phenomena. I further investigated this with a current limited source with good RF decoupling (100nA) and 150 Ohms impedance. Amazing results. Above about 20uA average reverse current, current spikes do occur due to instability. The measured rise/fall times are very likely less then 2.5ns (limited by my test setup). Peak current is 40mA (20uA average), with a lower longer lasting tail current. Even up to 8mA (that is 1W dissipation into a 1N4448), the instability remains, until it becomes stable due to self-heating. Peak current did not increase with increasing average current, but tail becomes longer and average PRF increases. When only self-heating is taken into account, 1.3mA reverse current (200mW diode dissipation) becomes stable after a while due to self- heating. When externally heating the diode (I guess to about 80 degrees), all instability disappears (also at lower currents). So without external heating, 1N4448 is not a good noise source. Best regards and a successful 2010, Wim PA3DJS www.tetech.nl Please remove abc when using PM.
From: Michael A. Terrell on 11 Jan 2010 21:58
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