RF Transistor Noise Source
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From: Robert Baer on 30 Dec 2009 01:06 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 > 7mA; usually the minimum current which most zeners and reverse-biased E-B junctions exhibit stability (ie: no negative resistance and noise).
From: Robert Baer on 30 Dec 2009 01:06 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 > Name a few NPNs.
From: Robert Baer on 30 Dec 2009 01:07 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??
From: Jim Thompson on 30 Dec 2009 09:59 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 -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Help save the environment! Please dispose of socialism responsibly!
From: Wimpie on 30 Dec 2009 15:41
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). 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 |