Reply by Fred Abse January 5, 20122012-01-05
.wine/On Wed, 04 Jan 2012 11:31:41 -0700, Jim Thompson wrote:

> On Wed, 04 Jan 2012 08:28:09 -0800, Fred Abse > <excretatauris@invalid.invalid> wrote: > >>On Tue, 03 Jan 2012 10:47:26 -0700, Jim Thompson wrote: >> >>> It would be useful to have a model properly model BVceo breakdown. >> >>Zetex have a few models, ZTX415, FMMT415, etc.that don't come anywhere >>near datasheet performance, in LTSpice, at any rate. They might go in >>PSpice, I dunno, >> >>Convoluted designs involving "zener" models :-( > > What does it do in the real world? In PSpice, I did a sweep of VCE, with > floating base, and measured IC... breaks down/jumps up to about 700A at > VCE=300V, then becomes resistive at about 40mOhms. >
That's more or less what I see, using LTspice. I'm presently trying to reconcile performance with published figures. Breakdown at Ib=0 thru 3mA is horrible - 700mA vertical step before it goes negative slope - down to D_D5 in the subcircuit. Breakdown at Ib>3mA looks more like the proper shape. Simulated curve trace posted to a. b. s. e. I haven't had chance to get some and look at the "real world" performance, yet, but I don't suppose they'll have that step. As an exercise, I drew the subcircuit out. Here it is: Version 4 SHEET 1 1348 680 WIRE 1040 -304 1040 -400 WIRE 1104 -304 1104 -400 WIRE 1184 -304 1184 -400 WIRE -288 -208 -432 -208 WIRE -192 -208 -288 -208 WIRE -112 -208 -192 -208 WIRE 400 -208 -112 -208 WIRE 480 -208 400 -208 WIRE 592 -208 480 -208 WIRE 704 -208 592 -208 WIRE 880 -208 704 -208 WIRE 1040 -208 1040 -224 WIRE 1040 -208 880 -208 WIRE 1344 -208 1040 -208 WIRE -192 -176 -192 -208 WIRE 592 -176 592 -208 WIRE -288 -160 -288 -208 WIRE -112 -160 -112 -208 WIRE 400 -144 400 -208 WIRE 480 -128 480 -208 WIRE 480 -128 448 -128 WIRE 464 -80 448 -80 WIRE -288 -48 -288 -96 WIRE 176 -48 -288 -48 WIRE 192 -48 176 -48 WIRE 208 -48 192 -48 WIRE 304 -48 288 -48 WIRE 400 -48 400 -64 WIRE 400 -48 304 -48 WIRE 592 -48 592 -96 WIRE -432 -32 -432 -208 WIRE 1184 -32 1184 -224 WIRE 1184 -32 768 -32 WIRE 464 -16 464 -80 WIRE 592 -16 592 -48 WIRE 592 -16 464 -16 WIRE -192 0 -192 -96 WIRE -112 0 -112 -96 WIRE -112 0 -192 0 WIRE -32 0 -112 0 WIRE -16 0 -32 0 WIRE 64 0 48 0 WIRE 80 0 64 0 WIRE 176 0 176 -48 WIRE 176 0 160 0 WIRE -192 16 -192 0 WIRE 1184 16 1184 -32 WIRE 768 32 768 -32 WIRE 1184 32 1184 16 WIRE 1280 32 1184 32 WIRE 704 48 704 -208 WIRE 720 48 704 48 WIRE 1184 48 1184 32 WIRE 1280 64 1280 32 WIRE -32 96 -32 0 WIRE 720 96 -32 96 WIRE 880 96 880 -208 WIRE 992 96 880 96 WIRE 1104 96 1104 -224 WIRE 1104 96 1072 96 WIRE 1120 96 1104 96 WIRE -192 112 -192 80 WIRE -192 144 -192 112 WIRE 768 144 768 112 WIRE 704 160 704 48 WIRE 1008 160 1008 144 WIRE 1008 160 704 160 WIRE 1184 176 1184 144 WIRE 1280 176 1280 128 WIRE 1280 176 1184 176 WIRE 768 192 768 144 WIRE -32 208 -32 96 WIRE 720 208 -32 208 WIRE 1184 208 1184 176 WIRE 1184 224 1184 208 WIRE 1280 224 1280 208 WIRE -432 240 -432 32 WIRE -400 240 -432 240 WIRE -192 240 -192 224 WIRE -192 240 -400 240 WIRE -432 256 -432 240 WIRE 704 256 704 160 WIRE 720 256 704 256 WIRE 592 272 592 -16 WIRE 768 272 592 272 WIRE 1344 304 1344 -208 WIRE 1344 304 1184 304 WIRE 704 368 704 256 WIRE 1056 368 1056 144 WIRE 1056 368 704 368 WIRE -432 384 -432 336 WIRE -432 416 -432 384 WIRE 1184 416 1184 384 WIRE 1184 416 -432 416 FLAG 1184 16 9 FLAG 1072 96 8 FLAG 1184 208 7 FLAG -432 240 5 FLAG -432 384 6 FLAG -192 112 4 FLAG 304 -48 12 FLAG 192 -48 3 FLAG -112 -208 10 FLAG -192 0 2 FLAG 592 -48 11 FLAG 768 144 13 FLAG 1184 -400 16 IOPIN 1184 -400 Out FLAG 1104 -400 15 IOPIN 1104 -400 In FLAG 1040 -400 14 IOPIN 1040 -400 BiDir FLAG -400 240 5 FLAG 64 0 1 SYMBOL npn 1120 48 R0 SYMATTR InstName Q_Q1 SYMATTR Value Qmod1 SYMBOL res -448 240 R0 SYMATTR InstName R_R1 SYMATTR Value 100 SYMBOL res -176 240 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R_R2 SYMATTR Value 100 SYMBOL res 304 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R_R3 SYMATTR Value 100 SYMBOL res 176 -16 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R_R4 SYMATTR Value 500 SYMBOL res -208 -192 R0 SYMATTR InstName R_R5 SYMATTR Value 2k SYMBOL res 576 -192 R0 SYMATTR InstName R_R6 SYMATTR Value 2 SYMBOL diode -448 -32 R0 SYMATTR InstName D_D1 SYMATTR Value DZ20 SYMBOL diode -176 80 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D_D2 SYMATTR Value DZ500 SYMBOL diode -304 -160 R0 SYMATTR InstName D_D3 SYMATTR Value DZ200 SYMBOL diode 48 -16 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D_D4 SYMATTR Value DZ500 SYMBOL diode 1296 128 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D_D5 SYMATTR Value DZ300 SYMBOL cap -128 -160 R0 SYMATTR InstName C_C1 SYMATTR Value 20p SYMBOL sw 768 288 M180 SYMATTR InstName S_S1 SYMATTR Value Smod1 SYMBOL sw 768 16 R0 SYMATTR InstName S_S2 SYMATTR Value Smod2 SYMBOL sw 1088 96 M270 SYMATTR InstName S_S3 SYMATTR Value Smod3 SYMBOL voltage 1184 208 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 106 Left 2 SYMATTR SpiceLine Rser=0 SYMATTR InstName V_H1 SYMATTR Value 0 SYMBOL h 1184 400 R180 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 SYMATTR InstName H1 SYMATTR Value V_H1 50 SYMBOL e 400 -48 R180 SYMATTR InstName E1 SYMATTR Value 10 SYMBOL ind 1168 -208 M180 WINDOW 0 36 80 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName L_L1 SYMATTR Value 1n SYMBOL ind 1088 -320 R0 SYMATTR InstName L_L2 SYMATTR Value 2n SYMBOL ind 1024 -208 M180 WINDOW 0 36 80 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName L_L3 SYMATTR Value 2n TEXT -88 496 Left 2 !.MODEL Qmod1 NPN IS=3E-14 NF=1 BF=110 IKF=0.4\n+VAF=1900 ISE=1E-12 NE=1.6 NR=1 BR=7 IKR=0.2 VAR=75\n+ISC=1E-10 NC=1.9 RB=0.4 RE=0.1 RC=0.1 CJC=10.9E-12\n+MJC=0.347 VJC=0.476 CJE=82.6E-12 TF=1.3E-9 TR=2.3E-7\n.MODEL DZ20 D IS=1E-15 BV=20 IBV=100u\n.MODEL DZ200 D IS=1E-15 BV=200 IBV=100u\n.MODEL DZ300 D IS=1E-15 RS=0.1 BV=300 IBV=100u\n.MODEL DZ500 D IS=1E-15 N=10 BV=500 IBV=100u\n.MODEL Smod1 VSWITCH ROFF=1e10 RON=0.1 VOFF=4.3 VON=4.6\n.MODEL Smod2 VSWITCH ROFF=1e3 RON=1.0 VOFF=4.5 VON=9\n.MODEL Smod3 VSWITCH ROFF=1e10 RON=0.1 VOFF=20 VON=25 TEXT -80 464 Left 2 !.model ideal D (Ron=1n Roff=1T Vfwd=in) -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by Jim Thompson January 4, 20122012-01-04
On Wed, 04 Jan 2012 08:28:09 -0800, Fred Abse
<excretatauris@invalid.invalid> wrote:

>On Tue, 03 Jan 2012 10:47:26 -0700, Jim Thompson wrote: > >> It would be useful to have a model properly model BVceo breakdown. > >Zetex have a few models, ZTX415, FMMT415, etc.that don't come anywhere >near datasheet performance, in LTSpice, at any rate. They might go in >PSpice, I dunno, > >Convoluted designs involving "zener" models :-(
What does it do in the real world? In PSpice, I did a sweep of VCE, with floating base, and measured IC... breaks down/jumps up to about 700A at VCE=300V, then becomes resistive at about 40mOhms. ...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 | I love to cook with wine. Sometimes I even put it in the food.
Reply by Jim Thompson January 4, 20122012-01-04
On Wed, 04 Jan 2012 08:28:09 -0800, Fred Abse
<excretatauris@invalid.invalid> wrote:

>On Tue, 03 Jan 2012 10:47:26 -0700, Jim Thompson wrote: > >> It would be useful to have a model properly model BVceo breakdown. > >Zetex have a few models, ZTX415, FMMT415, etc.that don't come anywhere >near datasheet performance, in LTSpice, at any rate. They might go in >PSpice, I dunno, > >Convoluted designs involving "zener" models :-(
I have those models... rather complex for a zener. What do they do in LTspice? ...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 | I love to cook with wine. Sometimes I even put it in the food.
Reply by John Larkin January 4, 20122012-01-04
On Wed, 04 Jan 2012 08:28:09 -0800, Fred Abse
<excretatauris@invalid.invalid> wrote:

>On Tue, 03 Jan 2012 10:47:26 -0700, Jim Thompson wrote: > >> It would be useful to have a model properly model BVceo breakdown. > >Zetex have a few models, ZTX415, FMMT415, etc.that don't come anywhere >near datasheet performance, in LTSpice, at any rate. They might go in >PSpice, I dunno,
They work great. You can get a clean 25 kilowatt pulse out of a SOT-23. But don't expect a Spice model to be useful. Just try them. Good project for Sloman. John
Reply by Fred Abse January 4, 20122012-01-04
On Tue, 03 Jan 2012 10:47:26 -0700, Jim Thompson wrote:

> It would be useful to have a model properly model BVceo breakdown.
Zetex have a few models, ZTX415, FMMT415, etc.that don't come anywhere near datasheet performance, in LTSpice, at any rate. They might go in PSpice, I dunno, Convoluted designs involving "zener" models :-( -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by Jim Thompson January 3, 20122012-01-03
On Tue, 03 Jan 2012 09:37:08 -0800, Fred Abse
<excretatauris@invalid.invalid> wrote:

>On Mon, 02 Jan 2012 16:21:14 -0700, Jim Thompson wrote: > >> On Mon, 02 Jan 2012 09:52:41 -0800, Fred Abse >> <excretatauris@invalid.invalid> wrote: >> >>>On Sat, 31 Dec 2011 10:33:05 -0700, Jim Thompson wrote: >>> >>>> Accurately? Not easily. Spice has BV and IBV terms in the diode >>>> model. Some simulators, such as PSpice, support the Mextram BJT model >>>> which models avalanche in the _collector_: >>> >>>From the "Undocumented LTSpice" section of the LT Wiki: >>> >>>"Bipolar CB avalanche breakdown is modeled in the LTspice Gummel-Poon device: >>> >>> * BVcbo: C-B breakdown voltage. >>> * nBVcbo: breakdown emission coefficient ; default value = 1? >>> * TBVcbo1: linear temperature coefficient of breakdown voltage. >>> * TBVcbo2: quadratic temperature coefficient of breakdown voltage. >> >> I don't think that's truly avalanche. >> >>> >>>Bipolar BE breakdown is also in the LTspice Gummel-Poon device: >>> >>> * BVbe: B-E breakdown voltage. >>> * IBVbe: breakdown current at breakdown voltage. >>> * nBVbe: breakdown emission coefficient. " >>> >>>I haven't tried it (yet). >> >> And that ain't Gummel-Poon... it's LTspice... just like their "diode" >> model. >> >> > >Well, I've had a quick play, and I guess you're right:-(
LTspice has a lot of "finagles" that work _most_of_the_time_ when you're analyzing only switchers, but often give flaky results in analog or device-level applications. Since PSpice supports Mextram models, avalanching transistors, maybe I can figure out a ordinary Spice subcircuit match-up. It would be useful to have a model properly model BVceo breakdown. ...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 | I love to cook with wine. Sometimes I even put it in the food.
Reply by Fred Abse January 3, 20122012-01-03
On Mon, 02 Jan 2012 16:21:14 -0700, Jim Thompson wrote:

> On Mon, 02 Jan 2012 09:52:41 -0800, Fred Abse > <excretatauris@invalid.invalid> wrote: > >>On Sat, 31 Dec 2011 10:33:05 -0700, Jim Thompson wrote: >> >>> Accurately? Not easily. Spice has BV and IBV terms in the diode >>> model. Some simulators, such as PSpice, support the Mextram BJT model >>> which models avalanche in the _collector_: >> >>From the "Undocumented LTSpice" section of the LT Wiki: >> >>"Bipolar CB avalanche breakdown is modeled in the LTspice Gummel-Poon device: >> >> * BVcbo: C-B breakdown voltage. >> * nBVcbo: breakdown emission coefficient ; default value = 1? >> * TBVcbo1: linear temperature coefficient of breakdown voltage. >> * TBVcbo2: quadratic temperature coefficient of breakdown voltage. > > I don't think that's truly avalanche. > >> >>Bipolar BE breakdown is also in the LTspice Gummel-Poon device: >> >> * BVbe: B-E breakdown voltage. >> * IBVbe: breakdown current at breakdown voltage. >> * nBVbe: breakdown emission coefficient. " >> >>I haven't tried it (yet). > > And that ain't Gummel-Poon... it's LTspice... just like their "diode" > model. > >
Well, I've had a quick play, and I guess you're right:-( -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by George Herold January 3, 20122012-01-03
On Jan 2, 9:55=A0pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Mon, 2 Jan 2012 16:33:45 -0800 (PST), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On Jan 2, 1:15=A0pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Sun, 1 Jan 2012 08:57:38 -0800 (PST), George Herold > > >> <gher...@teachspin.com> wrote: > >> >On Dec 31 2011, 4:24 am, Bill Sloman <bill.slo...@ieee.org> wrote: > >> >> On Dec 31, 5:49 am, Robert Baer <robertb...@localnet.com> wrote: > > >> >> > Say one takes an E-B junction of a transistor or other diode and > >> >> > measures the (reverse) breakdown voltage over a wide range of cur=
rents
> >> >> > (say 5nA to 5mA), and assume there is no point or range where one=
sees
> >> >> > characteristics of negative resistance or of oscillation. > >> >> > Also say that voltage is about 9 volts. > >> >> > Q: is that zener or avalanche breakdown? > >> >> > Q: how does one make a SPICE model of such a proposed beastie? > > >> >> At nine volts, the breakdown is by avalanche. > > >> >> It happens in very small areas, and the transit times is picosecond=
s,
> >> >> so at low currents the avalanche self-extinguishes from time to tim=
e
> >> >> due to the statistical fluctuations in avalanche multiplication > >> >> process - sometimes a charge carrier gets through the avalanche reg=
ion
> >> >> without generating any new charge-carrier pairs. > > >> >> This isn't easy to model in Spice - it probably needs a current- > >> >> controlled random noise generator, but the real noise looks more li=
ke
> >> >> a series of Dirac spikes. > > >> >It's even 'worse' than that. =A0The noise changes 'character' as a > >> >function of current. > >> >Right near the 'knee' you go from random pulses to random steps. > >> >(random telegraph noise). =A0With more noise at low frequency.... But > >> >I'm not sure it's 1/f. > > >> A typical small 10-volt zener has a region where it will make noisy > >> sawtooth oscillations, 50 uA maybe from my memory. As current goes up, > >> you get the asymmetric erratic pulsing thing, decreasing in amplitude > >> as current increases. By the time you get to a few mA, it's nearly > >> symmetrical almost Gaussian wideband noise, a few hundred nV per root > >> Hz. > > >> >> For added extra complexity, you can throw in the fact that the > >> >> avalanche process generates light, and in glass-packaged zener diod=
es
> >> >> this can trigger other avalanches. > > >> >And that room light can get in and 'modulate' the avalanche. > > >> >> There was a thread on the subject here, many years ago - "Zener dio=
de
> >> >> oscillation" from July 7, 1997. > > >> >Yeah nice thread. > > >> >I find that for use as noise sources it's best to keep the current > >> >below the knee. > > >> If you want predictable noise with decent statistics and wideband > >> quality, keep the current up, 5 or 10 mA for a typical 1N758 type. > > >> John- Hide quoted text - > > >> - Show quoted text -- Hide quoted text - > > >> - Show quoted text - > > >Hi John, =A0Yeah I guess I was looking for repeatabliity. > >(I don't want to have to sort diodes...) > >I've got exactly the pulse into RC in the schematic I posted. > > >Adding two back to back gives this RC-interuptus signal. =A0Randomly > >spaced RC's going in both directions. > > >George H. > > That makes lots of signal, but it won't be repeatable and will have > rotten statistics. At higher currents, you get lower amplitude but > better noise. 300 nv/rthz is easy to amplify... it's hard to find an > opamp anywhere that bad. > > John- Hide quoted text - > > - Show quoted text -
Hmm, I don't know why, but the circuit seems to be very repeatable. We've sold ~150 units with this noise source in them and looking over my numbers I see rms voltages from 2.5 to 2.0 volts... with most of them at 2.2 Vrms. I have no idea of the 'physics' behind the numbers... or why other zeners vary so much. George H.
Reply by John Larkin January 2, 20122012-01-02
On Mon, 2 Jan 2012 16:33:45 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

>On Jan 2, 1:15&#2013266080;pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Sun, 1 Jan 2012 08:57:38 -0800 (PST), George Herold >> >> >> >> >> >> <gher...@teachspin.com> wrote: >> >On Dec 31 2011, 4:24 am, Bill Sloman <bill.slo...@ieee.org> wrote: >> >> On Dec 31, 5:49 am, Robert Baer <robertb...@localnet.com> wrote: >> >> >> > Say one takes an E-B junction of a transistor or other diode and >> >> > measures the (reverse) breakdown voltage over a wide range of currents >> >> > (say 5nA to 5mA), and assume there is no point or range where one sees >> >> > characteristics of negative resistance or of oscillation. >> >> > Also say that voltage is about 9 volts. >> >> > Q: is that zener or avalanche breakdown? >> >> > Q: how does one make a SPICE model of such a proposed beastie? >> >> >> At nine volts, the breakdown is by avalanche. >> >> >> It happens in very small areas, and the transit times is picoseconds, >> >> so at low currents the avalanche self-extinguishes from time to time >> >> due to the statistical fluctuations in avalanche multiplication >> >> process - sometimes a charge carrier gets through the avalanche region >> >> without generating any new charge-carrier pairs. >> >> >> This isn't easy to model in Spice - it probably needs a current- >> >> controlled random noise generator, but the real noise looks more like >> >> a series of Dirac spikes. >> >> >It's even 'worse' than that. &#2013266080;The noise changes 'character' as a >> >function of current. >> >Right near the 'knee' you go from random pulses to random steps. >> >(random telegraph noise). &#2013266080;With more noise at low frequency.... But >> >I'm not sure it's 1/f. >> >> A typical small 10-volt zener has a region where it will make noisy >> sawtooth oscillations, 50 uA maybe from my memory. As current goes up, >> you get the asymmetric erratic pulsing thing, decreasing in amplitude >> as current increases. By the time you get to a few mA, it's nearly >> symmetrical almost Gaussian wideband noise, a few hundred nV per root >> Hz. >> >> >> >> >> >> >> >> >> For added extra complexity, you can throw in the fact that the >> >> avalanche process generates light, and in glass-packaged zener diodes >> >> this can trigger other avalanches. >> >> >And that room light can get in and 'modulate' the avalanche. >> >> >> There was a thread on the subject here, many years ago - "Zener diode >> >> oscillation" from July 7, 1997. >> >> >Yeah nice thread. >> >> >I find that for use as noise sources it's best to keep the current >> >below the knee. >> >> If you want predictable noise with decent statistics and wideband >> quality, keep the current up, 5 or 10 mA for a typical 1N758 type. >> >> John- Hide quoted text - >> >> - Show quoted text -- Hide quoted text - >> >> - Show quoted text - > >Hi John, Yeah I guess I was looking for repeatabliity. >(I don't want to have to sort diodes...) >I've got exactly the pulse into RC in the schematic I posted. > >Adding two back to back gives this RC-interuptus signal. Randomly >spaced RC's going in both directions. > >George H.
That makes lots of signal, but it won't be repeatable and will have rotten statistics. At higher currents, you get lower amplitude but better noise. 300 nv/rthz is easy to amplify... it's hard to find an opamp anywhere that bad. John
Reply by George Herold January 2, 20122012-01-02
On Jan 2, 1:15=A0pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Sun, 1 Jan 2012 08:57:38 -0800 (PST), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On Dec 31 2011, 4:24 am, Bill Sloman <bill.slo...@ieee.org> wrote: > >> On Dec 31, 5:49 am, Robert Baer <robertb...@localnet.com> wrote: > > >> > Say one takes an E-B junction of a transistor or other diode and > >> > measures the (reverse) breakdown voltage over a wide range of curren=
ts
> >> > (say 5nA to 5mA), and assume there is no point or range where one se=
es
> >> > characteristics of negative resistance or of oscillation. > >> > Also say that voltage is about 9 volts. > >> > Q: is that zener or avalanche breakdown? > >> > Q: how does one make a SPICE model of such a proposed beastie? > > >> At nine volts, the breakdown is by avalanche. > > >> It happens in very small areas, and the transit times is picoseconds, > >> so at low currents the avalanche self-extinguishes from time to time > >> due to the statistical fluctuations in avalanche multiplication > >> process - sometimes a charge carrier gets through the avalanche region > >> without generating any new charge-carrier pairs. > > >> This isn't easy to model in Spice - it probably needs a current- > >> controlled random noise generator, but the real noise looks more like > >> a series of Dirac spikes. > > >It's even 'worse' than that. =A0The noise changes 'character' as a > >function of current. > >Right near the 'knee' you go from random pulses to random steps. > >(random telegraph noise). =A0With more noise at low frequency.... But > >I'm not sure it's 1/f. > > A typical small 10-volt zener has a region where it will make noisy > sawtooth oscillations, 50 uA maybe from my memory. As current goes up, > you get the asymmetric erratic pulsing thing, decreasing in amplitude > as current increases. By the time you get to a few mA, it's nearly > symmetrical almost Gaussian wideband noise, a few hundred nV per root > Hz. > > > > > > > > >> For added extra complexity, you can throw in the fact that the > >> avalanche process generates light, and in glass-packaged zener diodes > >> this can trigger other avalanches. > > >And that room light can get in and 'modulate' the avalanche. > > >> There was a thread on the subject here, many years ago - "Zener diode > >> oscillation" from July 7, 1997. > > >Yeah nice thread. > > >I find that for use as noise sources it's best to keep the current > >below the knee. > > If you want predictable noise with decent statistics and wideband > quality, keep the current up, 5 or 10 mA for a typical 1N758 type. > > John- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -
Hi John, Yeah I guess I was looking for repeatabliity. (I don't want to have to sort diodes...) I've got exactly the pulse into RC in the schematic I posted. Adding two back to back gives this RC-interuptus signal. Randomly spaced RC's going in both directions. George H.