Poor Man's LTZ1000 - Page 1
Forum section: electronics / general

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 06, 2017, 08:59:03 pm
content: D1 is emitter-collector junction of one of the transistors on a THAT300 (reverse breakdown = 5.4V)Q2 is another one on the chip.the remaining two can be used to implement die temperature sensor and a heater.i have measured the reverse break-down on THAT300 npn transistors ca. 5.4V (+.65 = 5.95V) and pnp transistors ca. 8.1V (+.65 = 8.75V)comments required from the learned members of the forum.regards.

author: Andreas
author_rank: Super Contributor
timestamp: June 06, 2017, 10:03:49 pm
content: Quote from: zhtoor on June 06, 2017, 08:59:03 pmReally emitter-collector?normally either base emitter reversed or collector shorted to emitter reverse biased against base.Other fears/comments:- normal zener against subsurface zener- noise? (I measured on a BCV61B switched as temperature compensated zener more than 20uVpp at around 5mA)- plastic package: humidity sensitivity and ageing?- Price/performance against a 1N829A temperature compensated zener?would be shure a interesting comparison against other references.with best regardsAndreas

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 06, 2017, 10:09:14 pm
content: yes. emitter collector breakdown, i was suprised also. (maybe someway to modulate the breakdown using some kind of bias on the base)regarding noise, we are talking about THAT300 transistors (spec: 0.85nv/RootHz).yes other factors should be considered. THAT380G bare die can be an interesting option.i think you have the equipment required to *really* characterize both ltflu-1ch and lt1k look-alikes (i say that with tongue-in cheek)have a go at it.regards and thanks.

author: Andreas
author_rank: Super Contributor
timestamp: June 07, 2017, 06:51:20 am
content: Quote from: zhtoor on June 06, 2017, 10:09:14 pmHello,Thats only the spec for the forward direction, the reverse direction is a different game.You will need a 1/f pre-amp anyway if you want to do volt nutting.(and its the cheapest part of the equipment).Before I will do some experiments with THAT I rather build my next batch of LTZ1000sAnd do some experiments with the 1N829A that I already have here.with best regardsAndreas

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 07, 2017, 02:41:42 pm
content: that is true, the noise spec is for the forward direction only,but a large area transistor may have a lower noise in the breakdown region.regarding noise testing, would you recommend something like hp 3561a / 3562a?regards and thanks.

author: Andreas
author_rank: Super Contributor
timestamp: June 07, 2017, 03:09:06 pm
content: Hello,all you need is a low noise band width limited (0.1-10 Hz) amplifier with about factor 10000 amplification,(depending on sensitivity of your scope)e.g. one of those:https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/And either a digital oscilloscope or a analog one together with a camera (10 secs exposure time).With best regardsAndreas

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: June 07, 2017, 03:11:59 pm
content: Try following forum guidelines.Check out the sticky here:https://www.eevblog.com/forum/metrology/(index)-metrology-section-quick-guide/msg1090954/#msg1090954there is a whole subsection pointing to low-noise measurement.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 07, 2017, 03:54:23 pm
content: With some low noise transistors there is the advice to avoid the break down region, as it might lead to damage to the transistor in the from of increased noise. So this is not at all promising long time stable operation. Another important point in the LTZ1000 is that the zener is a buried one and not a surface type zener. Likely even a more normal zener diode would be better than a transistor used as a zener. The break down voltage (and it's TC) of transistors is usually scattering a lot, so it would need quite some selection to find some with a suitable TC to allow compensation.Currently the best bet for a low cost, low noise reference would be the Chinese 2DW232 from a certain manufacturer. The noise is proven to reach very low values, at least after selecting good units. The operating current could be used to trim the TC and thus temperature regulation can be far less critical. So temperature regulation with an external heater is not such a big disadvantage. However long time stability is still an open question. In addition chances are high that the sensitivity to the stability of the current setting resistor will be higher than with the LTZ1000. So you might get away with a $1 zeners but need a $50 resistor to get low drift, if the zener itself is that stable at all.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 07, 2017, 07:25:46 pm
content: Do any of DH80417B(TI), SZA263(MOT) or the LTFLU-1CH(LT/FLUKE) have buried zeners?or are they standard "ref-amps"?it looks like all of them grew out of discrete zener/transistor combo used in 332B stuffed in an oven,i even saw a die-shot of an SZA263 clearly showing two separate dies (one for the zener, other for the transistor),whereas in the LTFLU both were on the same die. does anyone have a die-shot of the DH80417B which is earliest ofthese "ref-amps".regards.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 08, 2017, 05:55:56 am
content: Quote from: Kleinstein on June 07, 2017, 03:54:23 pmwhat would you say, for which of the following the avalanche breakdown would be deeper in the die-structure?1. collector-emitter shorted breaking down with the base, or2. collector breaking down with the emitter (base open circuit)if avalanche breakdown is deeper in (2) then, does it qualify to be called a "burried-zener"?an interesting observation: i tested a couple of S9018 and 2N2369 type transistors: emitter - base breakdown settles slowly with noisy readings,whereas emitter - collector breakdowns settle promptly. am i observing surface / deeper surface breakdowns ?a planar npn structure is attached for reference.regards.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 08, 2017, 06:46:25 pm
content: The LTFLU is a burried zener. The SZA263 likely too, as the performace is quite good.For a really good reference with a compensating diode the zener needs to be1) low zener resistance2) suitable TC (thus usually about 5.6-6.5 V)3) good stability and thus usually a sub-surface type4) low noise, especially low 1/f noiseA transistor makes more like a noisy zener that might (or might not) be in the right voltage range to get close to the right TC. It is still more like a surface zener, with breakdown at the surface. The collector - emitter break down is usually at much to high a voltage.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 08, 2017, 08:21:07 pm
content: Quote from: Kleinstein on June 08, 2017, 06:46:25 pmthanks again sir,and what about the performance of 332B with an ovenized individual transistor / zener connected as a refamp?i have actually measured collector-emitter breakdown of THAT300, ca 5.4 volts, also I have tested a smallbatch of 2N3904's with collector-emitter breakdowns of:-1. 6.3250v2. 6.3478v3. 6.1730v4. 6.1763v5. 6.2082v6. 6.3615v7. 6.5v8. 6.2365v9. 6.276v10. 6.286v11. 6.019v12. 6.294v13. 6.399vi have selected 2N3904 because it was introduced by motorola in the mid 60's (about time for their refamps), so i am kind of hopefulregards.