Author Topic: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x  (Read 234876 times)

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Offline GigaJoe

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #625 on: February 13, 2021, 05:08:40 am »
I have approx 20 diodes , running at 10-15 mA ; all of them was thermally isolated and selfheated to approx 80-90C . Run it for 2 years. I finally disassemble setup, and set 1 can ( 2 diodes in parallel ) with current  adjustment to minimal temp-co (approx 0.3-0.5 ppm\C )  It runs a week as prototype without any PPM changes.
 
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Offline pico61

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #626 on: May 13, 2021, 11:07:25 am »
Hello everybody,
after reading all the posts I wanted to try to experiment with 2DW23X zener references too.
I found a seller on AliExpress who offered them at a low price, around 18 € for 20 items, including shipping.
I had bought 20 2DW232s but, after the purchase, he informed me that he only had 2DW235s available.
The latter, according to the datasheet, should work with a nominal current of 15mA, in my opinion too high due to self-heating but then reading what zlymex wrote, I bought them anyway.
After about a month, they were delivered to me.
The first thing I checked was the presence of the diamond symbol on the case.
I started testing using a Keithley 220 current source and a Fluke 8846A multimeter.
I state that at least in this phase I am only interested in verifying stability rather than low noise, not having suitable instrumentation to evaluate it.
At first I set the generator to 15mA.
I tried to heat the zener to a temperature of about 50 ° C. I detected a large variation in the voltage, then I tried to increase the current in steps of 1 mA up to 30mA but without significant changes in the Tc. So I tried with lower currents, always with steps of 1 mA, up to 5mA.
I found two things: the first is that around 7mA the TC decreased (but I have not been able to investigate further) and the second that over 10mA the zener tended to self-heat.
Then, I wanted to try lowering the current to just 2mA. Amazed I discovered that the Tc was almost zero! I tried to heat it up to 80 ° C (from 23 °) and I got a variation of less than 100uV. I tried again to reduce the current down to less than 1.5mA and I discovered a feature: the Tc is reduced to zero with a positive value (+ temperature, + voltage) up to a current of 1.56mA. With lower values ​​it becomes negative (+ temperature, - voltage). For this it was easy to discover the point at zero TC.
The detected voltage, at a current of 1.56 mA, was 5.24792V.
I tried to leave the 2DW235 plugged in for twenty four hours and the variation was 20uV (5.24794V - less than 4ppm) with a room temperature going from 23 to 25 ° C. However I can't be sure if the variation is due to the zener reference or the F8846A or due to current variations of the K220.
I tried to switch it off and then back on several times, even several hours later, and the maximum variation was only +/- 10uV (+/- 2ppm).
I have some questions:
- has anyone already detected this behavior of the 2DW23X?
- could they be used with out-of-specification currents? And the behavior regarding noise at such low currents?
« Last Edit: May 13, 2021, 11:21:57 am by pico61 »
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #627 on: May 13, 2021, 01:16:22 pm »
A voltage of 5.25 V to get a low TC suggsts that this would be for only 1 zener, and not with both zeners in seires in the usual compensation way.  It is normal to get a low TC for only 1 zener at a much lower current that for the series connection.
 

Offline pico61

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #628 on: May 13, 2021, 01:33:25 pm »
A voltage of 5.25 V to get a low TC suggsts that this would be for only 1 zener, and not with both zeners in seires in the usual compensation way.

Yes the experiments were carried out only on one of the two zener in the case and only on three, of the twenty 2DW235 purchased, with voltages that varied between them by a few tens of mV.
 

Offline LHT5631080

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #629 on: June 15, 2021, 06:37:24 pm »
    Someone at 38HOT forum pointed out that it (2DW232) is more suitable for use under constant temperature conditions. The test conditions given in the specification are 25 degrees Celsius-75 degrees Celsius, which seems to indicate that it is not suitable for normal temperature use. Don't try to use a current far beyond its rated current in order to expect a TC.
    Under certain temperature conditions (for example, 50 degrees Celsius), a lower temperature coefficient can be obtained by adjusting the current around 5 mA-the test results of POCO61 have actually demonstrated this. 38HOT forum netizens make a voltage reference, and the 2DW232 internal 2 voltage regulators used in it are used in series instead of using one of them.
« Last Edit: June 15, 2021, 06:40:31 pm by LHT5631080 »
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #630 on: June 15, 2021, 08:49:34 pm »
Using a stabilized temperature makes a lot of sense, as the 2nd order TC is relatively high. Even if one adjusts the current to get a low linear TC, this is only valid for a limited temperature range.

The 2DW232 have widely scattering parameter. So it is not like an 1N829 - more like a random pic from 1N821 - 1N827. For the series configuration it may just need a lot (too much also at a higher temperature) of current to get a low TC. Those diode are better used as single Zener with a lower current to get a low TC this way. So it depends on the units if they are more suitable to use as a single diode at a relatively low current or with 2 in series with compensation. There can be some that do not work well in both mode (e.g. need >10 mA in series and <<1mA as a single diode).
So ideally one would get better screed ones, so one knows which circuit there is suiteable for. The situaltion with the 1N821 / 823 is also not ideal - it may be nice to know if the TC is positive or negative, they are likely testing them and could keep them separate.
 

Offline julian1

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #631 on: May 01, 2022, 10:52:41 pm »
Resurrecting an old thread. Here's an attempt to use an instrumentation amplifier to pull out the on-die temperature of the top forward-biased diode - and then use that feedback to control the heater loop.

By breaking jumper R201, it is somewhat convenient to dial in the heater set-point to match TC0 using a DC sig-gen, calculate the required divider resistors (R202,R201) to fix it, and then reconnect the jumper.

The best noise figures I see are about 600nV p2p, 0.1-10Hz. For comparison my 10000x lna reads near the high end of the ltz1000 spec - 1.8 to 2uV for my ltz1000 references.

There appears to be some variation between 2dw232 parts from the half dozen I tested. And some are much worse.

Using opa2277, foil resistor for current limit, and thin-film for dividers.

I wish I could get hold of some of the parts that show <350nV pp, similar to the original forum posts.
 
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Offline julian1

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #632 on: May 01, 2022, 11:28:05 pm »
The epoxied resistor looks a bit agricultural, but work ok.  Someone should tell the factory, they could add a 200R heater to the die, exercise a bit more selectivity over their batch processes, and sell units for 50-100 dollars each
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #633 on: May 02, 2022, 08:37:20 am »
Only 10 Ohms to set the zener current is not ideal. This makes the circuit quite sensitive to the offset of the OP.

An integrated heater would be nice, though I would prefer a zener diode over a resistor, as this can be more effective at the low power end. A more linear heater response also helps with regulation, especially if the distance from heater to sensor is a bit larger and thus a more difficult control loop.
 

Offline julian1

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #634 on: May 02, 2022, 10:20:02 am »
Sensitivity to op input offset will make the reference more susceptible to drift/temperature drift. But will not influence low-frequency noise, I don't think. I will change it before any attempt at long-term characterization is done, but that's probably unlikely at the moment.   

If I could find a part below 450nV pp, then opa2209/opa2210 would be worth substituting.

A zener as heater would be even simpler for manufacturing, as the factory could merely replicate the existing back-to-back diode structure twice on the same die.    
 

Offline analityk

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #635 on: June 02, 2022, 08:50:27 pm »
Today i have reveived my 20 pieces od 2DW236.

Diodes have this magic diamond picture and date (15-4 if it is date). There was a trace after the dot was removed.

Any way i was give it firslty something around 5mA and tempco was strong negative and voltage rise with temperature rise.

But with only 1.8mA the voltage drop on diode (series connected two diodes) was near constant and it was 6.46V. As long as it is a bit sad resolutnion and precision this voltage was constant even if i freeze this diode (down to ~-45 degree of Celsius) from room temp (23 deg. C) - voltage was stable in temp range 70 deg. C. It is not a fluke i guess. I was warm this diode after freeze with solder tip (but carefully) up to ~60 deg. C and voltage droped about 0.01V.
So this 1.8 mA for this piece is nearly zero tempco current.
I have one OPA189ID and one LT1028 (from low noise opamps under hand). Whih of them two should be better?

Did anyone check mass of this diode?

Sincerely
 
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Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #636 on: June 02, 2022, 09:17:32 pm »
A current of only 1.8 mA to get a low TC is a reasonable value. It may not be the absolute lowest noise, but could still be a good. I would prefer it over a diode that needs > 10 mA.  The lower current makes temperature stabilization more practical.

Which of the OP-amps is better depends on the circuit. The LT1028 is a bit limited by a minimum gain needed to be stable and the relatively high current noise, which makes it suitable for a relatively low impedance circuit only. So not really suitable for amplification of a AC coupled lower frequency signal.

For just creating a auxiliary voltage to drive the current a simpler OP, like OP07 or OPA202 would be the more obvious choice, but the OPA189 would work, but is overkill.
 

Offline julian1

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #637 on: June 02, 2022, 09:44:17 pm »
The current needed to hit TC0 with most 2dw2xx examples that have been tested, is quite high. See the second figure/chart from here,
http://hololaser.kwaoo.me/electronics/2DW23x.html
The tradeoff is that higher current drives down zener noise generally.



 
« Last Edit: June 02, 2022, 09:52:56 pm by julian1 »
 
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Offline analityk

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #638 on: June 02, 2022, 10:40:27 pm »
So i have started looking for constant tempco from 5mA but it was not present.

I have read all this topic before and i remember someone gives simillar results. Lower current mean lower power dissipation and smaller temperature gradients. In my case even 500nV noise on 10V signal propably is far away from my need and measurements possibilities, so it is always a bit more eco.

I have buy more OPA189's when it was on stocks so i have plan to use it in precision circuits.

As long as i looking for other (cheaper) OA i can't find any with lower input bias current with respect to noise in low frequency region. And it Vos and current consumption is impressive.

Sincerely
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #639 on: June 03, 2022, 07:50:11 am »
The choice of OP-amp really depends on the use:
To provider the zener current, an OP07 or similar is good enough and even has some advantage over an AZ type.
To amplify a AC coupled signal to measure 0.1 to 10 Hz noise, there are several options, like LT1037, OPA207 as low noise BJT based OPs with not too much current noise,  OPA140 or related as JFET amplifiers with low 1/f noise and AZ OPs like OPA189 or OPA388 (no need for a higher supply or super low bias).
To amplify the ref to a stable 10 V a AZ OP like the OPA189 or MCP6V51 / LTC2057 are good, a precion BJT base OP should still be good enough (lower noise and drift than the ref. and resistors).
To amplify the difference of 2 such references, one could consider an instrumentation amplifier, but there are other options too, depending on the supply / ground point used.

With the current of low TC relatively low, there is in theory the option to use only part of the forward bias diode (with an extra divider, like 1:3) and this way shift the point of zero TC to a somewhat higher current if wanted. I had long thought about a way to shift the zero TC point to lower current. A slight shift towards lower current could be obtained with a resistor in parallel to the forward diode. The shift is not really large (so no way to get from 25 mA to 10 mA), more like a way for a fine trim for the zero TC temperature.

With the diodes individually accessible, the obvious way to get a really stable reference would be to use this to measure the diodes temperature and add a small oven for the reference. So there is no need for a very accurate adjusted current, just enough to get a resonable low TC (e.g. < 5 ppm/K or some 10 K away from the optimal temperature) so that the demands on the oven is not very high.
 

Offline analityk

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #640 on: June 09, 2022, 03:30:53 pm »
Input offset voltage drift:
OPAx140 = 350nV/K;
OPA207 = 200nV/K
OP07 = 500nV/K;
LT1007 = 200nV/K;
OPAx189 = 5-10 nV/K;

My 2DW236 give 6.477V in zero tc region of operation and consume near 1.8mA. I should place 1k8 resistor for current set assuming opamp give exacly 10V. Voltage drop on this resistor is equal 3,523V. If i use 100ppm resistor and assume constant zener current (and virtualy zero change of zener voltage) temp. change of this resistor from 20 to 30 deg. of Celsius cause change of current about only 4.5 nA.
During this time OP07 give me voltage change (Vos) equal 5uV. It is 1000 times more and i think it is most important factor in this circiut.

Am i right?
« Last Edit: June 09, 2022, 04:24:38 pm by analityk »
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #641 on: June 09, 2022, 04:01:45 pm »
If the current is well adjusted for a low TC, one would have the residual TC for the zener slightly below 1 ppm/K. 1 ppm of 6.5 V are still 6.5 µV. So even with a pretty well trimmed zener current the more critical TC is from the zener itself.  This does however change, if the temperature of the diode is regulated (especially to get rid of the square part of the temperature dependence).

With the amplifier and also the resistors it is not so much about the TC. The more important factor is the long time drift and possible the very low frequency noise.
If the TC of the 10 V output is critical I would consider to have the resistors also in the oven for the reference. Just for suing the 10 V as an auxiliary voltage to provide the current this is not really needed.
I think the calculation of the current change is wrong, should be more like 1.8 µA change in current from a 1000 ppm change in the resistor. So a somewhat better resistor would be a good idea.
The differential restance of the zener would provide about a 100 fold attenuation of the relative curent change. So 1000 ppm from the resistor would translate to around 10 ppm or some 65 µV for the voltage.
So consider the OP07 to be about as "good" as resistors in the 10 ppm/K range.
 
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Offline analityk

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #642 on: June 19, 2022, 09:48:35 pm »
Hello,

i have build "prototype" from schematic included in first post in this thread. Simple 3 resistor, opamp and 2dw236. With small pot it is possible to set output voltage at 10,00V (nah, i know but). Next step was looking this voltages on oscilloscope (basic noise level etc).
You can see all in pic rel.
Supply voltage i take from SMSP psu (~22V) especialy for this prupose. Yellow "line" is power supply (50mV per div), blue line is output voltage from opamp - in this case is half of OPA2189. (second half is shorted and grounded).
Where is all PSRR?
I've add 4700uF/50V cap on input supply.
Did this one 10nF cap can destroy all this PSRR of opamp? Or in other case what i have missed or not understand in this circuit?

I have used all 0,1% 15 ppm resistors with one 100 ohm potentiometer.

Sincerely.
Analityk
 

Offline iMo

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #643 on: June 20, 2022, 04:09:54 pm »
Hello,

i have build "prototype" from schematic included in first post in this thread. Simple 3 resistor, opamp and 2dw236...
Where is all PSRR?
..


It could be you have there a grounding problem or your probes are grounded on a not good place (getting a pickup via a gnd loop).
I've put your schematics into LTSpice (with an OP07) and in the Vcc injected 100mV noise will be attenuated pretty well at the output..
PS: not sure this is an ideal schematics for the intended purpose, imho..
« Last Edit: June 20, 2022, 04:15:32 pm by imo »
 
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Offline MiDi

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #644 on: June 20, 2022, 08:14:52 pm »
Supply voltage i take from SMSP psu (~22V) especialy for this prupose. Yellow "line" is power supply (50mV per div), blue line is output voltage from opamp - in this case is half of OPA2189. (second half is shorted and grounded).
Where is all PSRR?
I've add 4700uF/50V cap on input supply.

Your probes should be in 10x mode and scope should be set accordingly.
A picture of your setup could help, the OPA2189 should be bypassed with 100nF ceramic close to it.

Jellybean SMPS is not recommended for precision/low noise circuits, for test you could use 2x9V batteries.
SMPS have leakage current to earth and finding path through scope probe.

The added 4700µF cap does not reject SMPS spikes much, ferrite beads followed by 100nF ceramic caps will do much better, but will not help with gnd loop.
Shielding the circuit e.g. with a cookie box is recommended.
 
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Offline analityk

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #645 on: July 31, 2022, 10:35:34 pm »
I have discovered what was mentioned here earlier, the temperature coeficient is current dependent but it is not only one point with one specyfic current but if the current is higher the higher (and narrower) is zero-TC region.

This mean there is possible to fix one setup current for 2DW23x and next step is find working temperature. I have build easy oven for my 2dw23x with one NTC and one resistor (THT, 0.25W, 270R, thermaly connetced by thermal tape) switching on/off by bc337, and one copmarator to drive transistor. If thermal properties of diode insulation is good it should can work in near constant temperature and this temp. can be setup by single and cheap resistor.

I measure it with my siglent sdm3065x bench DMM and what i can see - is need around 20-30 minutes to stabilize itself. In this picture you can see volatage from my ovenized 2DW236 but it work uninterrupted since 4 hours and measurements was started soon after turn on my DMM.

Im supposed all initial drift was introduce by siglent. Rate of change of voltage from 2dw236 was at least one row smaller.

This circuit have 3.2 uV std deviation. For few test (device was turned off/on and measure after one hour later) i take values in range from 10.00087 up to 10.00094V and this prototype is mostly in air-wire style.
 
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Offline iMo

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #646 on: August 02, 2022, 06:10:40 pm »
You should wait at least 1-2 hours for warming up your DMM (I do ~3 hours with my 34401A with built-in thermometer). Also I would add a transistor at the opamp's output in order to buffer the diode's current (and thus to off-load the opamp). The opamp's feedback capacitor should not be higher than 1nF otherwise the PSRR goes down. With 10V out I would expect <0.1uV standard deviation in your setup (battery powered).
« Last Edit: August 02, 2022, 07:21:34 pm by imo »
 

Offline Noopy

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #647 on: September 15, 2022, 12:02:26 pm »
I have taken some pictures of the 2DW234. In the first place I tried to find some information about these reference diodes. I did a fast run through this topic. A lot of information isn´t new and I hope I got everything right.








There is this paper describing the 2DW14 - 2DW18 and the 2DW213 - 2DW216. Google translator is a big help but the text is still hard to read. It seems like these are temperature compensated buried zener diodes.

There is more than one manufacturer for these diodes. The standard SJ 50033/151-2002 describes the 2DW14 - 2DW18 as "low-noise silicon voltage-regulator diodes". The standard SJ 50033/150-2002 describes the 2DW213 - 2DW216 as "silicon voltage-regulator diode". So the low noise parts are the 2DW14 - 2DW18!






Also in the China Academic Journal is a paper whose title Google translates as "A high quality and low cost voltage reference - 2DW230-2DW236 reference voltage diode." It compares the 2DW230 - 2DW236 diodes built by different manufacturers with other temperature-compensated zener diodes, including a 1N825A from Motorola.

There are parts with significant noise and drift over time. The "Sapphire" brand from the Shanghai 17th Radio Factory (first line), which the publication deals with in particular, offers particularly good characteristics.




With 40 parts they had 34 diodes drifting less than 120µV/100hr.




Specifications for the "Sapphire" brand.






I bought some "Sapphire" 2DW234 and 2DW232 from ebay. The following pictures are taken from different 2DW234 and 2DW232. In principle they look all the same.




The standard SJ 50033/150-2002 specifies the mechanical construction and the interconnection of the diodes. The colored dot on the side shows the polarity of the temperature compensated zener diode.




The case contains an elongated die and a white potting, which often can be found in Chinese transistors. The metal crumbs that are produced when opening the case stick quite well to the potting.






The potting does not always completely cover the die.








The dimensions of the die are 0,74mm x 0,36mm. There are two square zener diodes whose anodes are connected via the die.

The publication on 2DW diodes roughly describes the manufacturing process. According to this it is just a p-doped substrate into which just one n-doping is introduced. It seems to be impossible to build up the special structure of a buried zener with such a process (like the one in the ADR1000: https://www.richis-lab.de/REF19.htm#buriedzener).




In the left picture the aluminum was removed with hydrochloric acid. In the right picture the silicon oxide was dissolved with hydrofluoric acid. There is no special structure visible.  :-//




As you know the junction of a Z-diode lights up during operation. If we take a close look at the 2DW234 no luminescence can be seen. Apparently the junction is located underneath the metal layer.




The quality standards are apparently not too high. On one 2DW234 they had three tries with the bondwire.




Even more surprising, however, are the remains of other semiconductors found in six of seven packages. Old packages seem to have been reused here.  :o






It is the remains of a double transistor. The degraded edges are probably due to a removing process. What could not be removed was covered with potting.






Here we find a slightly more powerful transistor, which was obviously fixed with too much solder.






Not too much remained of this die. It was probably a more powerful transistor too.






In these two packages just the solder of the die attach remained in the package.


https://www.richis-lab.de/REF23.htm

 :-/O

Offline SilverSolder

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #648 on: September 15, 2022, 04:11:27 pm »

It's amazing how far some people will go with recycling / reuse!

 

Offline Gyro

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #649 on: September 15, 2022, 07:41:56 pm »
Maybe it's a 'lucky charm' - after all, what are the chances of having two different dodgy dies in the same package!  :D


P.S. Somewhere back in this thread is an example of two discrete zeners crammed into one of these packages (with a loose lid).
« Last Edit: September 15, 2022, 07:47:22 pm by Gyro »
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