Matched transistors for analog experiments - Page 1
Forum section: electronics / projects

author: RoGeorge
author_rank: Super Contributor
timestamp: February 13, 2024, 09:04:10 pm
content: Looking for factory matched BJT transistors, but I wouldn't mind finding some matched JFET or MOSFET either. They are for experimenting with long tails, current mirrors and alike. This is hobby level, so I don't want to break the bank buying $30/1pair of famous NOS part numbers.I've looked at mouser, and for 'transistors array' it returns all kind of darlington and drivers and H bridges. When searching for 'matched transistors' there are only 3 part numbers, decent price (less than $0.5-$1/pcs), but they are all pnp pairs.There are some ROHM pairs from their THAT300 series, advertised in a mouser "what's new" page, but they do not appear as products for sale, only advertised and no link to buy.The matched transistors are for casual learning and experimenting with discrete analog IC-like structures. Required specs are as good as possible, but at very low cost, less than $1/pair.- What paired transistors part numbers to look for, and what search term to use?- Will factory matched be better matched than hand-matching from a casual bag of 20..50 THT discrete transistors of the same type?

author: Andy Watson
author_rank: Super Contributor
timestamp: February 13, 2024, 09:18:43 pm
content: Quote from: RoGeorge on February 13, 2024, 09:04:10 pmTry "dual transistor"In my limited experience, you will struggle to match individual transistors to the same level that is easily and readily obtained with transistors that are on the same die. I believe CA3046 are still available.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 13, 2024, 09:24:05 pm
content: There are a few cheap dual BJTs (e.g. SOT23-6). They offer some degree of matching, though not as good as the higher cost SSM2212 or THAT300.Examples are FMBM5551, NST45011.THT duals are rare however and can get expensive.For JFETs there is the SK2145 as the prime candidate for a cheap pair - though already connected source to source. There are also some more dual JFETs, but not all offer good matching, at least not guaranteed.For high performance the JFE2140 is a candidate to look at, though more in the $4 range, still not super expensive.Chances are manual matching could be more accurate (at least for the parameters tested), if one starts with transistors that are quite uniform or accepts a low yield (e.g. only use the best 1 or 2 pairs out of 20).

author: magic
author_rank: Super Contributor
timestamp: February 13, 2024, 09:36:43 pm
content: Quote from: RoGeorge on February 13, 2024, 09:04:10 pmThis virtually rules out monolithic pairs, unless you manage to find some obsolete transistor arrays on eBay or similar sites. I think I have seen a 5-NPN array for $2 once. You can probably forget PNP.If you look at dual transistors in SOT23-6, some of them are offered with ±2mV offset guarantee. IIRC suppliers were NXP and Diodes and part numbers were quite generic: xxx847xx, xxx3404xxx, xxx5551xxx or their PNP analogs. I imagine these may be very handy for mass production.The Vbe spread in a bag of 2N3904/3906 or BC847/857 from decent manufacturers like Fairchild (now ON semi, I suppose) is very small, a few mV. You will easily harvest multiple pairs with 2mV or even 1mV offset. Test with DMM diode mode, one probe on E and one on BC shorted together. Or get the AVR transistor tester, which will also show β.I hope you know that 2mV matching only holds if internal junction temperatures stay within 1°C of each other. Only realistic if power dissipation is very low or equalized.

author: djsb
author_rank: Super Contributor
timestamp: February 13, 2024, 09:38:27 pm
content: Alfa in latvia still make a LM194/394 equivalent. They are discussed in this threadhttps://www.diyaudio.com/community/threads/lm194-lm394.333623/They can be bought from Erica synths or Thonk in the UK.

author: exe
author_rank: Unknown
timestamp: February 13, 2024, 09:39:31 pm
content: For bjt: try BCM846 and other BCM* parts.

author: moffy
author_rank: Super Contributor
timestamp: February 13, 2024, 09:46:44 pm
content: Got this result at Mouser using the term "matched transistor":https://au.mouser.com/c/?q=matched%20transistor&sort=pricingSurprisingly good matching for low cost pairs, 2mv Vbe and 2% hfe.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 13, 2024, 11:57:14 pm
content: Quote from: RoGeorge on February 13, 2024, 09:04:10 pmAs above in #6, use matched. They can be as good as 2mV and 2%. TI have a new matched pair JFET.Here are some from my local drive - note you can also get 40V / 6A parts matched.JFE2140_TI_JFET_Dual_40V_0p9nV_4mV_Match_1d64NSS40300MD-D_DualPNP_Match_40V_6A_SO8_HFEt230_2ANSS40301MD-D_DualNPN_Match_40V_6A_SO8_HFEt320_2A2304140030_Nexperia-PMP5201Y-115_C553005_MatchPNP_45V_2mV_2pc_SOT3631810261910_Diodes-Incorporated-DMMT5401-7-F_C154733_MatchedPNP_150V_2pc_SOT26bcm847bs_diotec_Dual_Match_2mV10pc_SOT363PMP4201V_DualNPN_Matched_2pc2mVQuote from: RoGeorge on February 13, 2024, 09:04:10 pmI would expect a lot better, than a bag-match.It will take you a while to find 2% HFEand2% VBE matches.Parts from 'the same reel' can be expected to be somewhat matched. I think Infineon had an appnote on the spreads.

author: David Hess
author_rank: Super Contributor
timestamp: February 14, 2024, 02:25:52 am
content: Texas Instruments makes a monolithic matched JFET based on their more recent high voltage JFET process available as the JFE214:https://www.mouser.com/ProductDetail/Texas-Instruments/JFE2140DR?qs=A6eO%252BMLsxmQVeRIGZCabaw%3D%3DDigikey and Mouser now sell matched MOSFETs and JFETs from Linear Systems, but apparently not their bipolar transistors. These are the real thing:https://www.mouser.com/c/?m=Linear%20Integrated%20SystemsCalogic makes matched transistors but they are not as easily available.If you buy 10, 25, or 100 transistors in bulk, then you can match them pretty well yourself with some test circuits. This will be good enough for hobby and student work. Glue pairs together for temperature tracking.

author: moffy
author_rank: Super Contributor
timestamp: February 14, 2024, 02:52:02 am
content: Quote from: PCB.Wiz on February 13, 2024, 11:57:14 pmThe JFE2140, a dual matched low noise JFET, available and a reasonable price, nice.

author: mawyatt
author_rank: Super Contributor
timestamp: February 14, 2024, 03:08:56 am
content: Quote from: David Hess on February 14, 2024, 02:25:52 amRemember way back when there were small metal clips that held 2 TO92 transistors face to face to create a "Matched Pair" from select devices. One could use a "C" chip made from heavy gauge bare wire also, or as you indicate just Super Glue them together.Best,

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: February 14, 2024, 02:18:19 pm
content: Japanise transistors are labeled with gain group if all numbers on the parts are the same from the same manufacturerthey are matched parts.Can not say the same for US or Euro parts.Jeff

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2024, 02:43:47 pm
content: NPN or PNP?I've seen the PNP, DMMT5401 used in ideal diode circuits, but the data sheet doesn't specify matching. Presumably it's pretty good. The NPN version is DMMT5551.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 14, 2024, 03:27:34 pm
content: Both types.Also, thank you all for suggestions.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 14, 2024, 05:06:21 pm
content: Quote from: Jeff eelcr on February 14, 2024, 02:18:19 pmFor the gain groups it depends. One can get some type in gain groups or without. The naming can be different depending on the types : E.g. with an extra number like -10, -16,-25, -40 for the BD135 or BC337 or a letter like BC547A,B,C or with Japanese sometimes color dots, sometimes written as a letter on the bag (e.g. O,G,Bl) or when ordering.The matching in the gain (or threshold with FETs) is often not that tight. One may want more than that in some applications.It also depends on the application what parameter should be matched (e.g. VBE, hfe, Vsat, Vearly) though to a large part the parameters are quite correlated for parts from the same batch.Even if the dual parts don't specify matching, it often is quite good, but may want a check.

author: magic
author_rank: Super Contributor
timestamp: February 14, 2024, 05:19:18 pm
content: I pulled 5 completely random CDIL 2N2222A from my parts box and tested them for Vbe and hFE on a DMM.That's one of the cheapest TO92 transistors in the world from a cheap Indian manufacturer, they cost pennies at TME.Vbe: all five were 649~651mVhFE: four were 160~165, one was 167IMO thermal matching (including during selection) is more likely to be an issue in practice than production variation.

author: mawyatt
author_rank: Super Contributor
timestamp: February 14, 2024, 06:24:55 pm
content: Quote from: RoGeorge on February 13, 2024, 09:04:10 pmSince this is a learning experience doesn't this give you anexcusenecessityrequirementfor a curve tracerMaybe use the technique you posted about controlling your PS for the Curve TracerOr better yet, anexcusenecessityrequirementfor a pair of SMUsBest,

author: HalFoster
author_rank: Frequent Contributor
timestamp: February 14, 2024, 06:51:36 pm
content: I use AD's MAT02 quite often and have always had very good results.Hal

author: David Hess
author_rank: Super Contributor
timestamp: February 15, 2024, 12:24:54 am
content: Quote from: HalFoster on February 14, 2024, 06:51:36 pmThe Analog Devices' MAT series are great, except for the price, and the PNP parts seem to be missing.Quote from: Kleinstein on February 14, 2024, 05:06:21 pmThat is my experience. Within the same lot of the same part, matching for one parameter largely matches for the others.

author: twospoons
author_rank: Frequent Contributor
timestamp: February 15, 2024, 03:59:52 am
content: Don't bother hand matching individual parts, its a waste of time. The two devices need to be thermally matched as well - so at very least inside one package, preferably on the same die.

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2024, 08:53:53 am
content: I thought I'd post a link to a thread offering some LM394s for free, in case the original poster hasn't seen it.https://www.eevblog.com/forum/projects/lm394s-free-to-a-good-home/

author: kimballa
author_rank: Contributor
timestamp: February 20, 2024, 04:40:05 pm
content: BCM847 for NPN, BCM857 for PNP are basically the only game in town I've found that's reliably stocked, guaranteed matching specs (delta-Vbe < 2mV), and available at about $0.50 per pair.Both are SOT-23-6. I've used them successfully in DIY audio synth applications.

author: kimballa
author_rank: Contributor
timestamp: February 20, 2024, 04:41:05 pm
content: PS make sure you get the BCM - M for matching. There's a separate unmatched NPN called BC847. Not the same.

author: prosper
author_rank: Regular Contributor
timestamp: February 21, 2024, 02:55:46 am
content: i have a curve tracer. hand matching transistors out of a bag isn't all that time consuming. i wonder how easily a curve tracer could be be constructed today with modern parts - you don't even need all the bells and whistles, or even a display; set it up to run a handful of measurements near your expected operating point on two parts at once, and light a led iif they're close enough. might be an interesting project

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 21, 2024, 05:05:53 am
content: Quote from: kimballa on February 20, 2024, 04:40:05 pmBCM8xx are 5% HFE matching, you can also get tighter HFE matching to 2% HFE and 2mVhttps://www.nexperia.com/products/bipolar-transistors/special-feature-transistors/matched-pair-transistors#/p=1,s=0,f=cf9523:0.98;0.98,c=,rpp=,fs=0,sc=,so=,es=

author: Limhes
author_rank: Contributor
timestamp: February 21, 2024, 05:49:04 am
content: I second the BCM8xx solution. These are the only reliably sourceable option imho, even with some pin-to-pin alternatives.I used them to build discrete Wilson current mirrors to bias a lateral PSD (2D photodiode, kind of). A visiting electronics engineer (an "oldie") was visibly impressed by me, a " youngster", building a discrete front-end in favor of the (legacy) implementation with 6 stacked (expensive and out of stock) voltage references and Frankenstein TIA.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 21, 2024, 08:38:51 am
content: Quote from: prosper on February 21, 2024, 02:55:46 amA limited parameter tester could be build relatively easy. For efficient matching it still makes sense to actually measure the relevant parameters and than after testing some 10 or 20 pieces select suitable pairs that are close together. For this one needs numbers, though no need to be super accurate. For just VBE matching the diode testfunction of a DMM can be good enough, as there is anyway the thermal effect.For hfe one may get away with the function included with some no so safe cheap DMMs.

author: David Hess
author_rank: Super Contributor
timestamp: February 21, 2024, 09:46:15 am
content: Quote from: twospoons on February 15, 2024, 03:59:52 amIt hardly takes any time, at least the way I do it. Usually I grade devices for Vbe or Vgs at a reasonable current, meaning every device is placed in a bins of 100 microvolts or 1 millivolt, and then thebirthday paradoxwill quickly result in multiple matched devices.Then I either clamp multiple devices to the same heat sink, or epoxy them together.If anything the trickiest part is that self heating during measurement causes the reading to shift.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 21, 2024, 10:12:53 am
content: For manually matching I would probably make a differential pair with sockets for the 2 transistors, and select the pairs with the best common mode input rejection. No matter how careful they are matched initially, the slightest temperature difference between the two transistors will affect the performance. Adding a common radiator for the individual transistors helps, but there will still be some thermal resistance that might keep the transistors at slightly different temperatures.The advantage with factory matched transistors is that they are in very close proximity to each other, often on the same die, which will keep them at a much closer running temperature. Even so, that will work for pairs only, while sometimes there is a need to match more than 2 transistors.Ideally will be to be able to make custom ICs.Don't know for others, but I'm a little disappointed. We still can not 3D print at home our own ICs after so many years. Don't want the finest sub nanometer tech, but something from 50+ years ago should be desktop technology today, one might expect.Rant aside, even inside the same IC, I've read there are situations where thermal pairing must be treated specially, i.e. precision opamps have a thermal axis of symmetry, where the input transistor are placed in such a way that the heat from the output stage/transistors will spread to the input transistors equally, to not ruin the matching. IIRC first introduced for uA725.Took a search to double check that, it was George Erdi:QuoteSource: page 61 of 970http://www.miedema.dyndns.org/co/2018/Op_Amp_Applications_Handbook-Walt-Jung_2005.pdfWell, not that I need any of such near perfect matching performance.

author: HalFoster
author_rank: Frequent Contributor
timestamp: February 21, 2024, 10:38:09 am
content: There are still several quad transistor packages made - of course there is the line from THAT as well as AD and others. Yes, somewhat more expensive than discrete but generally under $10 USD - and probably much cheaper in the long run with much better performance as matched items.

author: magic
author_rank: Super Contributor
timestamp: February 21, 2024, 12:50:14 pm
content: Quote from: RoGeorge on February 21, 2024, 10:12:53 amThe problem is not nanometers but chemistry. It was ugly 50 years ago, it is ugly today, it will stay ugly forever.You can't 3D print doped semiconductors.A few people managed to fab basic MOSFETs in home labs.

author: iMo
author_rank: Super Contributor
timestamp: February 21, 2024, 12:56:46 pm
content: This guy is doing DIY transistors for many years alreadyMany vids on the equipment in his basement as well..

author: magic
author_rank: Super Contributor
timestamp: February 21, 2024, 01:06:25 pm
content: I wonder howgoodbadhis Vgs matching is.

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2024, 01:53:29 pm
content: What about the CD4007UB for MOSFETS? I expect it won't be as well matched as specially designed matched pairs, but it's likely to be better than two discrete MOSFETs. There's also the slightly newer HEF4007UB, which might be better.https://assets.nexperia.com/documents/data-sheet/HEF4007UB.pdf

author: David Hess
author_rank: Super Contributor
timestamp: February 21, 2024, 02:34:05 pm
content: Quote from: RoGeorge on February 21, 2024, 10:12:53 amDifferential pairs can be further thermally balanced by adding resistors in series with the collectors to halve the collector voltages. Then when the pair is unbalanced, the power dissipation stays the same on both sides. High frequency performance is preserved by capacitively bypassing the resistors.QuoteMonolithic matching is not a panacea. Parasitic coupling between the transistors will spoil things like settling time and will spoil performance in high frequency applications, so there is still a place for matched dual parts which provide thermal isolation. In the past precision fast settling designs used either discrete or hybrid construction. Monolithic fast settling time parts do not compete and have relaxed accuracy from low open loop gain.

author: David Hess
author_rank: Super Contributor
timestamp: February 21, 2024, 02:37:05 pm
content: Quote from: magic on February 21, 2024, 12:50:14 pmBipolar parts, especially with an all NPN process, should be much easier. I remember one guy who was making tunnel diodes in his garage since they are easier yet because of high doping.

author: magic
author_rank: Super Contributor
timestamp: February 21, 2024, 04:14:21 pm
content: I have heard that silicon epitaxy is not easy at all (temperature, pressure, fun chemicals like silane) and without epitaxy you are limited to quite primitive discrete devices.

author: mawyatt
author_rank: Super Contributor
timestamp: February 21, 2024, 04:38:59 pm
content: Quote from: RoGeorge on February 21, 2024, 10:12:53 amEric's cross-coupled quad was a very valuable concept that everyone used, Fairchild really is the origin of all the greatest early semi folks!!At the IC level other things can creep in that even Erdi's quad can't eliminate. We utilized very complex thermal models for the SiGe BiCMOS processes we were involved with, these included not one but two non-linear device thermal time constants and took into account surrounding circuity and layout of such. These thermal models scaled non-linearly with device type, size, and layout orientation, even location of wire bonds had an effect as they became a thermal sink.In the end if one required extreme matching, it's always best to use differential techniques, Erdi's quad, symmetrical layout within and around the critical pair. Recall one integrated VCO design where we located a "matched pair" inside a large open center inductor where they would "see" an equal and matched thermal and electrical local environment.Lots of effort went into thermal modeling even at the device level, including thermal details inside the device, where even doping type, concentration and profiles have effects at the time.BTW your idea of using a high gain op-amp based diff amp front end for the DUT as the diff amp devices is likely the best means for precise matching., especially if one can reasonably match the desired electrical bias conditions. This is exactly what we did back in ~70 to check selected matched NPN pairs in TO-99 cans that National provided.Best,