Fool'n around with DSO & AWG - Page 1
Forum section: electronics / testgear

author: mawyatt
author_rank: Super Contributor
timestamp: September 17, 2022, 07:12:25 pm
content: Grabbed a 2N3904 from the junk pile and wondered if it was any good? Could have used a DMM or T7 Component Tester but that's no fun, so decided to see if the SDS2000X+ with an AWG could be easily "coached" into a Component Curve Tracer.Set the AWG (SDG2042X) Channel 1 to provide the Sweep Voltage using a Trapezoidal Waveform with a DC Offset so the waveform is ~unipolar, this goes to DSO Ch1. AWG Channel 2 was setup with a Rising Stair-step waveform for the bias stepping. Used a 100 ohm current sense resistor for DSO Ch2 in the DUT emitter and a 1Meg base bias resistor to the AWG Ch2. AWG Ch1 was connected to the DUT collector. Here's the results with scope set to XY mode, it's noisy and made no attempt to reduce noise. Result was 2N3904 is fine#88 is 2N3904 with Vertical scale of 20mv/100 ohms, or 200uV/div#91 is with higher collector sweep range#90 was using a custom HV amplifier (we developed awhile back to augment the AWG, details somewhere here on EEVblog) connected to AWG to sweep the voltage higher to show beginning 2N3904 collector breakdown, note horizontal (DSO Ch1) scale factor.Then we got a 3A 400V NPN and used a Juntek DPA1698 AWG Buffer Amp for more DUT current.#92 is 3A NPN with 10 ohm emitter current sense R, so scale is 200mv/10 ohms or 20ma/div#93 is with 1 ohm emitter resistor, scale is 200mv/1 or 200ma/divAnyway, this was a little fun play'n around this afternoon.Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: September 17, 2022, 08:28:53 pm
content: He, he, nice weekend proj: "Ad-hoc Curve Tracer!"To see the reverse breakdown, I've used once a step-up transformer connected straight to the AWG's output (all passive, no amplifier).P.S.Please always add a hand-scribbled schematic with the setup, or else only those who already know will understand.

author: mawyatt
author_rank: Super Contributor
timestamp: September 17, 2022, 09:12:08 pm
content: Good name!!Attached is the sketch and setup images.Best,

author: tautech
author_rank: Super Contributor
timestamp: September 17, 2022, 09:46:48 pm
content: Thanks for sharing this with us Mike.Can I ask if you have done this before with other DSO's or did that little voice inside your head tell ask you what happens if I do this ?

author: mawyatt
author_rank: Super Contributor
timestamp: September 17, 2022, 09:55:07 pm
content: Never tried this before with any DSO, back in our lab when I was working we had a proper Tektronix Curve Tracer, so no need to try.Here's another trace with a Power NMOS device (18A 200V), works equally well as it shouldEdit: And another of an IRF740 showing the NMOS Triode Region.Gotta love just how versatile these DSOs are, they aren't just an oscilloscope but a very good Analog Data Acquisition system with almost unlimited flexibility. As 2N3055 mentioned over on the new Rigol HD thread, the ADC is only part of the overall System, the rest of the Data Acquisition needs to been done well and Siglent has certainly demonstrated such to us with the SDS2000X+Best,

author: mawyatt
author_rank: Super Contributor
timestamp: September 17, 2022, 10:45:27 pm
content: Now here's a very interesting set of curves from way way back!! This is a 2N3904 operating upside down or reverse, with the emitter and collector exchanged. So Vce is now from the emitter which is positive to the collector, and Ic now flows into the emitter and out the collector toward ground thru the current sense resistor which is 100 ohms.Back in the very old days (60s) we utilized certain transistors upside down or reverse as analog switches because they had such a low saturation voltage when operated reverse.The current scale factor is 50mv/100 ohms, or 500ua/div, and note the first image the low breakdown ~5 volts of the emitter junction and the low saturation voltage is the second (scale is 100mv/div).Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: September 17, 2022, 10:54:10 pm
content: Quote from: mawyatt on September 17, 2022, 09:55:07 pmModern instruments are indeed great, not to say nowadays everything can be interfaced with a PC, then there's no limit for what they can do. For example, for MOSFETs and couple of amps range current, did once a curve tracer from the power supply alone, no generator and no oscilloscope, just that the RIGOL DP832 power supply was controlled by SCPI over LAN (LXI), then cobbled a few Python lines in a Jupyter Lab Notebook, and got this:https://www.eevblog.com/forum/testgear/rigol-dp832-power-supply-as-automated-curve-tracer/Quote from: mawyatt on September 17, 2022, 09:55:07 pmThinking about this as we speak, a good preamp+ADC, and DAC+amplifier, FPGA+RAM, all multichannel, high speed and attached to a PC, would make quite a universal EE instrument. Those blocks could be configured as DSO, DAQ, AWG, DMM, power supply, controlled load, whatever. Wonder why nobody does such a box.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 17, 2022, 11:04:57 pm
content: Quote from: mawyatt on September 17, 2022, 10:45:27 pmWhat!?!Gotta try that myself tomorrow (or today, 'cause it's 2AM here).

author: mawyatt
author_rank: Super Contributor
timestamp: September 17, 2022, 11:34:03 pm
content: Quote from: RoGeorge on September 17, 2022, 10:54:10 pmThat's great looking plot!!! A good PS or SMU is certainly an excellent method for creating a nice looking curve tracer. Very nice cobblingA while back we had thought of developing much of what you describe as a Component Curve Tracer, since good accurate ADCs and DACs are available, however not very good at coding and such, so abandoned the idea. Here's a list of the specs we were after.Fully self contained with no need for PC or anything else. would be designed around RPi with +12V DC input power.3 or 2 Terminal DevicesN and P Types+-30V LV Range @ 2A+-175V HV Range @ 0.1A+-15V Gate Drive+- 0.1A Base DriveXY DSO outputsPulsed Capable to limit heat build up in DUTDUT Thermal SensorThe device current would be sensed with a precision Transimpedance Type Amp which forces the test terminal to virtual zero volts. This is similar to high quality Lab type LCR meters. Also various DUT current ranges from 100na to 10 amps full scale.Anyway, with your skills this type of device should be achievable.Best,

author: ledtester
author_rank: Super Contributor
timestamp: September 18, 2022, 05:03:07 am
content: Quote from: RoGeorge on September 17, 2022, 10:54:10 pmGiven your extensive posting history I can't tell if you're being facetious or if you're referring to an Digilent Analog Discovery.https://digilent.com/reference/test-and-measurement/analog-discovery-2/start

author: MikeP
author_rank: Regular Contributor
timestamp: September 18, 2022, 07:08:55 am
content: For the purity of the experiment, current feedback should be eliminated. I'm talking about the emitter resistor. The entire test setup must be grounded at the emitter. Accordingly, the current signal from the resistor will appear in an inverted form.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 18, 2022, 10:53:00 am
content: Quote from: mawyatt on September 17, 2022, 07:12:25 pmInteresting setup, thanks for sharing!Can you point to the HV amplifier thread, somehow I can not find it.

author: mawyatt
author_rank: Super Contributor
timestamp: September 18, 2022, 12:17:55 pm
content: Quote from: MikeP on September 18, 2022, 07:08:55 amYes this would be the proper method, and why it's mentioned in the above (#8) if we were going to design and build a proper Curve Tracing Fixture using a Transimpedance amp which moves the current sense resistor into the feedback loop and forces the emitter node to virtual ground. Of course one also could move the current sense resistor above the collector and use a differential voltage probe across said resistor.Anyway, the kludge setup shown here was just for some fun playing aroundBest,

author: mawyatt
author_rank: Super Contributor
timestamp: September 18, 2022, 12:23:26 pm
content: Quote from: HighVoltage on September 18, 2022, 10:53:00 amSure, here's a couple that you might find interesting. The one we used is based upon the OPA462 HV Op-Amp.https://www.eevblog.com/forum/testgear/hv-buffer-amp-for-awg/msg3623953/#msg3623953https://www.eevblog.com/forum/testgear/cheap-diy-high-powervoltage-awg-buffer-amp/msg3449784/#msg3449784https://www.eevblog.com/forum/testgear/awg-buffer-amp/msg3368650/#msg3368650Best,

author: mawyatt
author_rank: Super Contributor
timestamp: September 18, 2022, 07:30:43 pm
content: Here's a few more interesting plots using this setup with just voltage sweeping the device.#99 is a 6.2V Zener at 1ma/div with 100 ohm sense R#100 is a 1N4733 Zener (5.1V)#101 is a 1N4799 Zener (24V)#102 is a 1N5817 SBD, note the low froward conduction voltage SBD are noted for#103 is a very interesting plot, note the zero axises are moved to the lower left corner for a better display. This is a reversed (exchanged collector and emitter) 2N3904 with base connected to ground thur a 100K. A 1K is used from the collector to ground for current sensing (500mv/1K or 500ua per div) for CH2 and 10K is to the emitter from the + sweeping voltage with the AWG feeding the mentioned HV amplifier. Scope CH1 is across the emitter to ground to show the DUT voltage.Note the negative incremental resistance (dV/dI) exhibited by the voltage across the reversed 2N3904 folding back occurring ~11V while the current is increasing, thus dV/dI is negative!! As the current continues to increase the negative resistance subsides and goes thru zero ~700ua and then become positive.Just to proof to ourselves we were actually "seeing" a negative resistance, we attached a 1uF Mylar capacitor from the emitter to ground and set the AWG sweep to produce ~13.3VDC across the DUT, which produces about 250ua current, right in the middle of the negative resistance range as shown in plot #103.#104 shows the classic relaxation oscillations created by the negative resistance reversed 2N3904.Anyway, hope some folks find this stuff interesting!!Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: September 18, 2022, 11:03:55 pm
content: This is too much fun already!You sure it's not illegal?A switch with zero AC resistance seems a very interesting component, is that exploited in practice?

author: mawyatt
author_rank: Super Contributor
timestamp: September 19, 2022, 12:18:33 am
content: Don't know if it's useful as a switch since the zero ohms would only be over a narrow bias current range. Just did a quick test where we injected a signal into the emitter of the 2N3904 at 1KHz 2Vpp thru a 100K resistor and 1uF decoupling capacitor. You can see the signal collapse as you slowly sweep thru the zero ohm region at ~11.9 VDC bias, and then expand as you pass thur. It's like sweeping a notch filter only in the bias domain!!Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: September 19, 2022, 09:01:50 pm
content: Quote from: mawyatt on September 17, 2022, 10:45:27 pmIs the BJT model critical for the reversed Vsat trick to work?Asking because in simulation it worked great, seeing reversed Vsat of less than 2mV, while in practice the reversed Vsat was about the same as the normal Vsat. Wanted to use the reversed transistor's low Vsat to switch on a discharging resistor for a 1.2V Ni-MH cell (discharge current in the range of 100mA) only to find out Vsat is about the same for either normal or reversed Vsat (70mV Vsat reversed, instead of 80mV Vsat normal).Tried with two transistor, both with B=430 normal, and with CE reversed one was showing B=3, the other B=12. The transistors type is SF128 D, video/RF NPN 600mW, TO-39 metal can. Will look for other medium power transistors to try, and will use soldered wires instead of alligators next time.Attaching the simulation for a generic NPN (not SF128) and the only datasheet I could find for SF128.How to choose the type of the transistors better for reversed mode?

author: mawyatt
author_rank: Super Contributor
timestamp: September 20, 2022, 01:30:01 am
content: A lot will depend on what parasitic resistances the transistor has, and how well the model takes care of these as well if it's even capable of accurate reverse behavior. When we utilized this way back, recall the switching type transistors behaved the best (have a higher doping level in the base/emitter) while reversed but can't remember the exact device type tho.Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: September 20, 2022, 07:49:14 am
content: Will test some switching transistors then, thank you.Just for the docs, found a brief class notes for the reversed transistors, has formulas for reversed Beta:http://web.mit.edu/6.012/www/SP07-L18.pdf

author: nctnico
author_rank: Super Contributor
timestamp: September 20, 2022, 07:54:31 am
content: Quote from: RoGeorge on September 19, 2022, 09:01:50 pmLikely the older transistors work better. A long time ago I played with an avalanche pulse generator. I found out that the modern transistors don't work well or not at all. The good old 2N3904 worked like a charm though. Seems to have to do with different production methods.

author: tautech
author_rank: Super Contributor
timestamp: September 20, 2022, 08:26:02 am
content: Yep as Nico says the old bipolar types particularly 2N2369 was famously used for the Jim Williams avalanche pulser.Dave did a vid on it years ago and for a while member free_electron was making kits however IMO todays Leo Bodnar pulser is a superior product.Some reading:https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/IIRC it was based on App note AN47 from Linear

author: HighVoltage
author_rank: Super Contributor
timestamp: September 20, 2022, 09:48:09 am
content: Quote from: tautech on September 20, 2022, 08:26:02 amYes, the fastest rise time I ever got out of the Jim Williams 2N2369 avalanche pulserwas around 400ps. The Leo Bodnar pulser gives faster than 50 ps rise time.The concept of the Jim Williams avalanche pulser is just amazing!

author: RoGeorge
author_rank: Super Contributor
timestamp: September 20, 2022, 11:28:17 am
content: The Vec saturation voltage in mV range is expected for reversed mode,reversedmeaning here that the CE terminals were swapped between them. It all works at voltages lower than 5V (lower than Vbe reverse breakdown). I don't see how the reversed mode BJT, and its expected very low Vsat, is related with the controlled avalanche breakdown from that pulse generator.If the pulse generator mention was only as a side note while recommending older transistors, then these SF128D tested in reversed mode happens to be old indeed. They are NOS found this weekend while digging in one of the scrap boxes I have from 20+ years ago, found together with some other NOS transistors and ICs from the same era, fabrication date probably during the 80s-90s era.

author: mawyatt
author_rank: Super Contributor
timestamp: September 20, 2022, 01:40:06 pm
content: The ones we used reversed way back in 60~70 were a fast pulse transistor, but can't remember the number!! Don't think it was the 2N2369 tho.BTW thanks for the MIT find, that's a great referenceBest,

author: Frex
author_rank: Regular Contributor
timestamp: September 20, 2022, 05:29:11 pm
content: Hi all,The fun thing about this controversy is that the first thingwe see on the top of the thread is a Keysight banner ...Frex

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 20, 2022, 07:44:24 pm
content: Quote from: mawyatt on September 17, 2022, 09:12:08 pmthanks my dear.Quote from: Frex on September 20, 2022, 05:29:11 pmthats the trap for young player.

author: mawyatt
author_rank: Super Contributor
timestamp: September 30, 2022, 09:37:33 pm
content: Per suggestion here's another thread related to the Curve Tracer DSO & AWG usage:https://www.eevblog.com/forum/projects/dso-awg-based-curve-tracer/Best,

author: tekguy
author_rank: Contributor
timestamp: October 01, 2022, 05:51:44 pm
content: What is an awg?,the only thing i know as awg is american wire gauge ?.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 01, 2022, 06:52:02 pm
content: Arbitrary Waveform Generator (AWG)Digital Storage Oscilloscope (DSO)

author: tautech
author_rank: Super Contributor
timestamp: October 01, 2022, 07:28:13 pm
content: Quote from: tekguy on October 01, 2022, 05:51:44 pmIn capitals means nothing other than an Arbitrary Waveform Generator better known to old farts as a FG but a AWG is many times more useful than an FG. Study of the first post or 2 indicates we need both Staircase and Ramp/Triangle waveforms, I may be wrong but I've never seen an FG that could do a Staircase.For this project a 2ch frequency source is required of which old school 2ch FG's are quite rare whereas 2ch AWG's are very common and for this usage perfectly suited.

author: mawyatt
author_rank: Super Contributor
timestamp: October 01, 2022, 08:33:46 pm
content: Quote from: tautech on October 01, 2022, 07:28:13 pmAnd the two waveforms (Ramp and Stairstep) need to be synchronized. One Ramp Sweep for each Stairstep, otherwise the curve plot will likely look very messy!!Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: October 01, 2022, 08:44:47 pm
content: And for those who don't have an AWG, for curve tracing the AWG can be substituted with this:https://www.qsl.net/w2aew/youtube/curvetracer.pdfAnd for those who don't have a DSO either, any analog oscilloscope with XY mode will work. In fact, old analog oscilloscopes are working much better in XY mode than a usual DSO.

author: tekguy
author_rank: Contributor
timestamp: October 01, 2022, 09:30:42 pm
content: very true,i have a tek 465 and a rigol dso 50mhz 1GSa/s the 465 knocks spots off of the rigol with an octopuss in xy mode,works but only just!.

author: tautech
author_rank: Super Contributor
timestamp: October 01, 2022, 10:14:57 pm
content: Quote from: tekguy on October 01, 2022, 09:30:42 pmPlease in a EE forum make the effort to have units specified correctly !Did you mean MHz not mHz ?

author: Sensorcat
author_rank: Regular Contributor
timestamp: September 24, 2024, 05:46:59 pm
content: When I discovered this thread, I thought this "Ad-hoc Curve Tracer" is great for me and everyone who does not like to have another box getting dusty while waiting for the next time it is needed. Since I do not have an analog scope, the only disadvantage I see is the not-so-impressive performance of many DSOs, including mine, in XY mode. But it appeared to me that XY mode is not necessary for a curve tracer, because it has a linear function of voltage on one axis, and the usual YT mode has a linear function of time.So I set up the circuit and my AWG as presented by @mawyatt above and played around with instrument settings on my Rigol MSO5000. For the sake of completeness, the transistor is a BC238A. What I got is shown in image 'curve_tracer_YT'.Compare this to using XY mode, with and without HighRes activated, images 'curve_tracer_XY_HighRes' and 'curve_tracer_XY_Normal'. HighRes does not perform well (especially in XY mode), a known flaw of the MSO5000, but somewhat reduces the trace width, while producing additional artifacts in XY. I started with YT mode and later did not change channels, so the XY images are not in the commen orientation.Clearly, YT mode produces a better result, a cleaner image without dots all over the screen. Since it does not depend on the DSOs XY performance, it is expected that using YT mode improves the result on many DSOs. Another advantage of YT mode is that the whole screen area can be used. It would be easy to expand the traces to hide the parts left and right of the actual curve tracer plot, to match the image that XY mode provides. I thought I leave it as it is, because this way it shows what's going on.The scope settings that required attention are:In Display menu, 'Dots' instead of 'Vectors' to reduce line widthIn Display menu, 'Persistance' = 5s, 'Intensity' = 100%, 'ColorGrade' = OFF, 'Waveform Freeze' = ON. These settings make all lines appear similar, regardless of the plotting sequence, and all lines stay on screen if the acquisition is stopped, for instance to take a screenshot.In Acquisition menu, 'HighRes' = ON, 'Mem Depth' = 10k

author: Aldo22
author_rank: Super Contributor
timestamp: March 25, 2025, 04:28:04 pm
content: Hi!Thanks for the example.I tried to reproduce that today with my humble equipment.Would you say from the screenshots that this is how it works, or is there something missing?I'm not sure if I'm interpreting this correctly.

author: mawyatt
author_rank: Super Contributor
timestamp: March 25, 2025, 04:36:10 pm
content: Looks as you've got things setup properly and result looks goodBest

author: Aldo22
author_rank: Super Contributor
timestamp: March 25, 2025, 05:46:17 pm
content: Quote from: mawyatt on March 25, 2025, 04:36:10 pmThank you, I'm happy now!I was a bit lost for a while.I only have the FY3200s and the DSO2000.At first I thought it might not work with this equipment.I had to teach the FY3200s the ramp first, as this wave form is not built in.Then everything has to be right with the frequencies, amplitudes and offset. The resistors must also fit and then the oscilloscope settings.At some point it looked halfway right, but I wasn't quite sure.But it all matches the thread title: “Fool'n around with DSO & AWG”.

author: mawyatt
author_rank: Super Contributor
timestamp: June 06, 2025, 04:06:02 pm
content: Quote from: mawyatt on September 18, 2022, 07:30:43 pmDecided to use this Reversed 2N3904 Base-Emitter Breakdown Negative Resistance Region to create a narrow pulse similar to the Avalanche Collector Emitter Breakdown method commonly used (see famous LT App Note 47-D) for fast pulse generation.Installed a 50Ω resistor in the "Collector" of the Inverted 2N3904 to ground, while the "Emitter" is returned to +14 Volt Supply thru a 100KΩ Resistor and the Base is open. A 10nF Cap from the "Emitter" to ground. With this setup when the Emitter-Base Junction begins to breakdown, the current flows thru the Base-Collector forward biased Junction to ground.Cyan trace is the AC coupled DSO across the "Emitter", and the Magenta trace is across the "Collector" 50Ω resistor.Works OK but not nearly as fast as the C-E Avalanche Breakdown method, but doesn't require a ~100V supply eitherAnyway, another fun use with the old 2N3904Best