PRP1 - Low cost 2GHz power rail probe - Page 1
Forum section: electronics / testgear

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 10:00:25 am
content: I'm calling this PRP1. It's a power rail probe, that is oscilloscope agnostic and low cost.I've started working on this because normal power rail probes cost around 10 times as much as entry level oscilloscopes. I hope to change that with this probe.It's still very much in development, and I release some info about it, hoping to organize a group buy.Below is an image of the first 2 working prototype. I've some promising measurements from the prototypes already.Specifications:Max voltage offset: ±24VDC Input impedance: 50kΩHigh frequency input impedance: 50 OhmSignal attenuation of 1.3:1Transfer function within 1dB to 2GHzEstimated noise: 42µVp-pRMS to 20MHzActive signal range: +/-350mvCourse - Fine adjustmentUSB Type C 5V power input - run it from your oscilloscope directlySMA input and output. SMA to BNC cable to connect to oscilloscopeTypical power consumption of 20mA(Specifications are yet to be verified by independent third party.)

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 10:02:21 am
content: Example probing setup. PRP1 measuring power supply ripple of an ESP32 board with a Siglent oscilloscope, using external 50 Ohm termination.Dual probing power supply ripple with PRP1 and standard oscilloscope probes. Siglent oscilloscopeCH2 is standard oscilloscope probe, CH3 is PRP1Noise level of PRP1CH2 is input terminated with 50 Ohm, CH3 is PRP1Dual probing power supply ripple with PRP1 and standard oscilloscope probes. Keysight MSOX 1 GHz oscilloscopeCH1 is standard oscilloscope probe, CH3 is PRP1. Note the lower noise levels of the PRP1

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 10:03:34 am
content: Low frequency transfer function:Note this measures up to 10MHz, which includes the low frequency crossover point of the probe.High frequency transfer function:Some TODO, to declare the status of the project:Some trivial changes to the PCB, that are patched on the prototypePrototype only reached 23.6V, needs a slight adjustment to the referencesIf possible, bring U6 underneath the internal shielding canGoing from 2 PCB solution (potentiometers) and wiring to one PCB2 Potentiometers too big to fit on front panel, second potentiometer should be fine adjust typeMaybe go from end-launch SMA to TH, to bring the connector closer to the middle of the enclosure. On the other hand it's ascetic only, and it would reduce performance.Drawings of enclosure to outsource the cutouts. So the end product doesn't look like I hacked some holes on it with a drill and some files. I've contact with the manufacturerQuality SMA to BNC cable is needed. I've found half the time the cable, and the BNC connector made 4x the noise than the PRP1

author: tautech
author_rank: Super Contributor
timestamp: August 23, 2024, 10:05:33 am
content: Nice, OP image needs resizing....good you've done it.Dunno what it is but we have one coming soon too, a 4 GHz version.Wanna know the specs of what you're up against ?

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 10:49:12 am
content: Quote from: tautech on August 23, 2024, 10:05:33 amThanks. I'm eager to find out.There are many benefits of using a factory built probe, it tells you on the screen what the voltage you are looking at, and with the active probe it's a better interface.Still, I hope people with low-end scopes or budget will be able to use a probe like this.

author: tautech
author_rank: Super Contributor
timestamp: August 23, 2024, 11:24:46 am
content: Quote from: tszaboo on August 23, 2024, 10:49:12 amSnippet attached.To be released next month.

author: jonpaul
author_rank: Super Contributor
timestamp: August 23, 2024, 12:42:28 pm
content: overload, transient protection?j

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 01:17:59 pm
content: Quote from: jonpaul on August 23, 2024, 12:42:28 pmThe parts are rated to 50V. Right now I don't have any output clamping, nor do I have capabilities to test surge.In the commercial designs they have output clamps, diodes, or double diodes. I'm still searching for the right part.I'd like to point out that even commercial probes are very scarce in info when it comes to protection.

author: Neganur
author_rank: Unknown
timestamp: August 23, 2024, 01:38:42 pm
content: Guessing the keysight probe was source to your inspiration?

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 01:59:53 pm
content: Quote from: Neganur on August 23, 2024, 01:38:42 pmInspiration came from:Keysight probe that I used before.Lecroy article " Buld your own power rail probe"https://www.signalintegrityjournal.com/blogs/8-for-good-measure/post/1898-build-your-own-low-cost-power-rail-probeCircuit stellar article by Andrew Levidohttps://circuitcellar.com/research-design-hub/projects/building-a-power-rail-probe/My schematic differs from this published one quite a lot, even though it might have started like it.Honestly, I wanted to build one for a while, and I picked it up because a GPS receiver was having power supply issues, and I had trouble measuring it.

author: JPortici
author_rank: Super Contributor
timestamp: August 23, 2024, 03:47:10 pm
content: Quote from: tszaboo on August 23, 2024, 10:49:12 amand one may wonder if there were APIs for the probe interface. Maybe siglent would be prone to provide a generic class of devices (I2C device id = 0xNN means power line probe, probe reports calibration factors in such format and responds to command in such other format)Ah, that would be indeed wonderful.Now back to lurking

author: nctnico
author_rank: Super Contributor
timestamp: August 23, 2024, 04:08:11 pm
content: Why not use a push-button electronic potmeter? I have been tinkering with the idea to add an offset to my HF differential probe and I drifted towards using an electronic potmeter. The advantage is having less noise (no wiper noise), a fine and more stable adjustment and no mechanical components.

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 04:56:07 pm
content: Quote from: JPortici on August 23, 2024, 03:47:10 pmFrom what I've seen, everyone keeps their probe interface locked down, probably even with serial numbers. The profit margin on active probes is a magnitude more than the scope itself, it's what makes the money.Quote from: nctnico on August 23, 2024, 04:08:11 pmI did consider that. I think the potentiometer is the noisiest part in the design (and sometimes the BNC connector). At least my ten turns trimmer pot was definitely making more noise than these Alps potentiometers. And it's done with that in the existing probes. For now I've shelved the idea, because I like the idea of having a product with no programmable parts.

author: nctnico
author_rank: Super Contributor
timestamp: August 23, 2024, 05:13:48 pm
content: There are up/down button potmeter chips which don't require any programming / software. Just hook up some buttons to pins and off you go.

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 05:45:05 pm
content: Quote from: nctnico on August 23, 2024, 05:13:48 pmI made a quick search and for example the MAX5450 would be suitable. It's 256 tap, that would bring the resolution of nulling to 180mV. So at least two would be needed.So browsing through the datasheets of these, you would need to press the up/down button 256 times to swipe across the range. I don't think it would be a good user experience.I also recall using some AD digipots, and they had quite bad tempco. These seem fine though from that point of view.

author: nctnico
author_rank: Super Contributor
timestamp: August 23, 2024, 06:17:43 pm
content: Quote from: tszaboo on August 23, 2024, 05:45:05 pmYou still have the offset control of the DSO itself so 256 taps would be overkill. 64 would be more than enough. Also, do you really need a 24V range? It would make more sense to have a 4V and 24V range which then translates into a 64 tap digital potmeter having plenty of resolution either way.

author: temperance
author_rank: Super Contributor
timestamp: August 23, 2024, 08:54:27 pm
content: QuoteI don't know what your schematic looks like but I assume you are just injecting an off-set into some amplifier input. Adding a filter might work. (but not with X7R capacitors) The circuit cellar schematic has a mistake in the schematic. The filter cut-off varies with the pot setting from no filter to some filter when the pot is adjusted to the center position.I prefer pot's over push buttons. Faster and less fiddling.Is there a reason why the front and back are made of aluminum? You could use FR4 and no extra manufacturing steps would be required.Edit: the Circuit cellar schematic might have more problems. It is meant to be powered from alkaline AA cells. Some battery chemistries show some ultra low frequency noise where the voltage changes all of a sudden 50...150 mV or even more for some lithium batteries. Those transient lasts from several seconds up to hours.

author: nctnico
author_rank: Super Contributor
timestamp: August 23, 2024, 09:11:24 pm
content: Quote from: temperance on August 23, 2024, 08:54:27 pmI get that, but long term potmeters tend to wear. Back when I was designing audio gear, I always filtered a potmeter to provide a DC level to a chip which did the actual control work (like changing the volume). In this case a potmeter would need a filter + buffer in order to get rid of nasty potmeter effects. But you can still get a slow wandering DC offset.

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 09:13:52 pm
content: Quote from: temperance on August 23, 2024, 08:54:27 pmI have to agree, pot is also my preference. There are a few issues with that circuit, that make it less than optimal. For example your offset voltage constantly changes as your battery discharges.I was using a 10 turns trimpot to bring up the circuit and test it. They were creating strange low frequency drift. I have to assume, that pushing the plastic housing of the trimpot introduces stress that will upset uV level signals. The time constant was seconds, no amount of capacitors will filter that. With these potentiometers it works much better.

author: tszaboo
author_rank: Super Contributor
timestamp: August 23, 2024, 09:30:35 pm
content: Quote from: nctnico on August 23, 2024, 06:17:43 pmWith +/- 24V that the probe can offset out, and +/-500mV, you can only ever investigate 1V around the setpoint with the probe. You need to bring the output signal of the PRP1 close to 0 otherwise any ripple could be clipped. With 48V/64 tap, the resolution is only 0.75V.It's also worth noting that while you sweep the offset voltage range, nothing happens on the oscilloscope. If your potentiometer is set to 0V compensation, and the signal is 20V, the pot needs to be turned all the way to 19.5V before the signal moves. You can do this with a fraction of a second with a pot, but with a digipot, it's pressing buttons and nothing happens. Not a very nice user experience.

author: temperance
author_rank: Super Contributor
timestamp: August 23, 2024, 09:53:39 pm
content: QuoteInteresting observation. But probably hard to avoid as the contacts must settle after tweaking. But some ten turn pot's are better than others.One of the better pot's around:https://www.bourns.com/products/potentiometers/industrial-panel-controls/product/3310https://www.bourns.com/products/potentiometers/industrial-panel-controls/product/91-95Those are used in pro audio equipment where those pot's are exposed to extreme vibration. (like next to stack of subs.)But of course that doesn't say anything about the effect you've noticed.I have some of those laying around (10K linear). Now I'm curious...

author: temperance
author_rank: Super Contributor
timestamp: August 23, 2024, 10:15:26 pm
content: Data for the 9195 attached.That's a 5K pot.DMM-5 Run 4 2020-08-06T15.00.35.xlsx(440.12 kB - downloaded 55 times.)

author: temperance
author_rank: Super Contributor
timestamp: August 23, 2024, 10:27:11 pm
content: I had an other fancy pot in my collection. Brand new.Vishay PRV6Edit: the remainder are some low cost pot's not worth testing.

author: Neganur
author_rank: Unknown
timestamp: August 23, 2024, 10:31:51 pm
content: 👍 nice

author: hpw
author_rank: Frequent Contributor
timestamp: August 24, 2024, 12:25:05 pm
content: Quote from: tszaboo on August 23, 2024, 10:00:25 amI did some early experiments as using an LNA (about 20dB gain) with 2 * +/- 9V batteries to measure the power ripple on various digital ADC/DAC. Differential, as to use similar PIN header connections as LeCroy AP034 differential probe.It started wit the differential AD8129 OPAMP with capacitors coupled and alike Pin header connections, this means no DC support but with higher load.While on ADC/DAC VRef is a critical on low PN frequencies as low as 10mHz. In addition the ripple on ADC/DAC digital or analog part. The ripple tells you much what is on the chip going on (or not should be drawing in any case).The GND current with unknown current on DUT & LNA & DSO must be avoided.The critical goes than on high RF frequencies as the CMRR of the LNA amplifier will go down the hill.Only MISIC show nice CMRR but never checked how they really performs. The 1GHz as for -3dB down really about 600MHz.At the end it shows about 3 different LNA devices required as:- 0.0xx mHz to 100Hz (large input capacitors required)- 10Hz to view xxMHz as for the average use- xxxHz to RF a 1GHz with good CMRR required as the beef test with high ADC/DAC with 100MHz locks.Important to check with asymmetric connections on a DSO with good ADC resolutions as SDS2000 Plus 10Bits and input probe scaling for the LNA.The FFT size & FFT Window is by this DSO not optimal for all ranges (SDS7000 as with 32M samples at best).Later on a nice rtHz plot is an must do as BIN export and import with an FFT Analyzer.Some parallel entries found on diyaudio Equipment forum

author: tszaboo
author_rank: Super Contributor
timestamp: August 24, 2024, 07:26:37 pm
content: Quote from: temperance on August 23, 2024, 10:27:11 pmI quickly measured the trimpot that I removed. The 4th Digit on the 6.5 digit DMM was already jumping around.It kept on doing this evenMeasured an ordinary 0805 resistor, only the last digit moves. I also measured the pot that I wish to use in the final design. I noticed some effect, that after moing, it was drifting for more than a minute to the same direction. I set it up to ~10KOhm, and it would drift to 9981 Ohm I'm not sure if this is a heating up effect of the DMM, or something mechanical. Anyway after the drifting, only the last digit changes again, so it's 100 times less noisy than the trimpot. Unfortunately my 34401A doesn't do ratiometric measurement.So rather than giving up, I placed the pot in the fridge for about 10 minutes, and after taking it out, connected the DMM across the two end terminals. It went from 11560 Ohm to 11146 Ohm, Unfortunately Alps doesn't specify the tempco of their pots. But I use it in ratiometric mode, and wiper current is minimal, so there shouldn't be any drift and low frequency noise happening.And here is the interesting part: I grabbed another 10 turns trimpot from the same type. And it didn't have drift and noise.So I have to assume handling it there is a failure mode when it becomes noisy.To be not only off topic, I made quite a bit of progress on the probe. Found the issue of the full scale 24V problem, added ESD protection and ferrites to the USB line. In my investigation, the USB outputs of scopes didn't always play nice with the probe, they were injection noise, now it's not measurable on the scope I have.

author: temperance
author_rank: Super Contributor
timestamp: August 24, 2024, 09:26:42 pm
content: The pot drift/stability might have something to do with the track lubricant which lifts up the wiper ever so slightly while turning the pot. The RPV6 pot I tested is pretty expensive but worse than the 91-95. But the RPV6 pot is meant as a position sensing pot and probably contains more lubricant.I'm interested in such a probe. My last design containing a 2.4 GHz RF soc went trough RED testing with a very small margin for spurious emission. (probably caused by noise from the fly back power supply finding it's way into the PLL)I was thinking this topic would be gaining more attention.

author: tszaboo
author_rank: Super Contributor
timestamp: August 26, 2024, 07:50:12 am
content: Quote from: temperance on August 23, 2024, 08:54:27 pmThese two prototypes were (quite badly) modified by me with a drill and some sawing and filing.I was also waiting for the supplier to give me a quote for the modifications. It's not too bad, but I think I'll go with FR4 end plates for the first batch. I'll don't want to end up in a situation where the silkscreen is bad, and I have to reorder the housings.Some more measurements!This is the USB ripple when the PRP1 proto 2 is connected to the USB port. This is the 5V voltage directly from the USB.The voltage is measured with the other PRP1!After manual modifications to the input circuit:And the output of LDO on the board:As you can see the PRP1 was capable to measure this voltage ripple.The actual modifications reduced the ripple from 52mV peak to peak to 3mV. The rest is handled by extra ferrite beads, and the PSRR of the Opamps. The ripple there is on the output of the LDO is barely 600uV, and they have more than 30dB PSRR at these frequencies. The noise is not visible on the output

author: tszaboo
author_rank: Super Contributor
timestamp: August 27, 2024, 04:20:51 pm
content: Another day spent well. I've made quite a bit of progress, schematics is complete I think. I was focusing a lot on the coarse-fine adjustment, improving the linearity of the two potentiometers. The fine should have about the range to be able to change a signal in the active range now, so the coarse only needs to get the signal in view.I also spent time on the mechanical design, pictures are below. Instead of 2 wire assembly and 2 PCBAs it's now 1 PCB. Added an LED indicator. And spent 4 hours staring at potentiometer datasheets trying to figure out how to get the right one, then settling for something close to it.With this I'm off to BOM setup.

author: tszaboo
author_rank: Super Contributor
timestamp: August 30, 2024, 05:46:19 pm
content: I'm ready with everything to order the next prototype.I'm only waiting for some samples from TI to test out some more parts, just making sure that the probe schematic is optimal.Also I'm still waiting for some Coax cables, because RG316 with low quality connectors is not a good choice for the connection between the scpe and the probe.I dare to ask: Who is interested in getting one of these?Price 250 EUR + Shipping + paypal feesContents:PRP1SMA-BNC coax cable 0.8m for connecting scope (TBD likely RG142 or LMR240)SMA-UFL coax cable for connecting DUTSMA-pigtail coax cable for connecting DUTSMA-2.54mm square header coax cable for connecting DUTUSB cableOptionally P57 terminator (OK performance up to 200 MHz)I'm asking because there isn't a lot of price difference between ordering 2 or a few.

author: Calvin
author_rank: Regular Contributor
timestamp: September 01, 2024, 08:51:18 am
content: Hi,triggered by Your thread I quickly built a probe based on the circuit suggested by Tommi Otsavaara in his thesis "1 GHz Power Rail Probe".Seemingly he orientated on the Keysight N7020 probe that Sharia kindly dared to open up for usThe major differences to the Levido DIY-probe seems the higher output resistor of the LF-path of 590R which requires the second inverting stage to have a gain of -11.8, and the increased Offset range of up to 50VI had some OP270 lying around, which is a low en-noise dual OP27, which in simulation results in very nice low noise, but it´s decompensated and faster brother OP37 would be better suited to the second inverter gain stage.In the Levido probe where the second inverter is just a buffer with a gain of -1 the OP27 may get problems due to the required higher load currents.As alternatives TI lists some ´Soundplus audio-OPAs´ like the OPA1655/1656 with lownoise, sufficient GBW and high current outputs.If higher supply lines are possible the JFET-Input OPA827 appears interesting.Due to the overall high offset-gain of 118 the Otsavaara probe´s offset-setting becomes critically sensitive and rather requires multiturn-potis even though potis are used for coarse and fine tuning already.Another point is the lowpass filtering of the LF-path.The Otsavaara relies on simple RC-Filtering, which in this case leads to a shelving-filter character.In simulation this adds ~0.3dB of output signal level to the HF-path.The Levido probe on the other hand utilizes a RLC-filter that follows a LP-filter curve much closer, hence attenuates the LF-path alot better.@tszabooincreasing the Offset range from +-24V to +-50V or even more (R&S claims up to 60V) seems easy ... just a bit of shuffling values of the Potis and the offset-input resistor.Do You plan on offering a probe with higher offset range also?regardsCalvin

author: tszaboo
author_rank: Super Contributor
timestamp: September 01, 2024, 10:46:42 am
content: Quote from: Calvin on September 01, 2024, 08:51:18 amHi Calvin. I didn't see this thesis before, it's quite interesting.The circuits looking like the N7020 probe: There is an expectation on how the probe is supposed to work, if you deviate from it it would work differently. When taking measurements, the probe should be "transparent" meaning that it shouldn't show any behavior which makes you doubt :whether it's the DUT or your test setup is making certain outcomes. Wat I'm trying to say there is only so many ways this circuit can be built, if you deviate from it, it's a different probe.The thesis is quite ambitious for a BSC. I run into the same issue, a semester is not enough to design a board build it test it, but more importantly to document it. Because you get your grade based on the documentation.His circuit is a good effort on the analog path. His power supply is very noisy, these DC-DC modules can easily have 100mV ripple on the output. When you measure some high voltage, the potmeter is set to high, you would be measuring all the noise and ripple coming from that DC-DC, amplified. Even though he has a RC filter with an electrolytic cap. I don't think he built the power supply, probably used a bench power supply.Not to diminish his efforts for a BSC thesis this is very good.I don't think I would want to offer it with a higher voltage for now. Going for 48V would mean that I need to comply with the Low Voltage Directive, that I'm not willing to do now. If you are interested, I could accidentallysend you a probe that has it's resistor replaced, and it could measure higher voltages. It would also have higher noise levels.

author: temperance
author_rank: Super Contributor
timestamp: September 01, 2024, 02:02:48 pm
content: I saw this thesis. What I don't understand is all the fuzz about the coupling capacitor on page 23. The thesis also blames R&S for not plotting such data on page 11.On the plot shown on page 23 is a reference to a GRM188R72A104KA35 capacitor which is a X7R capacitor. This cap must be an NP0 or C0G type. His supervisors should have caught that.

author: Neganur
author_rank: Unknown
timestamp: September 02, 2024, 11:41:12 am
content: Quote from: temperance on September 01, 2024, 02:02:48 pmIt's "just" a B.Eng thesis. The supervisors do not typically pay attention so detailed on that level (sorry, Heikki). I would have slapped his wrist for not labeling the y-axis thoughPS: 1206, 100nF, 100V C0G/NP0 from Kemet is pretty darn expensive on Digikey. ~10 EUR for one. Maybe that was a money choice rather than a design choice.

author: temperance
author_rank: Super Contributor
timestamp: September 02, 2024, 03:48:49 pm
content: QuoteI've seen different prices some time ago on the mouser website. Let's see.Some 100 V C0G capacitors in 1206 can be had for less than €1. 200...250 V versions in 1206 are available for less than €2. Both in single quantity.

author: Neganur
author_rank: Unknown
timestamp: September 03, 2024, 09:18:31 am
content: oh right, I filtered for 1% tolerance - my bad. 2% and 5% are less than one Euro. good point

author: tszaboo
author_rank: Super Contributor
timestamp: September 03, 2024, 04:26:20 pm
content: And now something different.I'm exploring the possibilities of making a browser for the PRP1. This is a DIY solution, example of a commercial part:https://nl.rs-online.com/web/p/oscilloscope-probe-accessories/1444395It's made out of a 100MHz low end oscilloscope probe, it's internals were gutted and replaced with rigid coax. And glue.Not pretty, but I measured <1.5 VSRW up to 2 GHz with it. It's a bit of work to put together, the probe was glued.

author: temperance
author_rank: Super Contributor
timestamp: September 03, 2024, 04:52:03 pm
content: Quote2K6 pour une pièce de résistance... Did they hire an Audiofool to develop this cable?For me an SMA to open end cable will do. They cost nearly nothing.

author: Neganur
author_rank: Unknown
timestamp: September 04, 2024, 11:07:11 am
content: The Keysight SMA-SMA cable for the power rail is similarly expensive. At least with the Lecroy cable, you're also getting a special directional resistive browser head. At the end of the day though, it's the low quantity sold that sets the price.

author: Neganur
author_rank: Unknown
timestamp: September 04, 2024, 11:10:18 am
content: Quote from: tszaboo on August 30, 2024, 05:46:19 pmI'd pledge 100 for just the populated PCB, no need for cables or enclosure.

author: tszaboo
author_rank: Super Contributor
timestamp: September 04, 2024, 06:50:12 pm
content: Quote from: Neganur on September 04, 2024, 11:10:18 amI'm not planning on selling this with a discount.What I can offer is a free unit, in exchange for writing a review here, and verifying the performance of the probe.I think you have the test equipment to do that?

author: Martin72
author_rank: Super Contributor
timestamp: September 04, 2024, 08:42:27 pm
content: QuoteHow “deep” should the review be, in your opinion?

author: tszaboo
author_rank: Super Contributor
timestamp: September 05, 2024, 07:35:24 am
content: Quote from: Martin72 on September 04, 2024, 08:42:27 pmI'm not trying to entrap you with a lengthy homework.I only want someone competent to verify my claims to the specifications, to avoid making a mistake and disappointing people. RMAs.Spend however much time on the review you think a free probe is worth. It's a gentlemen's agreement anyway.

author: tszaboo
author_rank: Super Contributor
timestamp: September 06, 2024, 03:25:07 pm
content: PCBs, PCBAs and Enclosure ordered. I've requested quotations for the cables.Next thing is packaging. And instruction manual.

author: nctnico
author_rank: Super Contributor
timestamp: September 06, 2024, 03:56:53 pm
content: Quote from: tszaboo on September 04, 2024, 06:50:12 pmBefore anything, I think it is a good idea to figure out what kind of industry standard testing method exists for these kind of probes so specifications / test results can be compared with other probes.

author: tszaboo
author_rank: Super Contributor
timestamp: September 06, 2024, 04:20:35 pm
content: Quote from: nctnico on September 06, 2024, 03:56:53 pmI agree, I was going to put all that documentation on Github, including my test setups and results. And instruction manual.There is a performance verification guide in the instruction manual of a Tek probe:https://download.tek.com/manual/TPR1000-and-TPR4000-User-Manual-077154200.pdfFrom page 26. It gives a good baseline on what to measure. I found because of the changing input resistance of the probe (which is the whole point of it) measuring it was quite challenging. The high frequency verification seems to be just sweeping it with a VNA and finding the -3dB point. Which seems to be above 2 GHz in my case, but I still want to sweep the final design with a higher quality VNA before calling it faster. Using a SMA calibration standard on the probe's output. With a scope it's slower anyway, with a 50 Ohm adapter + regular scope input, I think it's limited to about 200 MHz. With a 50 Ohm input scope it should reach the scope's nameplate speed.

author: tautech
author_rank: Super Contributor
timestamp: September 10, 2024, 08:41:51 am
content: Quote from: tszaboo on August 23, 2024, 10:49:12 amComplete specs available now:https://int.siglent.com/u_file/images/24_09_10/SAP4000P_UserManual_EN01A.pdfYours will be a much lower cost version......

author: tszaboo
author_rank: Super Contributor
timestamp: September 10, 2024, 02:13:39 pm
content: Quote from: tautech on September 10, 2024, 08:41:51 amLooks like a very nice bit of kit.Any of these probes, especially the "low speed probe browser" would be an excellent accessory for my design.The high speed browser is an interesting design, I wonder if we can learn something from it's construction.BTW"5.3 Pigtail Cable Welding" - you might want to correct this it's a very obvious translation mistake from Mandarin.

author: tszaboo
author_rank: Super Contributor
timestamp: September 17, 2024, 11:02:49 am
content: I got a package, it was the assembled board of the PRP1.So I quickly went ahead and put the probe together.It went through a few tests, and the noise and +24V and -24V cancellation worked on the probe.SWR was also <1.5 below 2.5GHz. Crossover frequency showed a small bump, which was still within 0.25dB, or 3% gain error, which is quite acceptable. I only had these for about an hour now. Next few days, I document my testing method and results.USB port is a bit deep, but all the cables I tested worked.

author: nctnico
author_rank: Super Contributor
timestamp: September 17, 2024, 03:12:51 pm
content: USB-C sockets come in different lengths / depths. So as long as the plug is long enough for your design, it should work.Side note: I have come across USB-C sockets which where too long for any plug to mate. I had to grid a few mm away those.

author: tszaboo
author_rank: Super Contributor
timestamp: September 20, 2024, 12:22:42 pm
content: OK, so I've been working on documenting my test setup for the verification of the design specifications.I've already placed some test results of these tests here, and plan to release all orderly on Github.It's a total of 12 measurements with their own setup. I've the text here, with pictures of the setup, or a HTML collated.I'm open to discuss the test setups, let me know if you think I'm doing something wrong or you know of a better way.Text is in markdown, the HTML is nicer, but not supported as attachment, so I have it as PDF.Code:# Measurements done on the PRP1 Power rail probeThis documents lists all the measurements that are done on the PRP1 for design characterisation.\The measurements were done on TBD (at least two) separate units, results are published in folders## 1) Bode plot 10MHzVerifies the gain errors across the frequency span\!(1.png)\Equipment used:* Siglent SDS804X HD Oscilloscope* Siglent SDG1032X HD GeneratorSettings:* 10Hz to 10MHz* 121 point* 100mV peak to peak* 0V offset* Frequency mode: Linear* DUT input CH1* DUT output CH3* Load 50 OhmPass criteria: 1dB maximum deviation between minimum and maximum of the gain plotNote: Crossover frequency is ~ 100 KHz\Note: 1.3:1 is 0.77 or -2dB## 2) AC gain @ 10 MHzVerifies the 1.3:1 probe attenuation\!(246.png)\Equipment used:* Siglent SDS804X HD Oscilloscope* Siglent SDG1032X HD GeneratorSettings on generator:* 10MHz sine wave* 100mV peak to peak* 0V offset* Load 50 OhmPass criteria: 5% maximum deviation between RMS and Peak to peak value of CH1 and CH3\## 3) Noise measurement 20MHz BW 12 bit ScopeVerifies the noise figure of the PRP1\!(31112.png)\Settings:* PRP1 zeroed-out* PRP1 powered by lab linear power supply* PRP1 input shorted by SMA shoring plug or 50Ohm load* 2 mV/div on CH1 and CH3* 1 ms/div time scale* 20MHz bandwidth limitPass criteria:$\ Noise = sqrt{CH3^2 - CH1^2) < 50uV$## 4) DC gainVerifies the 1.3:1 probe attenuation on DC\!(246.png)\Equipment used:* Siglent SDS804X HD Oscilloscope* Siglent SDG1032X HD GeneratorSettings:* PRP1 zeroed out on Oscilloscope with 0V input* 0.1 Hz square wave* 100mV peak to peak* 0V offsetPass criteria:Measured 100mV peak to peak on the oscilloscope on CH1 and CH3\Two measurements are 5% within each other## 5) Cancellation range +24V and -24VVerifies the +/-24V Cancellation range of the PRP1\!(5.png)\Equipment used:* Siglent SDS804X HD Oscilloscope* Rigol DP832 Power supplySettings:* PRP1 zeroed-out after each change of the voltage on power supply* Set up 5V, 12V, 24V with 0.1A current limit on power supply* Flip BNC to banana adapter and repeat measurementPass criteria:PRP1 can be adjusted to less than 100mV measured on the oscilloscopeOutput current of the power supply is less than 1mA## 6) 500mV dynamic rangeVerifies the active signal range of the PRP1\!(246.png)\Equipment used:* Siglent SDS804X HD Oscilloscope* Siglent SDG1032X HD GeneratorSettings:* PRP1 zeroed out on Oscilloscope with 0V input* 0.1 Hz square wave* 500mV peak to peak* 0V offsetPass criteria:Measured 500mV peak to peak on the oscilloscope## 7) DC input 50KOhmVerifies the 50KOhm input impedance in DC conditions of the PRP1\!(7.png)\Equipment used:* Siglent SDS804X HD Oscilloscope* HP 34401A multimeterSettings:* PRP1 zeroed out on Oscilloscope with 0V input* resistance measurement auto rangePass criteria:50Kohm +/- 2% measured on DMM## 8)a VNA bandwidth 10MHz-3 GHzVerifies the minimum 2 GHz bandwidth of the PRP1\!(8a910.png)\Equipment used:* LiteVNA* Rigol DP832 Power supply* MegiQ VNA calibration kit* LiteVNA SS405 Coax cablesSettings:* 10 MHz to 3 GHz sweepPass criteria: 1dB maximum deviation between minimum and maximum of S12 up to 2 GHz\Nominal gain is -2dB +/- 1dB\Note: 1.3:1 is 0.77 or -2dB## 8)b VNA bandwidth 400MHz-3 GHz 2nd setupVerifies the minimum 2 GHz bandwidth of the PRP1 with a more accurate VNA\!(8b.png)\Note: Minimum frequency setting of the VNA is 400 MHz\Equipment used:* MegiQ VNA-0440e* Rigol DP832 Power supply* MegiQ VNA calibration kit* LiteVNA SS405 Coax cablesSettings:* 400 MHz to 3 GHz sweep* S11,S12 measuredPass criteria: 1dB maximum deviation between minimum and maximum of S12 up to 2 GHz\Nominal gain is -2dB +/- 1dB## 9) S parameters!(8a910.png)\Equipment used:* LiteVNA* Rigol DP832 Power supply* MegiQ VNA calibration kit* LiteVNA SS405 Coax cablesSettings:* 10 MHz to 3 GHz sweepPass criteria: NoneS parameters provided for reference## 10) 50 Ohm loading at high freqency, VSWR!(8a910.png)\Equipment used:* MegiQ VNA-0440e* Rigol DP832 Power supply* MegiQ VNA calibration kit* LiteVNA SS405 Coax cablesPass criteria: VSWR < 1.5 up to 2 GHz\This is equivalent to Return loss < -13dB\Or capacitive loading of ~ 0.5pF## 11) Noise measurement 1GHz BW 8 bit scopeVerifies the high freqency noise content of the PRP1\!(31112.png)\2 GHz scope should be used for ideal conditions, but I don't have access to one\Equipment used:* Keysight MSOX 3104T Oscilloscope* Keithley 2221A Power supplySettings:* PRP1 zeroed-out* PRP1 powered by lab linear power supply* PRP1 input shorted by SMA shoring plug or 50Ohm load* 2 mV/div on CH1 and CH3* 1 ms/div time scale* 50 Ohm input on scopePass criteria:TBD## 12) Power consumption!(31112.png)\Equipment used:* Siglent SDS804X HD Oscilloscope* Rigol DP832 Power supplySettings:* 5V, 0.1A* PRP1 zeroed-outPass criteria:Power consumption less than 20mAManaged to write frequency wrong 3 different ways.

author: tszaboo
author_rank: Super Contributor
timestamp: September 24, 2024, 11:03:20 am
content: https://github.com/tszaboo/PRP1I've placed the following on Github:User manualDesign verification test resultsDesign verification updated guideImportant change that I increased the specification for the noise. I originally measured the noise with 1:1 setting and that's technically not correct, since it's a 1.3:1 probe, therefore the new specification is 65uV 20MHz.For me, this concludes the design verification phase.I'll continue to assemble the PRP1s, test them, and to order the accessory cables. One cable I also need to make myself.Please see below an extra oscilloscope shot I made during the verification. It's noise coming from an USB power supply CH1 measuring it with regular oscilloscope probe, CH3 with the PRP1 with the 2.54mm to SMA cable. We can see how significantly less noisy the PRP1 is compared to a standard probe.

author: 2N3055
author_rank: Super Contributor
timestamp: September 24, 2024, 11:47:05 am
content: Quote from: tszaboo on September 24, 2024, 11:03:20 amJust wanted to say, nice work !!Results look quite good.

author: tszaboo
author_rank: Super Contributor
timestamp: September 30, 2024, 08:38:09 am
content: I had some time this weekend to test and put together the first batch.I'm still waiting for the cables and a sample of the shipping box.I expect I can call these ready in about 3 weeks time.

author: Martin72
author_rank: Super Contributor
timestamp: September 30, 2024, 09:28:39 pm
content: What would it cost?Since reading this article, I have become very interested in it:https://www.siglenteu.com/power-integrity-measurement-solution/

author: tszaboo
author_rank: Super Contributor
timestamp: October 01, 2024, 10:25:39 am
content: Quote from: Martin72 on September 30, 2024, 09:28:39 pm250 EUR + Paypal and shipping fees.Siglent is very right about those measurements. Switching noise can and will couple into passive probes. You are trying to measure ripple on a power supply rail, but those spikes make it impossible, since they superimpose and make a few millivolt ripple into hundreds of millivolts of noise spikes. Often times it's so short and it lines up with your trigger, you don't even see it on the scope screen. Plus, thats not what's on your board, it's something that couples into your 1MOhm/10MOhm passive probe as EMI.Now, power rail probes that are made for your scope are great, and if you (your company) can afford one, buy that. It shows the DC component, tells you if the probe is in overload. Much better for reporting and design verification. And they have cable compensation, or DC calibration. But they are very expensive. The PRP1 won't show you the DC offset on the screen, or tell you if it's in overload. So you have to be aware of the limitations. On the other hand, you can see from the scope screengrabs that I posted, it's less noisy than a x10 probe, and doesn't show the EMI switching noise.

author: tszaboo
author_rank: Super Contributor
timestamp: October 01, 2024, 02:56:07 pm
content: I've finally had time to finish the remaining test, the second VNA measurements with a higher quality VNA (Megiq). I could do a sweep between 400MHz and 4GHz on 3600 points, so every MHz.S11, SWR and others are just informative, this is not a pure 50 Ohm system since the source impedance is 0 Ohm and the load is 50 Ohm, and I have parts in series. But it's still tells a bit about the system performance, so I included it.More important is the gain VS frequency. Nominal gain is 1.3:1 or -2dB. Normally scope manufacturers define the bandwidth of a probe or a scope at the -3dB point compared to the nominal gain. The -1 dB point is 2.7GHz for this probe, and the -3dB is over 4GHz, meaning that the probe fulfills the 2GHz design requirement. I doubt that there are many people with 2GHz+scopes that would be interested in buying this.The choice of cabling and the scope's internal 50 Ohm (or external 50 Ohm) will be the limiting factor in all cases.

author: tszaboo
author_rank: Super Contributor
timestamp: October 04, 2024, 04:22:44 pm
content: Cables arrived, packaging sample arrived, and it's a nice one.I only have to order a bit more from the packaging and I'll be ready to ship out the first batch.

author: Martin72
author_rank: Super Contributor
timestamp: October 04, 2024, 05:01:38 pm
content: Looks really good

author: tszaboo
author_rank: Super Contributor
timestamp: October 21, 2024, 07:10:32 pm
content: So after some family stuff and then some sickness, I'm ready to continue.First batch is almost ready. I can send them out this weekend maybe early next week.I'm accepting orders for the first batch now. PM me.Price is 250 EUR + payment and shipping fee. Shipping is calculated as DHL smallest package from Netherlands.

author: Kean
author_rank: Unknown
timestamp: November 04, 2024, 12:45:19 pm
content: I received my PRP1 today. It will be a few days at least before I can spend time with it, but it looks great.A few pics are attached in case anyone is curious, but I have not taken it apart... yet...

author: tszaboo
author_rank: Super Contributor
timestamp: November 11, 2024, 08:11:59 pm
content: Hi, some update. I've sent the first few PRP1s to people who ordered it. I have just 3 of the batch left.If I decide to do another batch that's likely to only happen in 2025, and probably going to be a group buy, so it could be a while.

author: scottapotamas
author_rank: Regular Contributor
timestamp: December 04, 2024, 12:07:20 pm
content: Mine arrived the other day and I had a quick moment to get familiar with it today by doing somequickmeasurements.In short, does what I expected so far and matches the described specifications well enough. I'm looking forward to using it seriously, and happy to add it to the toolbox.Overall a solid first-batch of a hobby(?) project. Throughout the process (questions prior to purchase, ordering/shipping) tszaboo was helpful and responsive!I'll come back after I've used it enough with real projects to actually provide valid feedback.Tried to match test setup against tszaboo'spublished setups as per GitHub docScreenshots attached are named accordingly.DC Resistance - 49.9829 kΩ when zeroed, 4-wire measurement on 2701.Power consumption - 5.004 V from DP832. 13.201116 mA measured with 2701 (filtered, 5 PLC)All tests were done with a lab PSU providing 5V rather than scope USB.My scope doesn't support 1.2 input attenuation. Both channels are left at 1x, 50 Ω internal, no BW limit unless mentioned.The PRP1 is always on CH1.Used my own BNC and SMA cables, adapters etc. All first owner+name RF brands etc, all overkill for >6 GHz work.I noticed during the gain test that my sig-gen (DG1022) wasn't too great at hitting the Vpp setpoints. The output BNC was into a tee then connected to the PRP1 and CH2 as reference. I'd expect relative comparisons to be OK.I'll try to setup the RSA to look at spectral performance and attemptcrudereplications of the VNA measurementsThere are some screenshots of a quick real-world setup looking at the output of a 12 V buck-boost reg built on the TI TPS552892.It's running in step-down PWM mode with a 2 A load, and I've intentionally removed the snubbers on the switching nodes.The SMA pigtail included with the PRP1 kit is connected (poorly) to PTH testpoints on the output.A 10 MΩ passive probe (CH2) using the default ground antenna/clip is poking at the same output test-point.Because the rail is around 12 VDC, CH2 hits the 10 V vertical offset limit and can't be used with DC coupling and a sensitive scale at the same time.The coarse+fine offset of the PRP1 handles this as expected, while showing a better representation of the signal.The screenshot can't show it, but the blue CH2 trace can be influenced by handling the probe cable. Becoming a human radiator/capacitor by holding a finger to some parts of the board picks up a lot of unwanted noise. The PRP1 waveform is unchanged and robust.

author: tszaboo
author_rank: Super Contributor
timestamp: December 04, 2024, 12:48:33 pm
content: Quote from: scottapotamas on December 04, 2024, 12:07:20 pmMany thanks for the detailed write up, I'm glad you find it useful.I use "Custom" attenuation on the oscilloscopes that I tested the unit on. If that's not supported, than a Math channel could be used for the probe attenuation. I think on some scopes you might even add the DC offset in with the Ax+B computation, and get the correct values on the screen.Quote from: scottapotamas on December 04, 2024, 12:07:20 pmSignal generators expect 50 Ohm load on their output. The PRP1 load is never really 50 Ohm, it's somewhere between 60-50KOhm depending on the frequency, by design (that's the whole point of it). I had a bit of trouble making the test setup first, until I realized I would need a source with 0 Ohm output, or do a relative measurement.

author: scottapotamas
author_rank: Regular Contributor
timestamp: December 04, 2024, 01:38:26 pm
content: Quote from: tszaboo on December 04, 2024, 12:48:33 pmI don't believe I have a custom attenuation setting unfortunately, though I should try abusing probe compensation settings.Ax+B isn't a great on this scope and most of my troubleshooting or tuning can tolerate relative measurements most of the time.Quote from: tszaboo on December 04, 2024, 12:48:33 pmYeah. I had the sig-gen set to 50R output to drive the scope's 50R, and basically just let the PRP1 hang off the tee. It should only be a few milliohms off so I didn't expect >5% error on the scope Vpp.Saying that, 8-bit scopes aren't great tools for precision voltage measurements and the arb probably needs a closer look because it's spent a few years acting as a glorified TTL/LVCMOS pulse generator.: Just checked the DG1022Z's 50R output spec and it's±(1% of the setting value + 5mV + 0.5% of the amplitude)which explains it. Sorry for the off-topic clutter.

author: scottapotamas
author_rank: Regular Contributor
timestamp: July 03, 2025, 02:26:00 am
content: Hasn't been much discussion here, but will add some thoughts now I've gone through a few different designs with the PRP1. I'm very happy with it overall.I've used it to look at input/output noise on a high-power buck-boost reg, validate the spread-spectrum behaviour of a regulator, several buck-LDO rails, before/after ferrites on a dual-loop PLL IC's power rails, checking for supply transients from high-speed digital blocks, etc. A few examples setups are attached.Using the PRP1, I was able to find/document/resolve one of my PLL clocks bleeding (~1.9Ghz and -75dBm) into a supply rail. This is not something my passive scope probes can do, it's rather difficult to see with near-field probes, and it's not going off-board so a RF current probe isn't practical (mine are too slow anyway).I didn't expect to find it as useful for quick documentation with the spectrum analyser though (after zero-ing with the scope, DC-block inline), there's nearly no setup variation and far less time-consuming compared to setting up the LISN or TEM cell. Great for something non-critical or when tuning configuration passives etc.I've have some minor workflow edges with the PRP1, which is more a reflection on my use-case than the probe design itself.Often ended up with one of the offset knobs needing to be setjuston it's detent position, where the knob wants to shift slightly after release in those ranges.I use SCPI scripts to automate most of my measurements for documentation. For the output ripple analysis of a regulator this isn't an issue because it's stable enough across the sweep parameters, but in a test where the input voltage is swept I had to make a variant script that waits for me to manually zero out the PRP1 between each runMy scope doesn't support arbitrary attenuations, but I just handle this on in my custom plotting workflow instead. The SA supports 3-sf 'external gain' settings so that one's easy at least.I've used a far more expensive probe at a previous workplace which handled offset voltage configuration on the scope, which might be why this is what I'm noticing the most. If a 'digital version' was available in roughly the same magnitude of price but with a 'zero button' and/or software controllable offset voltage instead of the knobs I'd jump on it pretty fast.

author: tszaboo
author_rank: Super Contributor
timestamp: July 07, 2025, 02:12:52 pm
content: Quote from: scottapotamas on July 03, 2025, 02:26:00 amThanks for the feedback. I've decided to work on the current version and make this available for more people. It's not economic for me to handle the assembly myself, so I will outsource it. And in the meantime focus on improving it. Making it digital would be a good improvement, I've already looked into it a few months ago and have some simulations and schematic on how to do it. The potentiometers would be replaced with a single pushable rotary encoder, and some USB communication would be a plus.