Picotest Injector Teardowns - Page 1
Forum section: electronics / testgear

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: April 10, 2020, 12:05:00 am
content: Hello All,I am not sure if this is the best place to start a discussion about PicoTest Line Injectors. They are useful tools, but tend to be on the expensive side. I wanted to upload what I have to be archived, and for those who wish to design their own or at least are interested in such topics. I hope this helps someone, somewhere.Picotest J2120A Line InjectorPrice: $525BOM:(4) CapacitorsC1||C2 = 35.7uFC3||C4 = 1.98uF(1) Resistor10k(1) nMOSAOT2618 from Alpha and Omega Semiconductor,http://www.aosmd.com/res/data_sheets/AOT2618L.pdfJ2120A front and rear pics attached.Picotest J2130A DC Bias InjectorPrice: $525BOM:(24) CapacitorsParallel, Series network = 27uF(1) Resistor10kI do believe the equivalent network of the 24 caps is 27uF, I may wish to double check when I get a chance.J2130A front and rear pics attached.Ridley Injector Isolator TransformerNo specifications really. The manufacturer looks to be Avel Lingberg.Model CA8518.I hope this comes out clean, first time poster. Hell of a time with the pics.*EDIT*Added front picture of the J2120A.

author: Sighound36
author_rank: Frequent Contributor
timestamp: April 10, 2020, 12:44:44 pm
content: Hello 16BitanalogueThis was going to be a couple of my next purchases much appreciated.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 10, 2020, 12:55:42 pm
content: 16bitanalogue,Thank you for the teardown pictures and welcome to the group.Quote from: 16bitanalogue on April 10, 2020, 12:05:00 amYou seem to be missing the J2120A front picture, showing the AOT2618 MOSFET.Do you have the J2111A Current Injector in your collection? I would like to see teardown pictures.Thanks!!Regards,Jay_Diddy_B

author: fcb
author_rank: Super Contributor
timestamp: April 10, 2020, 03:08:34 pm
content: Great first post.The Ridley Injector unit (in blue) is still PatPending (and has been since at least 2010 - no sign of an actual granted patent), looks like it might have a second transformer (3E27 - which is MnZn core material) to handle the HF.Whilst none of these boxes look like good-value, the BOM cost on the Ridley Injector ($600) unit is much higher than the Picotest ($525+) units.Ridley videos on YT are pretty interesting.

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: April 10, 2020, 07:46:54 pm
content: Quote from: Jay_Diddy_B on April 10, 2020, 12:55:42 pmI added the front picture of the J2120A to my first post.I did manage to capture tear down information for the J2112A High Current Injector which is the big brother of the J2111A. I stashed the penciled schematic, BOM, and pictures somewhere. I will have to see where I squirreled them away, but if not I will have to capture them again.I realize that most of these have a hell of a markup (engineering effort, mechanical design of the box, etc.), but it is certainly worth a DIY solution.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 10, 2020, 08:03:46 pm
content: Hi group,Here is the J2120A schematic:Regards,Jay_Diddy_B

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: April 10, 2020, 08:10:18 pm
content: Picotest J2112A High Current InjectorPrice: $1,995BOM:I will need to go back and measure the components. I lost that information. It is also difficult to see the part number on the SOIC8 - I want to recall it was an op-amp of some kind.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 10, 2020, 08:27:04 pm
content: Hi group,For the J2130A the insertion loss is given as:Working backwards from this the capacitance is 28.2uF with zero bias.so 12x 4.7uF in parallel, 2 sets in series.So we have:Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 10, 2020, 08:59:36 pm
content: Quote from: 16bitanalogue on April 10, 2020, 08:10:18 pmThis looks like this:This is basically a current sink that can work with either positive or negative inputs:Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 11, 2020, 01:00:39 am
content: Hi group,**** Error - See this Message ****https://www.eevblog.com/forum/testgear/picotest-injector-teardowns/msg3011600/#msg3011600*****************************Here is a working model that comes close to matching the specification that are published by PicoTest.https://www.picotest.com/images/download/j2112a-spec-sheet-final-hires.pdfLTspice ModelThis is using one of the op-amps available in LTspice.Simulation ResultsI have attached the LTspice model.Regards,Jay_Diddy_B

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: April 11, 2020, 04:41:40 pm
content: I believe I can get a hold of a few more Picotest injectors.I am hoping there is a J2110A floating around and the common mode transformer J2102B.I'll try to keep this updated as they come.

author: Sighound36
author_rank: Frequent Contributor
timestamp: April 11, 2020, 04:50:03 pm
content: Thanks for all your efforts chaps first class.Howabout a group design and build?

author: 2N3055
author_rank: Super Contributor
timestamp: April 11, 2020, 05:55:58 pm
content: Fantastic topic!! Great work here!!

author: Ribster
author_rank: Frequent Contributor
timestamp: April 11, 2020, 07:27:58 pm
content: I can design and assemble some boards if you guys are interested..

author: Sighound36
author_rank: Frequent Contributor
timestamp: April 11, 2020, 10:37:23 pm
content: More than happy with that thank you

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 11, 2020, 11:13:02 pm
content: Hi group,Just playing around in KiCAD:This software is new to me. I normally use something else.100mm x 100mm board, no case.Which injectors are the most useful?Regards,Jay_Diddy_B

author: Sighound36
author_rank: Frequent Contributor
timestamp: April 12, 2020, 05:22:15 am
content: Hi Jay_Diddy_BThank you for your efforts personally I would interested in all of them however the Picotest J2120A Line Injector would be a great place to start

author: _Wim_
author_rank: Super Contributor
timestamp: April 12, 2020, 05:47:55 am
content: Quote from: Ribster on April 11, 2020, 07:27:58 pmI am also interested in these!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 12, 2020, 10:58:48 am
content: Quote from: 16bitanalogue on April 10, 2020, 08:10:18 pmThe pictures that were included are actually the J2111AI was having difficulty getting the component values, that I can read in the photograph, in the model agree with the datasheet performance.This are the specifications:LTspice model J2111AAnd the modelling results:I have attached the LTspice model.Regards,Jay_Diddy_BJ2111A concept model.asc(5.46 kB - downloaded 167 times.)

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 12, 2020, 04:30:16 pm
content: Quote from: Sighound36 on April 12, 2020, 05:22:15 amHi,I am a few hours into using KiCAD. This what I have come up with for the 2120A:I am showing the IRF540, but the plan is to use the AOT2618.The artwork is single-sided:The board is 100mm x 100mmThe plan is to use Keystone 575-4 for the connections.Comments?Jay_Diddy_B

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: April 12, 2020, 10:14:17 pm
content: Quote from: Jay_Diddy_B on April 12, 2020, 10:58:48 amOops! I couldn't remember which version since it has been several months. The performance is really close to the datasheet, so I would move forward with what you have. In the future, I can update with actual measured values and track down the op-amp that is being used. It may be moot, but I'll be happy to do it.According to the User's Manual for the Signal Injectors, the J2111A is bi-directional; i.e., it can only SINK current up to 100mA with positive and negative voltages. Where as the J2112A can SINK up to 1A with positive voltages only.

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: April 12, 2020, 10:36:54 pm
content: Quote from: Jay_Diddy_B on April 12, 2020, 04:30:16 pmI am personally partial to Keystone 7006 and 7007, but for low cost purposes the 575-4 are good.2-layer, FR4, 1oz copper top pour.

author: Wolfgang
author_rank: Super Contributor
timestamp: April 13, 2020, 12:13:11 am
content: Quote from: 16bitanalogue on April 12, 2020, 10:14:17 pmWhen trying to build your own, watch for two pitfalls:- The part has a dead zone at small voltages where the current drawn is completely incorrrect, even if the sense resistor says its OK.- Have a look at the transistor datasheets. They will die if you draw max. current (dynamic plus offset) at 40V. If you want to keepthis spec, you need better transistors and better cooling.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 13, 2020, 03:03:06 am
content: Quote from: Wolfgang on April 13, 2020, 12:13:11 amWolfgang,Thank you for the guidance. The cooling for the transistors is certainly inadequate for 3W of dissipation.And yes there is a dead band where the devices doesn't work properly.My interest in building these is to find out what they can do.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 13, 2020, 03:32:51 am
content: Hi,Further to my last reply, the manual that can be found here:https://www.picotest.com/support.htmlOn page 44 it says the maximum input voltage is DC + AC is 5V5V x 74mA = 375mWThis is consistent with the transistor selection and mounting method.Regards,Jay_Diddy_B

author: Sighound36
author_rank: Frequent Contributor
timestamp: April 13, 2020, 10:44:40 am
content: Some good investigational work there chaps.Personally if going to this detail I would rather over engineer the the whole thing using much better specifications on not just the parts but the board and box. My personal thoughts

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 13, 2020, 11:25:44 am
content: Hi,Quote from: Sighound36 on April 13, 2020, 10:44:40 amI would be interested to know fromusersof the PicoTest injectors which ones arereallyuseful and what improvements are desirable.I have built and used:1) Injection transformer for loop measurements - many times2) PSRR measurement device - Occasionally only with high performance LDOs3) High Frequency Injector (AC coupled) for looking at capacitor impedance and PDN. (Very Occasionally)I have never looked at power supply stability by looking at output impedance in the frequency domain. I have done many measurements with a stepped load current. This is really the same thing in the time domain.Any users out there?Regards,Jay_Diddy_B

author: Sighound36
author_rank: Frequent Contributor
timestamp: April 13, 2020, 12:46:30 pm
content: I can see 1 and 2 being very useful for a lot of folks here.So the J2120A and the J2130A would be my first suggestions

author: Wolfgang
author_rank: Super Contributor
timestamp: April 13, 2020, 03:35:54 pm
content: Quote from: Jay_Diddy_B on April 13, 2020, 03:32:51 amIn my J2111A manual the *output* voltage (and its not the input voltage that counts here) is 40V. So the power is way too much.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 13, 2020, 04:54:46 pm
content: Quote from: Wolfgang on April 13, 2020, 03:35:54 pmWolfgang,You are right.It is not all that clear in the manual and the datasheet which limits apply to which connector.By "input" they seem to be referring to the modulation input.By "output" they are referring to the part that connects to the device under test.From the teardown photographs of the J2111A 40V transistors are used CZT3904 and CZT3906.If you apply 40V output and turn on the bias, there will be nearly 1W dissipated in the transistor. If you apply a signal to the modulation input then it increases.There is no mention of power limit at all.I am not recommending this architecture, I am exploring its performance and limitations.Regards,Jay_Diddy_B

author: Wolfgang
author_rank: Super Contributor
timestamp: April 13, 2020, 06:09:38 pm
content: Quote from: Jay_Diddy_B on April 13, 2020, 04:54:46 pmHi,they idea to use a fast op-amp and a medium speed transistoris fine and has been discussed in many textbooks.The technique to serve both polarities (with a dead zone) is something I almost never need (positive would suffice).This would save you a diode drop in compliance. Speed is fine, but it is only realistic if you have absolutely *no* wiringbetween DUT and injector (I used plug shorts). Otherwiese the 40MHz are not reacheable.https://electronicprojectsforfun.wordpress.com/measuring-a-picotest-j2111a-current-injector/I mostly work with linear, low noise PSUs so I dont need 40MHz BW. What I would need is a higher voltage/current rating.I tried D44H11, which is OK up to a few MHz, 60V/120mA, and that worked OK.RegardsWolfgang DL1DWG

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: April 13, 2020, 06:20:31 pm
content: Quote from: Jay_Diddy_B on April 13, 2020, 11:25:44 amEven though I have access to the injectors, I have not used them myself. I honestly do not need them for the devices I design and support. I have used the Ridley Injection Transformer with the Bode-100 for stability analysis extensively. To help correlate in the time domain, I use a power FET and a AWG to smack the output with a transient load, but it is an open loop design and is very manual to set up.My colleagues may have their own nitpicks, but two things come to mind:1. J2120A - by its very nature is passive and was intentional (side conversation with Mr. Sandler). In other words, one would need to use FORCE/SENSE to compensate for any drops over load current. Pictotest also has an application note as well that explains this. I am not sure we can do anything better and maintaining the passive nature of the design.2. IMO, this exercise is one of cost reduction plus the fun benefit of revealing the circuit and knowing how it works.3. I also agree with SigHound, let's improve where we can and it looks like the current injectors could benefit from increased power dissipation. I suspect the J2112A is of similar design, just capable of increased power dissipation since it can sink 1A.I would like to get a hold of their FETSlammer which I suspect is a closed loop design (HS op-amp and a power FET) where the edge rate and V/A is proportional to the fungen output.

author: Sighound36
author_rank: Frequent Contributor
timestamp: April 13, 2020, 06:24:34 pm
content: You could try a BDX33C and use a heat-sink that handles up to 5amps no problem BW is sufficient to.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 21, 2020, 11:31:20 pm
content: Hi group,been busy with KiCAD and Fusion 360.Any interest in this project:This is a blocking capacitor and bias injector.Regards,Jay_Diddy_B

author: Wolfgang
author_rank: Super Contributor
timestamp: May 22, 2020, 12:17:45 am
content: Is this a bias Tee ? Where is the decoupling inductor ?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 22, 2020, 12:34:23 am
content: Hi,Just a resistor 10k, R1 similar to commercial products.I could add pads for an inductor to make it more versatile.Jay_Diddy_B

author: Sighound36
author_rank: Frequent Contributor
timestamp: May 22, 2020, 06:47:05 am
content: Yes I am interested Jay thank you

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 22, 2020, 12:16:27 pm
content: Hi,an inductor has been added in parallel with the resistor.The pads have been sized so that a 6mm, 7mm or 10mm inductor will fit.I have also added four 3.5mm diameter mounting holes.Any other ideas?Jay_Diddy_B

author: Wolfgang
author_rank: Super Contributor
timestamp: May 22, 2020, 01:37:03 pm
content: ... what does your VNA say to this one ?... how much current does the inductor tolerate before saturating ?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 22, 2020, 03:16:48 pm
content: Hi Wolfgang,I didn't pick an Inductor I just left space for one.I think the BNC or SMA connections limit the current.Do you have any inductors you like for this?Jay_Diddy_B

author: Wolfgang
author_rank: Super Contributor
timestamp: May 22, 2020, 03:43:03 pm
content: Hi Jay,in fact I made some bias tees for the very low end (10kHz - 200MHz).The purpose was to support a transistor device parameter extraction with a VNA, and the bias tees were used toset the operating point. These bias tees are tricky because of the very broad range.If you want I send you a schematics.Higher frequency stuff is easy. Mini-Circuits has parts going up to many GHz.regardsWolfgang

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 22, 2020, 04:00:54 pm
content: Wolfgang,I don't think that this is a well designed bias tee for high frequencies.There will be a 'bump' where are all the capacitors are connected in parallel.I would do a different design with Coplanar Waveguide for high frequencies.Please share your schematic (you can PM me if you like).Jay_Diddy_B

author: Sighound36
author_rank: Frequent Contributor
timestamp: May 22, 2020, 05:05:34 pm
content: Hindsight being a great thing!Realistically Wolfgang what do you feel is a lower limited that would be useful in with this particularly application?Or would designing a seperate bias tee as an add on would be more beneifcal?ThanksSighound

author: free_electron
author_rank: Super Contributor
timestamp: May 22, 2020, 05:33:38 pm
content: why dont you combine several of these into 1 unit ? or make a 'breakable' circuit board.

author: Wolfgang
author_rank: Super Contributor
timestamp: May 22, 2020, 06:10:48 pm
content: @ to allThe art of bias tees is complex because all elements (series Cs, Ls, ...) have parasiticsand what you dont want is a high-Q resonance *anywhere* in your passband.So the trick is to start with the high frequency end, accept some losses to keep resonances low,and add section per section with larger Ls and Cs until your low frequency corner is acceptable.The more sections, the lower the frequency, the larger the inductors get and this increases DCresistance, something you also dont like.If the lower limit is in the 100s of Hz, you would combine passive LCRs with active bias Tees (Op amp voltageregulators where the regulator has a cutoff where you need it.I will put some info on my website the next few days (schematics, photos, VNA measurements, ...).regardsWolfgang

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: May 22, 2020, 07:33:40 pm
content: Quote from: Jay_Diddy_B on May 21, 2020, 11:31:20 pmYes, very interesting indeed! Just found this thread. Great work! I made my own PSSR tester since the picotest unit was far to expensive for me. Ended up doing pretty much what Ti suggested:http://www.ti.com/lit/an/slaa414a/slaa414a.pdf?ts=1590175942099

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 23, 2020, 02:20:39 am
content: Hi,Let me share a few measurements made on the prototype:This is a picture of the prototype. It was milled on double sided FR4 PCB. The board is 100mm x 100mm0 - 200MHzA DSA815-TG was used for the measurement. The setup was normalized with a BNC barrel connector.The Bias tee is almost perfectly flat in the frequency range 0 - 200MHz.This was confirmed using an HP3577A VNA0 - 1.5GHzThe frequency range was widened to 1.5 GHzThere is a notch at 922MHzAfter a little while I realized what was causing this.I tested a BNC tee piece with an 8cm length of RG316 coax on one limb.This is the result:A notch at 625MHzThis notch is when the open length of the line is 1/4 of wavelength.3 x 10E8 /625 x 10E6 = 48cm1/4 wavelength = 12cmvelocity factor = 0.66It kind of works out.At 922MHzwavelength = 3 x 10E8 / 922 x10E6 = 32cmquarter wavelength = 8cmOpen circuit transmission lineThe resistor needs to be moved closer to the capacitors.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 23, 2020, 02:40:23 am
content: Hi,The bias line was cut in this location:And the measurement repeated:Same vertical scale 5dB/divConsiderable improvement.Some of the other 'wiggles' will go away if I have more vias between the top and bottom planes.Regards,Jay_Diddy_B

author: Sighound36
author_rank: Frequent Contributor
timestamp: May 23, 2020, 09:08:30 am
content: Hi JayAs with all things RF, some of the smallest movements generator some of the most obvious gains.Great work

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 27, 2020, 03:42:02 pm
content: Hi,I have continued to look at this.I have been thinking about the best way to connect the large number of capacitor in series / parallel and maintain a controlled impedance.PCB DesignPrototype boardThe board was made from 0.062 FR4 on my LPKF Protomat c60.Board AssemblyI inserted some of the 'via wires'MeasurementI used an HP 8714 for the measurement:This is 3mHz to 3GHz 2dB/div.looking good!!Jay_Diddy_B

author: Sighound36
author_rank: Frequent Contributor
timestamp: May 27, 2020, 03:47:17 pm
content: Pretty respectable trace there for a 3Ghz bandwidthOk not being an RF guy, so shoot me, would it not be better to have less capacitors with a larger value? Or is this a fundamental issue with this portion of the design?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 27, 2020, 06:11:30 pm
content: Quote from: Sighound36 on May 27, 2020, 03:47:17 pmThe capacitors I used are each 10uF 50V X5R 1210. The idea of such a high value is to get a low frequency -3dB point.12 x 10uF / 2 = 60uFR= 25F = 1/(2 x Pi x R x C) = 26.5 HzRegards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 27, 2020, 06:17:21 pm
content: Hi,Here are some TDR measurements made with a Tektronix 11801 and SD24 sampling head.The Bias injector was place between two lengths of semi-rigid 50cables:From left to rightThe 50 Ohm cablethe first 'wiggle' is the transition from the cable to the board, the SMA edge launch.Then a short piece of 50 Ohm track.two sections of 45 Ohms, about 25mm long, where the capacitors are50 Ohm trackSMA connector50 Ohm cableI have marked the measured impedances on this drawing of the board assembly:to raise the impedance where the capacitor are, I need to widen the gap between the traces and the ground plane.Regards,Jay_Diddy_B

author: Sighound36
author_rank: Frequent Contributor
timestamp: May 27, 2020, 06:44:15 pm
content: In a very crude way that is the situation I was attempting to elude toGreat stuff Jay, really do not know where you find the time but top man

author: 2N3055
author_rank: Super Contributor
timestamp: May 27, 2020, 10:06:06 pm
content: Nice demonstration of usefulness of TDR..Great work (as always!!) Jay..Regards,Sinisa

author: tv84
author_rank: Super Contributor
timestamp: May 27, 2020, 10:14:41 pm
content: Quote from: Jay_Diddy_B on May 27, 2020, 06:17:21 pmDamn! This is an optimization of my suggested change!!!Respect!(I had removed it because, afterwards, I thought it was something irrelevant... )

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: June 02, 2020, 04:08:22 pm
content: Quote from: 16bitanalogue on April 10, 2020, 12:05:00 amAnother nice one would be the "2180A" preamplifier to up the sensitivity of 8bit scopes. I wonder how they have done it in such a small package.

author: corecode
author_rank: Newbie
timestamp: October 13, 2020, 10:02:14 am
content: Could somebody explain what R1, R2, and C1 are being used for? R2/C1 look like some sort of high frequency roll-off, but at a surprisingly high frequency.Thanks!Quote from: Jay_Diddy_B on April 12, 2020, 10:58:48 am

author: Wolfgang
author_rank: Super Contributor
timestamp: October 13, 2020, 01:01:30 pm
content: Quote from: corecode on October 13, 2020, 10:02:14 amR1, R2 and C1 are needed to prevent HF oscillations. Its more or less an output damper.Whats also interesting is that the circuit has a dead zone around 0V. Even if the current monitor output will be OK,the sunk current is not. The manual did not show this until a few months ago.https://electronicprojectsforfun.wordpress.com/measuring-a-picotest-j2111a-current-injector/

author: corecode
author_rank: Newbie
timestamp: October 13, 2020, 01:11:41 pm
content: Thanks for the quick answer.I'm simulating a simplified circuit (no diodes, just sink from positive rail, different op amp (OPA358)) to understand the circuit and trade-offs. However, I get peaking without C2, and with C2 I get a roll-off starting around 1MHz. I guess I need to pick a different op amp?

author: Wolfgang
author_rank: Super Contributor
timestamp: October 13, 2020, 03:25:09 pm
content: Yeah, the output network is a compromise between 3dB frequency and stability. It needs to be matched to the OpAmp, thats correct.And dont forget to simulate with all kinds of DUT PSU output impedances !

author: corecode
author_rank: Newbie
timestamp: October 14, 2020, 08:39:40 am
content: This is what I have come up with so far; crossed out components are not part of the simulation.Looks like R13/C1 is to compensate possible L1 wiring inductance going to the DUT.I will simulate various DUT impedance configurations next.I wonder whether I should add an additional op amp to optionally boost the Pr1 output gain. In general, I'm surprised by the signal level choices of the original design.

author: corecode
author_rank: Newbie
timestamp: October 14, 2020, 01:08:04 pm
content: Quote from: corecode on October 14, 2020, 08:39:40 amDoesn't look too bad - of course the wiring to the DUT has a huge impact at the high frequencies.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 14, 2020, 01:40:02 pm
content: When you look at my webpage about it you see that the PicoTest risetime claims are only realistic if there is less than 2-3cm of wire length between output and DUT. This will not be possible in a lot of cases. IMHO, it is smarter to live with reasonable bandwidths (0-5MHz) and better stability. Most injectors are used to determine the response of switching regulators. Their regulator loop bandwidth (not the switching frequency) is normally far below 100kHz, so a few MHz of injector bandwidth is good enough.

author: corecode
author_rank: Newbie
timestamp: October 14, 2020, 02:08:23 pm
content: I agree. This was mostly an exercise to understand the limits of this approach. It would be nice to observe most of the PDN performance at the supply vias of a chip. I don't have a good FRA/VNA anyways, so this probably will be good enough to be used with my RTB2004's K36 option.Latest design attached (qucs-s). Maybe I'll get around to building it.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 14, 2020, 04:41:53 pm
content: Testing PDNs is a tough test because of extremely low impedances here. Tests leads from your injector to the board are simply a no-no. Another challenge is that modern FPGAs draw 10s of amps at *very* low voltages. To make this move, you need to inject several Amps right at the DUT, asking for a very compact, solder-in solution for the injector and the same for the probe. This smells like copper-base PCBs, very modern switching MOSFETs in small cases, super-compact, all SMD designs, and so on. A funny challenge, but certainly not easy. An alternative for directly soldering the injector and the probes into the circuit is ultra-low inductance coax.

author: Peter_Clements
author_rank: Newbie
timestamp: September 15, 2021, 02:33:58 pm
content: Dear All,I was wondering if anybody made it to a next stage and actually made a real PCB of a current injector and did some measurements.@Wolfgang, your remarks are pertinent and I wondered if you had the time and courage to improve the design?Looking forward to continue reading!Peter

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 15, 2021, 06:16:15 pm
content: Peter_Clements,Welcome to the forum.I never built the circuit that I simulated in this thread. I did build and test a similar device in this thread:https://www.eevblog.com/forum/projects/high-bandwidth-current-injector-for-impedance-measurements/Regards,Jay_Diddy_B

author: Wolfgang
author_rank: Super Contributor
timestamp: September 15, 2021, 10:05:25 pm
content: Hi Peter,I confess I did not do a lot in the field of power supply impedance measurement lately. The reasons are:- finished my PhD in the field of precision oscillators and this consumed a lot of time- For the PSUs I have, my injectors worked fine. I mostly work with low noise linear stuff.- Making superfast, high amperage injectors is only possible with a bag of special tricks and components.With my old eyes and shaky hands, I leave the development of these for the pros with appropriate manufacturing capabilities.- If you have a specific question just ask. I try to answer as good is I know.Best regardsWolfgang

author: Peter_Clements
author_rank: Newbie
timestamp: September 17, 2021, 07:17:23 am
content: Thank you all for the information!

author: gailulun
author_rank: Contributor
timestamp: March 08, 2024, 03:17:10 pm
content: Thank you so much for the teardown information! Did you get pictures of other picotest modules?

author: Wolfgang
author_rank: Super Contributor
timestamp: March 08, 2024, 03:58:47 pm
content: Unfortunately no. I just have the injector. But I can only recommend to look inside their modules.They are always good for some surprises

author: amar87
author_rank: Regular Contributor
timestamp: August 28, 2025, 06:53:54 pm
content: Dear forum,I had some time on my hands and i decided to build 2 of the circuits presented here. I also made them so they fit in a hammond case and made pcb front panels. However i messed up the labeling (opps)Here are some pictures :This design(single mosfet) of the PSRR injector is not the best in my opinion because of the voltage drop. I will play around next with the design proposed by Jay in another thread where he builds a PSRR injector with 1V Vds drop. The Vds drop can be compensated for using a PSU with remote sense however there is still the increased power dissipation in the mosfet. With the design from Jay there is the disadvantage that it needs a battery.If anyone interested i will measure the frequency response but i never did this, have to figure out how to do it. For the DC bias injector I also did not take into account the lambda/4 issue that Jay pointed out i had that in my mind but unfortunately not during the layout.Phil from Phil's lab has in one of his videos an implementation which i find nice of the DC bias injector.I want to correct my mistakes and if someone interested i can share the design files i made in Altium.I ordered the boards at JLC.

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: August 31, 2025, 06:44:01 pm
content: Glad people still look at this thread. If I happen to come across other Picotest injectors, I will be sure to crack them open.If anyone has a project, you could ask Picotest for a demo to be sent to you. Of course, you'll risk breaking those silly stickers that are meant to scare you away from opening up the equipment.In regards to a demo, I was able to ask for one and I was able to get my hands on the J2111A again. There was a little rework as they added a heatsink over the opamp, but the op-amp used in the demo I received was an Analog Devices AD8065 FastFET opamp.

author: amar87
author_rank: Regular Contributor
timestamp: August 31, 2025, 07:19:43 pm
content: i don't think you ever posted pictures of the J2111A. It would be interesting to look at.I will also have some questions about this stability story but i need to study some stuff first. But right of the bat I don't get something. So i make my bode plot. the i find out that i have a phase margin of more than say 45 degree atX kHzand load transients with frequencies greater thanX kHzwill make my psu oscillate so far all good. So how does this tell me if my psu is suitable for a particular application or not ? If another psu will have more than 45 at X + 50 Khz is it better or worse. Nobody explains clearly what the crossover frequency needs to be.Or put another way. Lets say i make a universal power supply. like a phone charger or something. Where users can use it to power whatever they want. What would be the ideal crossover frequency for the bode plot in this case ?