Picotest Injector Teardowns

[16bitanalogue]

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 Injector
Price: $525
BOM:

(4) Capacitors

• C1||C2 = 35.7uF
• C3||C4 = 1.98uF

(1) Resistor

• 10k

(1) nMOS

• AOT2618 from Alpha and Omega Semiconductor, http://www.aosmd.com/res/data_sheets/AOT2618L.pdf

J2120A front and rear pics attached.

Picotest J2130A DC Bias Injector
Price: $525
BOM:

(24) Capacitors

• Parallel, Series network = 27uF

(1) Resistor

• 10k

I 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 Transformer
No 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.

[Sighound36]

Hello 16Bitanalogue

This was going to be a couple of my next purchases much appreciated.

[Jay_Diddy_B]

16bitanalogue,

Thank you for the teardown pictures and welcome to the group.

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 Injector
Price: $525
BOM:

(4) Capacitors

• C1||C2 = 35.7uF
• C3||C4 = 1.98uF

(1) Resistor

• 10k

(1) nMOS

• AOT2618 from Alpha and Omega Semiconductor, http://www.aosmd.com/res/data_sheets/AOT2618L.pdf

J2120A front and rear pics attached.

Snip ...

I hope this comes out clean, first time poster. Hell of a time with the pics.

You 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

[fcb]

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.

[16bitanalogue]

You 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.

I 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.

[Jay_Diddy_B]

Hi group,

Here is the J2120A schematic:




Regards,

Jay_Diddy_B

[16bitanalogue]

Picotest J2112A High Current Injector
Price: $1,995
BOM:
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.

[Jay_Diddy_B]

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

[Jay_Diddy_B]

Picotest J2112A High Current Injector
Price: $1,995
BOM:
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.

This looks like this:




This is basically a current sink that can work with either positive or negative inputs:

Regards,

Jay_Diddy_B

[Jay_Diddy_B]

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.pdf

LTspice Model




This is using one of the op-amps available in LTspice.

Simulation Results




I have attached the LTspice model.

Regards,
Jay_Diddy_B

[16bitanalogue]

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.

[Sighound36]

Thanks for all your efforts chaps first class.

Howabout a group design and build?

[2N3055]

Fantastic topic!! Great work here!!

[Ribster]

I can design and assemble some boards if you guys are interested..

[Sighound36]

More than happy with that thank you

[Jay_Diddy_B]

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

[Sighound36]

Hi Jay_Diddy_B

Thank 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

[_Wim_]

I can design and assemble some boards if you guys are interested..

I am also interested in these! 

[Jay_Diddy_B]

Picotest J2112A High Current Injector
Price: $1,995
BOM:
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.

The pictures that were included are actually the J2111A

I 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 J2111A




And the modelling results:



I have attached the LTspice model.

Regards,
Jay_Diddy_B
 J2111A concept model.asc (5.46 kB - downloaded 120 times.)

[Jay_Diddy_B]

Hi Jay_Diddy_B

Thank 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

Hi,

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 100mm

The plan is to use Keystone 575-4 for the connections.

Comments?

Jay_Diddy_B

[16bitanalogue]

Picotest J2112A High Current Injector
Price: $1,995
BOM:
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.

The pictures that were included are actually the J2111A

I was having difficulty getting the component values, that I can read in the photograph, in the model agree with the datasheet performance.

Oops! 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.

[16bitanalogue]

The board is 100mm x 100mm

The plan is to use Keystone 575-4 for the connections.

Comments?

Jay_Diddy_B

I 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.

[Wolfgang]

Picotest J2112A High Current Injector
Price: $1,995
BOM:
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.

The pictures that were included are actually the J2111A

I was having difficulty getting the component values, that I can read in the photograph, in the model agree with the datasheet performance.

Oops! 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.

When 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 keep
  this spec, you need better transistors and better cooling.

[Jay_Diddy_B]

When 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 keep
  this spec, you need better transistors and better cooling.

Wolfgang,

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

[Jay_Diddy_B]

Hi,

Further to my last reply, the manual that can be found here:

https://www.picotest.com/support.html

On page 44 it says the maximum input voltage is DC +  AC is 5V

5V x 74mA = 375mW

This is consistent with the transistor selection and mounting method.

Regards,
Jay_Diddy_B

[Sighound36]

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

[Jay_Diddy_B]

Hi,

Some good investigational work there chaps.

Personally if going to this detail I would rather over engineer the whole thing using much better specifications on not just the parts but the board and box. My personal thoughts

I would be interested to know from users of the PicoTest  injectors which ones are really useful and what improvements are desirable.

I have built and used:

1) Injection transformer for loop measurements - many times

2) PSRR measurement device - Occasionally only with high performance LDOs

3) 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

[Sighound36]

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

[Wolfgang]

Hi,

Further to my last reply, the manual that can be found here:

https://www.picotest.com/support.html

On page 44 it says the maximum input voltage is DC +  AC is 5V

5V x 74mA = 375mW

This is consistent with the transistor selection and mounting method.

Regards,
Jay_Diddy_B

In my J2111A manual the *output* voltage (and its not the input voltage that counts here) is 40V. So the power is way too much.

[Jay_Diddy_B]

Hi,

Further to my last reply, the manual that can be found here:

https://www.picotest.com/support.html

On page 44 it says the maximum input voltage is DC +  AC is 5V

5V x 74mA = 375mW

This is consistent with the transistor selection and mounting method.

Regards,
Jay_Diddy_B

In my J2111A manual the *output* voltage (and its not the input voltage that counts here) is 40V. So the power is way too much.

Wolfgang,

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

[Wolfgang]

Hi,

Further to my last reply, the manual that can be found here:

https://www.picotest.com/support.html

On page 44 it says the maximum input voltage is DC +  AC is 5V

5V x 74mA = 375mW

This is consistent with the transistor selection and mounting method.

Regards,
Jay_Diddy_B

In my J2111A manual the *output* voltage (and its not the input voltage that counts here) is 40V. So the power is way too much.

Wolfgang,

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

Hi,

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* wiring
between 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.

Regards
  Wolfgang DL1DWG

[16bitanalogue]

Hi,

Some good investigational work there chaps.

Personally if going to this detail I would rather over engineer the whole thing using much better specifications on not just the parts but the board and box. My personal thoughts

I would be interested to know from users of the PicoTest  injectors which ones are really useful and what improvements are desirable.

Regards,
Jay_Diddy_B

Even 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.

[Sighound36]

You could try a BDX33C and use a heat-sink that handles up to 5amps no problem BW is sufficient to.

[Jay_Diddy_B]

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

[Wolfgang]

Is this a bias Tee ? Where is the decoupling inductor ?

[Jay_Diddy_B]

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

[Sighound36]

Yes I am interested Jay thank you

[Jay_Diddy_B]

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

[Wolfgang]

... what does your VNA say to this one ?
... how much current does the inductor tolerate before saturating ?

[Jay_Diddy_B]

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

[Wolfgang]

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 to
set 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.

regards
  Wolfgang

[Jay_Diddy_B]

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

[Sighound36]

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?

Thanks

Sighound

[free_electron]

why dont you combine several of these into 1 unit ? or make a 'breakable' circuit board.

[Wolfgang]

@ to all
The art of bias tees is complex because all elements (series Cs, Ls, ...) have parasitics
and 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 DC
resistance, 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 voltage
regulators 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, ...).

regards
  Wolfgang

[sixtimesseven]

Hi group,

been busy with KiCAD and Fusion 360.

Any interest in this project:

(Attachment Link)

(Attachment Link)

This is a blocking capacitor and bias injector.

Regards,
Jay_Diddy_B

Yes, 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

[Jay_Diddy_B]

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 100mm

0 - 200MHz



A 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 VNA

0 - 1.5GHz

The frequency range was widened to 1.5 GHz



There is a notch at 922MHz

After 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 625MHz

This notch is when the open length of the line is 1/4 of wavelength.

3 x 10E8 /625 x 10E6  = 48cm

1/4 wavelength = 12cm

velocity factor = 0.66

It kind of works out.


At 922MHz

wavelength = 3 x 10E8 / 922 x10E6 = 32cm

quarter wavelength = 8cm

Open circuit transmission line



The resistor needs to be moved closer to the capacitors.

Regards,
Jay_Diddy_B

[Jay_Diddy_B]

Hi,

The bias line was cut in this location:



And the measurement repeated:



Same vertical scale 5dB/div

Considerable improvement.

Some of the other 'wiggles' will go away if I have more vias between the top and bottom planes.

Regards,
Jay_Diddy_B

[Sighound36]

Hi Jay

As with all things RF, some of the smallest movements generator some of the most obvious gains.

Great work 

[Jay_Diddy_B]

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 Design





Prototype board





The board was made from 0.062 FR4 on my LPKF Protomat c60.

Board Assembly





I inserted some of the 'via wires'

Measurement

I used an HP 8714 for the measurement:



This is 3mHz to 3GHz 2dB/div.

looking good!!

Jay_Diddy_B

[Sighound36]

Pretty respectable trace there for a 3Ghz bandwidth 

Ok 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?

[Jay_Diddy_B]

Pretty respectable trace there for a 3Ghz bandwidth 

Ok 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 fot he design?

The 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 = 60uF

R= 25

F = 1/(2  x Pi x R x C) = 26.5 Hz

Regards,
Jay_Diddy_B

[Jay_Diddy_B]

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 50 cables:





From left to right

The 50 Ohm cable
the 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 are
50 Ohm track
SMA connector
50 Ohm cable


I 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

[Sighound36]

In a very crude way that is the situation I was attempting to elude to 

Great stuff Jay, really do not know where you find the time but top man 

[2N3055]

Nice demonstration of usefulness of TDR..

Great work (as always!!) Jay..

Regards,

Sinisa

[tv84]

I have marked the measured impedances on this drawing of the board assembly:

(Attachment Link)

to raise the impedance where the capacitor are, I need to widen the gap between the traces and the ground plane.

Damn! This is an optimization of my suggested change!!!        Respect!

(I had removed it because, afterwards, I thought it was something irrelevant... )

[sixtimesseven]

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 Injector
Price: $525
BOM:

(4) Capacitors

• C1||C2 = 35.7uF
• C3||C4 = 1.98uF

(1) Resistor

• 10k

(1) nMOS

• AOT2618 from Alpha and Omega Semiconductor, http://www.aosmd.com/res/data_sheets/AOT2618L.pdf

J2120A front and rear pics attached.

Picotest J2130A DC Bias Injector
Price: $525
BOM:

(24) Capacitors

• Parallel, Series network = 27uF

(1) Resistor

• 10k

I 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 Transformer
No 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.

Another 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.

[corecode]

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!

LTspice model J2111A

[Wolfgang]

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!

LTspice model J2111A

R1, 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/

[corecode]

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?

[Wolfgang]

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 !

[corecode]

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.

[corecode]

I will simulate various DUT impedance configurations next.

Doesn't look too bad - of course the wiring to the DUT has a huge impact at the high frequencies.

[Wolfgang]

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.

[corecode]

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.

[Wolfgang]

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.

[Peter_Clements]

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

[Jay_Diddy_B]

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

[Wolfgang]

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 regards
  Wolfgang

[Peter_Clements]

Thank you all for the information!

[gailulun]

Thank you so much for the teardown information! Did you get pictures of other picotest modules?

[Wolfgang]

Unfortunately no. I just have the injector. But I can only recommend to look inside their modules.
They are always good for some surprises