Products > Test Equipment
Picotest Injector Teardowns
Wolfgang:
--- Quote from: Jay_Diddy_B on April 13, 2020, 04:54:46 pm ---
--- Quote from: Wolfgang on April 13, 2020, 03:35:54 pm ---
--- Quote from: Jay_Diddy_B on April 13, 2020, 03:32:51 am ---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
--- End quote ---
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.
--- End quote ---
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
--- End quote ---
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:
--- Quote from: Jay_Diddy_B on April 13, 2020, 11:25:44 am ---Hi,
--- Quote from: Sighound36 on April 13, 2020, 10:44:40 am ---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
--- End quote ---
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
--- End quote ---
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 ?
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