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Picotest Injector Teardowns

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tv84:

--- Quote from: Jay_Diddy_B on May 27, 2020, 06:17:21 pm ---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.

--- End quote ---

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

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

sixtimesseven:

--- Quote from: 16bitanalogue on April 10, 2020, 12:05:00 am ---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

* 10kI 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.

--- End quote ---

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!


--- Quote from: Jay_Diddy_B on April 12, 2020, 10:58:48 am ---

LTspice model J2111A





--- End quote ---

Wolfgang:

--- Quote from: corecode on October 13, 2020, 10:02:14 am ---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 ---

LTspice model J2111A





--- End quote ---

--- End quote ---

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?

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