Electronics > Metrology

Measuring nanoamps and below like a Ninja

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MrYakimovYA:
Ok, USB is good) I'm also developing my highly precision and highly unabtanium device (picoammeter/voltage source). And now I'm thinking about connection interface. Ethernet based on W5500 (Aliexpress have low prices again) looks very very very attractive.
It has:
1. Built-in galvanic isolation.
2. Standard connectors and network structure.
3. Allows to have console (one socket) and up to several data stream (the other sockets).
4. May be the LXI can be added (I don't know about license).
5. W5500 (Wizner) give you hardare TCP/IP stack.

Don't you thing about such solution?)

shodan@micron:

--- Quote from: MrYakimovYA on August 18, 2022, 06:26:35 am --- I'm also developing my highly

--- End quote ---
Good luck!


--- Quote from: MrYakimovYA on August 18, 2022, 06:26:35 am ---Don't you thing about such solution?)
--- End quote ---
If you want sell your solution it reasonable.

shodan@micron:
My completely illegal's, sanctioned refs will be delivered soon... So... it's time to start thinking about new Low-Noise, Mirror-free reference concept...
Earlier version use R+R mirror for making -7V reference for DAC, but i want try new mirror-free concept to do not amplified noise and instability. :popcorn:

Kleinstein:

--- Quote from: shodan@micron on September 02, 2022, 04:48:18 am ---My completely illegal's, sanctioned refs will be delivered soon... So... it's time to start thinking about new Low-Noise, Mirror-free reference concept...
Earlier version use R+R mirror for making -7V reference for DAC, but i want try new mirror-free concept to do not amplified noise and instability. :popcorn:



--- End quote ---

Using separate references for the positive and negative side is a 2 sided thing. It avoids the inverter, but it also means that at zero output there is noise from both references and not the usually lower noise of the inverter.  For most uses I would consider the inverter the smaller evil.  One could still build the reference in a way to relatively easy switch between the 2 separate references and a more inverter like version:  the inverter like version would have the point between the 2 references not connected to AGND, but driven by an OP-amp to force the average of the 2 outputs to be at AGND. Functionally this is essentially the same as the inverter version, just a little more symetric.

With the extra buffers for the references, one could consider some easy to add RC fitlering for the references.

The reference amplification to provide the reference current should not use AZ OP-amps like the OPA189. There is no real need for them and they can do more harm than good from EMI and possible beating. So I would prefer something like OP07 or a more modern (and lower power) OPA202. In theroy even an LM358/RC4552 could do.

shodan@micron:
Maybe you're right about noise, i'm think about it. :-/O

But my research shows RFB+RCM+ROFS buit-in DAC R+R network is have terrible instability and big tempco.
Positive +7V reference rail into old concept is rock solid. But negative -7V reference rail which the produced by buit-in DAC R+R is drifting so much... need a many hours to stabilize it after turn on the device.
Also datasheet shows typical tempco of internal R+R network is ±0.04 ppm FSR/°C, but i see much higher tempco. Use external Z-Foil R+R maybe is better way, but i cant check it in near future.
So... i don't want use buit-in DAC R+R network anymore... therefore i'm try search concept without R+R networks.

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