@mliberty I have been deeply involved with my ctxLink product for a while, however, I couldn’t let another opportunity to endorse Joulescope, I LOVE it.
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I just had a good long chat last week with Jerry Mendez (our local sales guy) and Tim Paasch-Colberg who is a product manager at Rohde & Schwarz.
He was showing me a rather cool T&M thing that they are currently developing for exactly this application. Basically the fact that their battery powered RTH scopes are completely floating and isolated but share the same super nice front end as their higher end scopes means you can get a really nice quiet signal down in the very very small signal range . Practically this enables using very small current shunts and still having the ability to measure both low power sleep currents as well as higher wake currents without the current shunt voltage browning out the device . They showed a slides of prototype that was very very impressive in this respect with regards to both it’s dynamic range and it’s bandwidth (hundreds of megahertz) . I’ll bug them and see if there’s an app note I can share 
it was pretty impressive and we are working on getting one in house to test
Sounds like a competitor for the Keysight CX3300 family, arguably the leader in this space. (If you have to ask how much it costs, you can’t afford it.)
But the real question is how much bandwidth do you need? If you are measuring current directly into an IC without any bypass capacitance, you can make use of this large measurement bandwidth.
If you are measuring the current to a target circuit board, not so much. You have the impedance from your power supply, cables/wires, and any connectors. If you do a very good job with very short wires and super low-impedance supply, this could be 2.5mΩ in each direction, + and -. With even just 10 µF bypass capacitance on your board, your target board bandwidth is:
1 / (2 * π * 5e-3 Ω * 10e-6 µF) = 3 MHz.
Most typical lab setups with banana jacks and 3’ of wires will be closer to 50 mΩ. Banana jacks have 1 mΩ connector resistance. 18 AWG is 6.3 mΩ/ft.
4 connectors + 6 ' of 18 AWG = 4 * 1 mΩ + 6.3 mΩ/ft * 6 ft = 42 mΩ
With this setup, you only get 379 kHz of system bandwidth. Coincidentally, this is how I determined the design objective for Joulescope’s target bandwith. Joulescope uses a 10 mΩ shunt in its highest current range setting. Other impedances (Joulescope’s MOSFET, PCB traces, the internal front-panel connector and the external connectors) add another ~15 mΩ. So, with 2 sets of 1’ banana wires (Joulescope sits between your power supply and target board), the system input resistance is:
4 connectors * 1 mΩ + 4' * 6.3 mΩ + 25 mΩ = 54.2 mΩ
This setup with 10 µF target bypass capacitance gives 294 kHz which is slightly higher than Joulescope’s 250 kHz bandwidth specification, but that spec is a conservative number.
Note that I am intentionally leaving out the supply impedance. A small LiPo battery can easily add 100s of mΩ.
So, if you want to measure current to a target board, save your $$$ and buy a Joulescope 
. Joulescope’s sensor inputs are electrically isolated, up autorange in 1 µs (no target brown-out), and measure 32-bits of effective range.
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Hi Matt, I finally got some spare money and ordered a Joulescope too! Hopefully the customs here won’t ruin my day with it, like they did with a LiDAR module a couple of days ago… 
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Awesome and thank you! If your customs office requests any additional information, DM me! Hope your Joulescope travels quickly and safely! 
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Excellent! I hope your Joulescope serves you well for many years. If you have any questions or issues, DM me, or post over on the Joulescope forum.
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I was playing with the Joulescope (@mliberty you are a spell! ) today measuring current consumption of my latest IoT product which has 2G/NBIoT and M1 connectivity.
Strangle enough I need to measure the current consumption in the worst case scenario which is when the device is notable to connect to the network…and keeps polling the network for a while…
Any suggestion for bench Farady cage or something that will act as shield?
Did try with foil but didn’t work…I must live very close to a cell tower…
Thanks!
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Metal garbage can with tight fitting lid is one cheap option
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Stick a 50 ohm resistor on the uFL connector?
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I’ve seen a few Linear Tech/Analog Devices app notes that use decorative metal cookie tins for this purpose.
Not a bad excuse for buying some cookies, either. 
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It has a discrete antenna on board, and being the only sample I have I would try to avoid desolder it…
If you want to go fancy, they make manual RF shield boxes with cable holes. I picked one up for super cheap at an auction a few years back, it’s pretty handy. Definitely would’ve used a trash can if I had to pay full price though. Like this:
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At day job we’ve used a full spectrum from cookie jars to garbage cans to actual shielded boxes. I managed to pick on of the latter at a Hamfest for $40 . Saelig sells Ramsey ones as one example: http://www.saelig.com/category/MFR00066.htm?Screen=CTGY&Category_code=ramsey-faraday-enclosures
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During a past life, we used faraday bags/pouches to keep devices from connecting to towers and routers during transport. Since they are flexible pouches, they may not meet your lab test setup, but it’s a nice piece of kit to know about. As we move towards more connectivity, there are bound to be more times that we want to prevent it. They’re all fairly similar but the “mission darkness” line was the go-to brand. They could be better, they could just have better marketing, but they are well accepted in the digital forensics communities.
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Aren’t we headed toward that time of the year for biscuits in giants tins from Costco?
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Cookie tins are nice. I built a pair of these for isolating RF devices . note the SMA connectors and EMI feed through devices.
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I am working on a power analyzer, more for fun, than a coming product (all though I hope it turns into a product)
@mliberty: How do you handle the temperature drift of the RDSon of the shunt FETs. For the 1A range, you will probably be using a sub 5mOhm FET, and I think one review talked about a 10mOhm sense resistor. So, the best way is just to calibrate out the terminal resistances, FET resistance and shunt.
But, when the FET resistance has 30% of the voltage developed and increases to 50% more resistance at high temperature, it will show up as an error.
One way to solve it is to have seperate sense points for each sense resistor, before the shunt FET, so the FET is out of the equation. Then you need a mux to bring those signals in
Joulescope does not include the voltage drop across the MOSFETs in the shunt resistor voltage measurement. It only measures the voltage across the shunt resistor(s), and very carefully. Layout matters. Carefully qualifying the RDSon of a MOSFET across components, over temperature, and over aging is asking for pain.
Yes, I was thinking it would be difficult with the FET in the loop. That’s the reason for the comment about needing a Mux
The mux is low cost anyway, so no reason to ask for trouble 