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Does anyone know a good way to convert -5/0 volt logic to 0/5 volt? I'm using a chip as seen in the diagram below, but I'm not sure what to do about the inverted logic levels. Basically, I need to add 5 volts to both logic levels to fix it (-5 volt goes to 0, 0 volts goes to 5). I know I can do the level shifting with some MOSFETs, but I'm space limited on the board so it would be really helpful if anyone could recommend an IC to do the conversion. If there is no such IC, what would be the best discrete circuit to do the conversion?

Thanks.

enter image description here

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    \$\begingroup\$ How fast are you running the data lines at? \$\endgroup\$ – ThreePhaseEel Jan 5 '16 at 1:10
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    \$\begingroup\$ Replace the -5V symbols with ground symbols, and the ground symbols with 5V symbols. Tada! \$\endgroup\$ – Matt Young Jan 5 '16 at 1:10
  • \$\begingroup\$ Also, just how much real estate do you have to play with here? \$\endgroup\$ – ThreePhaseEel Jan 5 '16 at 1:10
  • \$\begingroup\$ @matt-young ; The schematics was copied from ADN8810's datasheet, labeled "Driving Common Anode to Ground Laser Diodes with a Negative Supply" \$\endgroup\$ – TEMLIB Jan 5 '16 at 1:13
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    \$\begingroup\$ Related question: Translating to “below ground” logic levels Note the transistor array mentioned in my answer lets you pack a bunch of discretes in a tiny space. \$\endgroup\$ – The Photon Jan 5 '16 at 1:34
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You could try digital isolators :

enter image description here

http://www.analog.com/en/products/interface-isolation/isolation/quad-channel-standard-isolators/adum240e.html

http://www.ti.com/lit/ds/symlink/iso7840.pdf

Not very small, and probably more expensive than discrete transistors.

There are dozens of references.

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  • \$\begingroup\$ Yep, or optocouplers if there is room. The digital isolator is probably smaller but harder to buy. \$\endgroup\$ – William Brodie-Tyrrell Jan 5 '16 at 1:42
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    \$\begingroup\$ @TEMLIB: That's interesting, I've never worked with digital isolators. Cost isn't really a killer for me. I had considered optocouplers, but board space was a problem. \$\endgroup\$ – Alexandra Ellis Jan 5 '16 at 2:02
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If you want something that could be done using "jellybean"-ish op amps and resistors, one idea would be to use a summing circuit as a level shifter, like so, repeated for each signal:

schematic

simulate this circuit – Schematic created using CircuitLab

The resistor values shown are examples, and the AD822 can be replaced by any RRIO op amp. This doesn't provide any isolation, and requires both the +5V and -5V supplies to share a common ground, though -- I'm not sure if that's a + or a - in your application.

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