-5/0 volt to 0/5 volt logic levels?

Question

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.

Answer 1

You could try digital isolators :

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.

Answer 2

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:

^{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.