read only positive voltage and i have low difference voltage somtimes negative

[adison]

I have difference voltage that I put into digital converter the problem is that sometimes the difference is positive and sometimes the difference is negative
If the difference is negative the digital converter can't read it
I work with low voltage approximate 10 until 20 milivolt
How I can to turn over the wires to receive positive difference ?
Are this low voltage can work with diodes bridge ?
Maybe the solution can be level shifter ?
  http://www.daycounter.com/Circuits/OpAmp-Level-Shifter/OpAmp-Level-Shifter.phtml
maybe to add more voltage ?
maybe to put the digital converter in reversed and read the digital converter that through information ?
I will glad to receive help
 

[adison]

up

[awally88]

Normal Diodes have a drop of around 0.6-0.7V over them so they can't be used, I assume you can buy some that have a lower drop but I've never looked for them sorry.

Op amp is a good idea, if you can amplify the voltage that is being put through you can then use a normal diode bridge. Keep in mind your digital converter will have to deal with this increased voltage.