How do one bias an AC signal to a DC signal to be measure by an ADC which only accepts positive voltages?

 

A precision full wave rectifier works very well. Take your pick - http://sound.westhost.com/appnotes/an001.htm

 

rectifying the signal but not biasing? but I need to know the negative too as I need to display it in graph.

How about the microchip bipolar ADC??
http://malaysia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0403153

 

If we have the full requirement, it makes it easier to suggest a solution.

That converter should work fine, if it gives you the precision you need.

 

measuring an AC 60Hz sine wave current using a current transformer.
Need 1mV/1mA sensitivity.

 

You could use an op amp for the offset (i.e., add a DC voltage to the AC waveform).

 

I try not to use opamp as I do not have positive and negative supplies which the opamps need.

I tried using the cap followed by a voltage divider, the cut-off is at 15Hz which is well below my 60Hz, blocking the DC component. But tried it on breadboard, it stays at the same voltage no matter what AC signal i couple in. Maybe my voltmeter could not measure this correctly.