Hi all,

I'm new to the analog/mixed-signal design, esp. in the sense of layout, and I just found some questions which have annoyed me these days. Any suggestions will be appreciated.

In my design, there is an opamp, which is supplied between plus/minus 3.3V, a bandgap circuit which is supplied between positive supply, Vdd,  and gnd, and some digital logic circuits also supplied between positive supply and gnd. First, I built them seperatedly and they all pass the DRC & LVS check. Then, when I tried to put the opamp and the logic together and did the DRC check, it came up with some errors saying short between Vssa and gnd! and short between Vdda and vdd!. I think the problem could be  the p-substrate/nwell contacts because I have put them to both of the two parts. My question now is
1) how to put the analog and digital circuits together when they have different power supplies and do the DRC and LVS check? what do peope usually do in this topic, and
2) would there be any concerns i should be aware of if two analog blocks using different supplies are put together (like the bandgap circuit and the opamp in this work) coz i havn't moved on to that part yet.

looking forward to your opions
Mike