mixed-signal circuit power problem?

[alson]

I had designed a digital and analog circuit.analog block is a biphasic current output stimulator.it has +VCC and -VSS.
digital block had function to control stimulator.it's power is +VDD and GND

now! i wanted to use UMC 0.18 porcess fabricate.how to slove the analog and digital power problem?

 

[skyismylimit]

Give separate ground for both analog and digital separately and give the supply also from different pins... short the gnd only outside the chip

 

[ambreesh]

i hope u have twin tub process. As substrate contact for Analog is -vss and for digital it is vdd.

I am not clear what skyismylimit means by shorting the gnd pins outside. Which gnd pins are u talking about. Could u elaborate.