Hi,

without knowing your design it is hard to specify its power supply. Ripple requirements depend on your circuit's PSRR (power supply rejection ratio) and its frequency dependency. Power supply definition also depends on the current consumption of your chip.

Notice that most commercial power supplies are switched power supplies, which usually exhibit ripple at a particular frequency (switching frequency). For low ripple, you should use a low drop-out regulator (LDO) between the switched supply and your chip.

You can certainly find a lot of useful information in the appnotes of commercial LDO vendors (Analog Devices, Linear Technology, Maxim and many others I may forget).

I hope this helps a little

Paul