Differential LNA using top-biased current source?

Dear all,

I have seen much of the typical differential LNA using bottom-biased NMOS current source. Actually, could I use the same structure of the differential LNA, and using top-biased PMOS current source instead? It is because I do not seen this configuration before.
Actually, I have seen some VCO design. It could use the top-biased or bottom-biased current source with same architecture.

Thanks for your helping

wccheng