Half rate OR Full rate PD FOR CDR

i have to design 4 GBPS CDR in 65nm technology...according to the area requirement i have to go for ring oscillator. please anyone can suggest whether i should go for a half rate or full rate PD...& Give the reason too why should...
Thanks in advance

Please give me detail about it. I don't understand about it.

sir,
i have area constraint on the design. So i cannot use LC VCO. I have to go for a ring oscillator. I am in a confusion whether i have to use fullrate or halfrate phase detector to be used in CLOCK DATA RECOVERY SYSTEM. can u suggest me which phase detector i have to use?