Size the following circuit so that it achieves a 100 ps delay (50-50) using 0.25 μm devices, while driving a 100 fF load on both differential outputs. (VDD = 2.5V) Assume A, B and their complements are available as inputs. Other data available for NMOS are following Vt=0.43(V),Vdsat=0.63(V),k'=115x10^-6 (A/V^2),lambda=0.06(v^-1),technology 250nm

I computed current charge/discharge Ic=C*dv/dt with C=100fF and dv/dt=(vdd/2)/T con T=100ps and Vdd=2.5V ,because current In for two nmos depends on w/l then In=Ic but I don't know how to compute current for two NMOS series,can you help me?