Thanks Andrew. I dont see the link which gives the equationf for rgbi and rgbd (I checked Spectre Circuit Simulator Device Model equation manual, probably I have old one). I just want to confirm with you following things
1. rgbi is nothing but Rgeltd (bias independent gate resistance) described in BSIM4 manual and is given by
Rgeltd= ( RSHG.(XGW+Weff/3*NGCON)) /NGCON*(Ldrawn-XGL)*NF
2. rgbd is nothing but Intrinsic Input Resistance (IIR) (bias dependent gate resistance which is actually channel resistance) descried in BSIM4 manual and is given by
1/Rii= XRCRG1*(Ids/Vdseff+XRCRG2* Weff*ueff*Coxeff*Kb*T/q*Leff)
Please let me know.