Output parameters of spectre for BSIM4 model lists two resistances rgbi and rgbd. Spectre Manual gives same description for both of them,'Gate Bias dependent resistance'. I am not sure what these resistance are? are thse Gate resistances? Please clarify.
The documentation doesn't give the same description (at least not in the MMSIM11.1 docs; I didn't look in older versions). rgbi is the Gate Bias-independent resistance, and rgbd is the Gate Bias-dependent resistance. There is a link to the relevant equation for the rgbd parameter. Note that rgbi is an "Output Parameter" - it's purely a function of the input parameters, whereas rgbd is an "Operating Point Parameter", since it's a function of the bias too (as the name suggests).
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.
Probably - I don't really have the time to do the full research - if this is important to you, I suggest checking a later version of the documentation, or logging a service request with customer support.