the bsim-3 spice model

The third version of BSIM (Berkeley short channel IGFET model).

The BSIM-3 model was developed for submicron devices.

It has approximately 120 parameter , each having physical significance .

The main difference of BSIM-3 from BSIM-1 is that

the effect of noise and temperature taking into account .

The drain current and its first derivatives are continuous over all region of operation, which helps the convergence problem.

The threshold voltage is determined using

VTHN = long channel threshold voltage. PHI = surface potential. = threshold voltage reduction due to

short channel effect. K1,K2 = vertical non- uniform doping effect.

The threshold voltage model

Xd = The depletion width between the channel and substrate.

Xd /n = average depletion width along the channel.

DVTHN0 , DVT1, and n can be determined from

experimental data .

The operating region of BSIM-3 are divided in to three categories.

1. strong inversion :---> VGS > VTHN

2. Weak inversion :----> VGS < VTHN

3. Transition region:----> VGS = VTHN

The strong inversion region is again subdivided in two region

1. Triode region --> VDS < VDS SAT

2. Saturation region --> VDS > VDS SAT

The drain current in the saturation region is given by

VA = early voltage generated by MOSFET output generated by output resistance.

The drain current in the triode(linear) region is given by,

drain current in the weak inversion or sub threshold region is given by,

Voff = offset voltage

n = sub threshold slope parameter.

Major frustration using BSIM model is convergence.

Parameters to be adjusted

1. ABSTOL -- the default value is 1 pA.

2. VNTOL -- the default value is 1 uV

3. RELTOL -- the default value is 0.001 Increasing the values of all three parameters helps

speed up the simulation and assists with convergence problem at the price of reduced accuracy.

To help with the convergence following statement can be added in to SPICE Netlist.

The N channel MOSFET equations.

THANKS……… Dhaval… P08EC904