I want to create a Spice model for the AFM906N to simulate an application in the band of 30MHz.
I need the folloeing information:
The parameters needed to define a MOSFET in LTspice are as follows:
Rg Gate ohmic resistance
Rd Drain ohmic resistance (this is NOT the RDSon, but the resistance of the bond wire)
Rs Source ohmic resistance.
Vto Zero-bias threshold voltage.
Kp – Transconductance coefficient
Lambda Change in drain current with Vds
Cgdmax Maximum gate to drain capacitance.
Cgdmin Minimum gate to drain capacitance.
Cgs Gate to source capacitance.
Cjo Parasitic diode capacitance.
Is Parasitic diode saturation current.
Rb Body diode resistance.
Rg, Rd and Rs are the resistances of the bond wires connecting the die to the package.
Vto is the turn on voltage of the MOSFET.
Kp is the transconductance of the MOSFET. This determines the drain current that flows for a given gate source voltage.
Lambda is the change in drain current with drain source voltage and is used with Kp to determine the RDSon.
Cgdmax and Cgdmin are the minimum and maximum values of the gate drain capacitance and are normally graphed in the MOSFET datasheet as Crss. The capacitance of a capacitor is inversely proportional to the distance between its plates. When the MOSFET is turned on, distance between the gate and the conducting channel of the drain is equal to the thickness of the insulating gate oxide layer (which is small) so the gate drain capacitance is high. When the MOSFET is turned off, the gate drain region is large, making the gate drain capacitance low. This can be seen on the plot of Crss.
Cgs is the gate source capacitance. Although it changes slightly with gate source voltage, LTspice assumes it is constant.
Is is the parasitic body diode saturation current.
Rb is the series resistance of the body diode.
The datasheet does not give this information.
Thanks in advance for some help
Herbert
