Re: Series MOSFET model

Stephen:

At this time, I would pretend that this is still an n-FET
device and use Vgs based on the "Vcc" node. However, the
setup and measurements would be for both the n-FET and p-FET
devices in parallel.

Bob Ross
Mentor Graphics

Stephen Nolan wrote:
>
> IBIS experts, please help with another question. When making an IBIS model of a
> FET switch, the IBIS spec calls for the following model:
>
> | The model is:
> |
> | Table Current
> | ------->
> | + Vds -
> | Pin 1 Pin 2
> | <---| |---> +
> | d |_____| - s
> | --+-- Vgs Vs
> | | g +
> | -
> |
> | Vg = [Voltage Range] = Vcc
> | Vgs = Table Voltage = Vtable = Vcc - Vs
> | Ids = Table Current for a given Vcc and Vds
>
> The table voltage that is reported is Vgs, the voltage difference between pin 2
> (in this example) and the gate voltage (usually Vcc). This is an entirely
> adequate model for n-FET only series switches, however several FET switch
> devices use a full transmission-gate (n-FET in parallel with p-FET). When the
> switch is enabled [On] the gate of the n-FET is usually at Vcc and the gate of
> the p-FET is usually at ground.
>
> GND
> |
> o
> =====
> | | p-FET
> --| |--
> | |
> ----+-| |-+----
> |_____| n-FET
> --+--
> |
> Vcc
>
> The question, obviously is "Which Vgs do I report in the table?"
>
> --
> Regards,
> Stephen M. Nolan
Received on Thu Jul 20 17:22:19 2000