Re: Driver Output Impedance Calculation

> Given the ibis model data that follows, how does one determine
> the output impedance of this driver for both the pullup and
> pulldown side of the driver.

Output impedance tends to be nonlinear, but the small-signal, low
frequency impedances are easy to estimate. Just look at the slopes
of the Pulldown and Pullup curves where they intersect 0V.

> [Pullup]
> | I(typ) I(min) I(max)
...
> 0.2 -7.0m NA NA
> 0.1 -3.0m NA NA
> 0.0 -45.0p NA NA
> -0.1 3.0m NA NA

0.1V/3.0mA = 33 ohms for the pullup, immediately around VDD.

> [Pulldown]
> | I(typ) I(min) I(max)
...
> -0.1 -4.0m NA NA
> 0.0 18.0p NA NA
> 0.1 4.0m NA NA
> 0.2 8.0m NA NA
> 0.3 11.0m NA NA
> 0.4 15.0m NA NA

0.1V/4.0mA = 25 ohms for the pulldown, immediately around GND.

Use a bigger delta-V for more accuracy; it looks like the current
resolution (accuracy) in your tabulated data is 1.0mA.

Regards,
Andy Ingraham
 
Received on Thu Oct 30 09:15:25 1997