Re: [SI-LIST] : Output Impedance

D. C. Sessions (dc.sessions@tempe.vlsi.com)
Wed, 01 Apr 1998 10:55:14 -0700

alaa alani wrote:

> What is the simplest way to measure the output impedance of a buffer
> given just a spice netlist?

Since CMOS buffers are generally very nonlinear, the first
problem is to decide what you mean by "output impedance."

Example: Zout is the value of pull-up resistance to Vddq
that the driver can pull down to Vddq/2

Example: Zout is the slope of the V/I curve at the supply
intercept.

Example: Zout is Zline minus the series resistance that
gives a first-incidence amplitude of Vddq/2.

For all of these the answer is pretty clear as soon as you
choose the definition; just simulate the output under the
given conditions and constraints.

-- 
D. C. Sessions
dc.sessions@tempe.vlsi.com