Re: What determines Vref & Rref, R_fixture & V_fixture?

Greg,

If the standard delay test for your part requires only
a capacitive load, then give C_ref but omit R_ref and
V_ref. Use the latter only if the buffer must be tested
with a pullup or pulldown resistor. You will have to
choose just one capacitive load to give as C_ref. But
this should be the load that was used to make measurements
that went into the timing info for the part.

R_fixture and V_fixture have been discussed before on this
list, but I think the best advice (from Stephen Peters)
was to consult the latest IBIS Cookbook linked from:

  http://www.eigroup.org/ibis/tools.htm

You will not find "R_fixture" in there, but Table 1 gives
recommended values for waveform fixtures.

Mike LaBonte

Greg Haynes wrote:
>
> I'm starting to use s2ibis2 to create models
> for a gate array library. I don't understand
> the significance of the Rref and Vref sub-parameters
> under [Model]. We characterize propagation delays
> for the I/O buffers in SPICE for a range of
> capacitive loads on the output pad. It isn't
> clear what values to use for Rref and Vref
> (or Cref for that matter).
>
> Similarly, how do I determine the values to
> use for R_fixture and V_fixture with
> [Rising Waveform] and [Falling Waveform]?
>
> -Greg Haynes
> UTMC
 
Received on Sat Feb 24 12:11:29 2001