SE active negation output characteristics

Jeff Schroeder jeffrey.schroeder at
Fri Oct 29 13:55:56 PDT 1999

* From the T10 Reflector (t10 at, posted by:
* Jeff Schroeder <jeffrey.schroeder at>
I'm hoping somebody can help shed some light on what appears to me to be
some conflicting requirements for the single ended active negation
output characteristics.

Referencing SPI-3 rev. 10: Table 18 says, "b) Voh (high-level output
voltage) = 2,5 V D.C. to 3,7 V D.C. (signal negated). See figure 26 for
Ioh." However, figure 26 clearly shows the range to be 2.0 V to 3.7 V,
at least when the current is below 7 mA. Adding to the confusion is that
the spec in table 18 does not specify Ioh.

So, I did a little digging in the archives to see if I could find where
this originated. Revision 1 of the Fast-20 spec had four rules that
governed Voh and Ioh for active negation. Among them were these two:
  "b) Voh (high-level output voltage) = 2,5 to 3,7 V d.c. (signal
   c) Voh (high-level output voltage) = 2,0 to 3,24 V d.c. at Ioh = 7 mA
      (signal negated);"

These two rules are not necessarily in conflict, since rule c) does not
specify the current as Ioh < 7 mA, but as Ioh = 7 mA. After some
discussion and adjusting of the voltage and current values, rules c),
d), and e) were transformed into what is today figure 26 in SPI-3.
However, rule b) still persists also, and it appears to be in conflict
with figure 26, which shows the minimum Voh to be 2.0 V for all Ioh < 7

Am I missing something here? Will the real Voh requirement please stand

Jeff Schroeder
TPA Americas
STMicroelectronics, Inc., San Jose, CA
Email: jeffrey.schroeder at  Phone: 408-487-3965 Fax: 408-441-8470
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