> From: John V
> Sent: Thursday, September 25, 1997 8:55 AM
> To: Signal Integrity Mailing List
> Cc: email@example.com
> Subject: [SI-LIST] : SSO noise: Through current vs. Discharge
> Several weeks ago I asked a question to the list concerning
> simultaneous switching noise (SSN). I received many useful
> answers. Most pointed me towards Senthinathan and Prince,
> which I have ordered, but not yet received.
> One issue that concerned me was the influence of load
> capacitance on the SSN. The answer, it seems, depends on
> the design of the output buffer:
> 1) If the P and N transistors are momentarily ON,
> then the "through" current dominates, which means that
> the maximum noise amplitude is independent of the load.
> This is because the di/dt of the through current is greater
> than the di/dt of any (dis-)charge current.
> 2) If the output buffer is designed so that the P and N
> buffers are never both ON, then the SSN source
> is predominately the (dis)charge current. SSN increases
> with Cload up to a certain value of Cload, then plateaus
> off (Vmax).
> If the Cload is replaced by a transmission line, then
> then a simple rule is that the SSN is (Iz/Isc)*Vmax,
> where Isc is the short-circuit output current and Iz is the
> output current for a resistance equal to the impedance of
> the line.
> This interpretation prompts the following question:
> Are real-life buffers designed such that the P and N
> transistors are never ON simultaneously?
> John Fitzpatrick <John.Fitzpatrick@ln.cit.alcatel.fr>
> Alcatel Telecom, 4 rue de Broglie, 22304 Lannion, France
> Tel: +33(0)2.96.04.79.33 Fax: +33(0)2.96.04.85.09