Re: [SI-LIST] : HSTL voltage levels

D. C. Sessions (dc.sessions@vlsi.com)
Wed, 04 Aug 1999 09:25:12 -0700

Hansel Collins wrote:

> As for Vol and Voh, they would normally swing GND to VDDQ or 1.5V. The JEDEC
> specification specify a maximum output low of Vol= 0.4V (DC) and minimum Voh
> = Vddq-0.4V.

Remember that these are loaded values *+/- 8mA for class I) and effectively
specify output drive strength (nominal max Rs=50 ohms) In a non-shunt-terminated
application a the practical values are 0 and Vddq

> This yields worse case noise margins of 180mV (Vil to Vol DC)
> and 80mV(Vil to Vol AC). For the high state a noise margin of 220mV (Vih to
> Voh DC) and 120mV (Vih to Voh AC).

Watch out -- noise margin to the AC numbers is irrelevant. The AC thresholds
are guaranteed to cause a change of state, but for noise margin you only care
about the DC thresholds; they are the limits of what is guaranteed to NOT
cause a change of state.

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

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