**From:** sweir (*weirsp@atdial.net*)

**Date:** Mon Mar 26 2001 - 22:11:58 PST

**Next message:**Jay Diepenbrock: "[SI-LIST] : internal timestep too small in transient analysis"**Previous message:**sunil-chandra.kasanyal@st.com: "[SI-LIST] : Centre Tap Termiation"**In reply to:**ªL´Â·×: "RE: [SI-LIST] : Any standards of the derating of Capacitors,Resit ors, and inducto rs?"

John,

Yes, the derivation is pretty simple. For a series terminated driver, a

new edge passes through a divider network that consists of:

The driver, assumed zero ohms.

The series termination resistor, R,

The transmission line, assumed R matches the real component.

This is just a 2:1 voltage divider between the new value at the driver

output, ( slew rate assumed infinite ), and the prior state of the line,

assumed to be the opposing level, ie +/-Vswing. So, this is where the

Vswing/2 term comes from.

The power transferred to the resistor is the power formula V^2/R, which

is ((Vswing/2)^2)/Rterm.

This condition persists until the wave propagates to the far-end, where

it reflects 2:1, ( completely open end ), and then propagates back to

the driver. When the return wave reaches the driver, the line is at

equilibrium, and the voltage across Rterm collapses to zero. So, this

yields an energy for a change from one symbol to the other of:

(( Vswing/2 )^2)/Rterm * 2 Tflight.

I actually made a mistake in the original representation, as this

applies to all symbol transitions.

So, power is just the energy per symbol multiplied by the symbol

repetition rate:

(( Vswing/2 ) ^2)/Rterm * 2 Tflight * Symbol_rate = Vswing^2 * Tflight *

Symbol_rate / ( 2 * Rterm ).

The actual power is just a tiny bit more, as loading at the far end

prevents a perfect 2:1 reflection. However, the residual power is

generally negligible.

Regards,

Steve.

Dear Steve,

Could you please suggest how to derive the equation, you show below?

Series R power = ( ( Vswing / 2 ) ^ 2 / Rterm ) * Tflight * Symbol_rate.

( 2 * Tflight cancels Symbol_rate / 2 )

Does somebody have any clues about the derivation of the equation?

Thank you for your comments.

Best Regards,

John Lin

Senior SI Engineer, Server Team, ARD4

Quanta Computer Inc.,Taiwan, R.O.C.

Email: John@quantatw.com

Tel: 886+3+3979000 ext. 5183

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**Next message:**Jay Diepenbrock: "[SI-LIST] : internal timestep too small in transient analysis"**Previous message:**sunil-chandra.kasanyal@st.com: "[SI-LIST] : Centre Tap Termiation"**In reply to:**ªL´Â·×: "RE: [SI-LIST] : Any standards of the derating of Capacitors,Resit ors, and inducto rs?"

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