[SI-LIST] Re: Amplitude loss ?

  • From: "Lynne D. Green" <lgreen22@xxxxxxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Fri, 06 Jan 2012 12:12:23 -0800

As Steve said, follow the energy (power).  
Pout=Vout*Vout/Rload, so smaller P => smaller V.

So - The short answer is energy loss ALWAYS 
reduces both voltage and current at the load 
compared to the output voltage (the two exceptions 
are no reduced voltage for Zout=short, and no 
reduced current for Zout=open).

* Your analysis with an ideal voltage source would 
be improved by adding a non-ideal connection 
between the voltage source and the load, to model 
transmission line loss.

* For a DC representation of interconnect loss, 
try a series-shunt-series- (TEE section) using 3 
resistors of 1 ohm each.  To get a feel for the 
effect of dielectric loss (represented by shunt 
resistor), do the basic circuit analysis with the 
shunt resistor at 1 ohm and then at 100-ohm 
(larger resistance = smaller dielectric loss).  
Even without a load, the voltage is reduced at the 
output.  To get a feeling for trends in output 
voltages, one could repeat the analysis with 
Zout=50 and Zout=100 and check the output voltages 
and currents.

Hope this helps to clarify effects of lossy 
interconnects.

Lynne


PS: before anyone nags me, my circuit example 
values were selected to make it easier to see 
trends.  They are not intended to represent any 
actual T-line.



"IBIS training when you need it, where you need it."

Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@xxxxxxxxxxxxxx




On 1/6/2012 3:14 AM, rajneesh shukla wrote:
> Thanks Steve but question remains unanswered !!
>
>
> I agree there will be a loss in energy due to dielectric loss but I was
> talking about loss in amplitude of signal (voltage) not loss in total
> energy, Energy loss does not always translates into voltage loss, right ?
> Receiver senses voltage( Potential Energy per unit charge) not total energy.
>
>
>
> As per basic circuit theory, If I have a driver that has zero o/p impedance
> is driving a 50 Ohm load and now if I connect 100 Ohm resistance across
> this load, Though there is energy loss due to 100 ohm resistance but still
> my load will see the same voltage, agree ?
>
>
>
> In transmission line, If series loss i.e. conductor loss is zero then I
> don't find the reason of any voltage drop in transmission line coz
> dielectric loss which is shunt loss can only dissipate total energy but
> can't change amplitude(voltage) of signal.
>
>
>
> Do you find any discrepancy in this analogy ?
>
>
> On Fri, Jan 6, 2012 at 2:40 PM, steve weir<weirsi@xxxxxxxxxx>  wrote:
>
>> Follow the energy.  Achieve enlightenment.  Of the energy that a shunt
>> draws, how much of that energy remains available to the signal?
>>
>> Steve.
>>   On 1/6/2012 12:54 AM, rajneesh shukla wrote:
>>> Experts,
>>> As we know for perfectly matched line insertion loss is due to ohmic&
>>> dielctric losses and due to these losses we see loss in rise/fall time as
>>> well as loss in amplitude of signal.
>>>
>>> My question is what actually affects amplitude loss, is it ohmic loss or
>>> dielectric loss ? My understanding says, it should be ohmic loss as
>>> it comes in series coz dielectric one is shunt loss. If this analogy is
>>> correct then a channel having very low ohmic loss but significant
>>> dielectric loss will have only changes in rise time but minimal amplitude
>>> loss, right ??
>>>
>>> Rajneesh
>>>
>>>
>>>
>>> --
>>> Steve Weir
>>> IPBLOX, LLC
>>> 150 N. Center St. #211
>>> Reno, NV  89501
>>> www.ipblox.com
>>>
>>> (775) 299-4236 Business
>>> (866) 675-4630 Toll-free
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>>>
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