[SI-LIST] Re: basic question regarding inductor before Vcc

Steve,
 Can you pls point to a suitable literature (in pdf files or 
url links) to understand the calculations and how to reach 
at appropriate values of 'L' and 'C' elements in bypassing 
network?

Thanks and Regards,
Vijay.C

---- Original message ----
>Date: Fri, 17 Jun 2005 11:37:33 -0700
>From: steve weir <weirsi@xxxxxxxxxx>  
>Subject: [SI-LIST] Re: basic question regarding inductor 
before Vcc  
>To: roymesi@xxxxxxxxx, <si-list@xxxxxxxxxxxxx>
>
>Roy, sure a series impedance decouples the IC from the 
surrounding 
>interconnect.  Done properly, that can be a good thing for 
issues such as 
>EMI.  When a thirsty IC inhales lots of current that wave 
propagates trough 
>the interconnect until it either dissipates due to 
resistive, and radiated 
>losses, or encounters an impedance discontinuity such as a 
decoupling 
>inductor.  That works two ways and can isolate digital 
return currents from 
>traversing a sensitive analog path in an IC such as are 
used for PLLs.
>
>The bad news is that many people design bypass / decoupling 
networks by 
>rote rules and happenstance.  An inductor that isolates an 
IC that is not 
>matched with enough capacitance to supply the IC is a bad 
>thing.  Similarly, a combined inductor and capacitor 
network can peak badly 
>making power quality much worse than without the inductor 
in the first place.
>
>Steve.
>At 07:59 PM 6/17/2005 +0200, Roy M. wrote:
>>Hi,
>>can someone explain to me why the board designers put 
inductors just 
>>before the Vcc connection? is it some kind of filter 
against noises?
>>I understand that when you put a resistor, it is intended 
for lowering the 
>>voltage or for pull-downs... but what's the logical 
explanation for 
>>putting an inductor?
>>Thanks,
>>Roy
>>
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