[SI-LIST] Re: [Bulk] Re: Decoupling for PLL

Ray

I use bead and caps. The caps is of 10uF(Tan), 0.1uF(cera), and 0.01uF(cera).

Best Regards

Zhangkun
2004.8.28
----- Original Message ----- 
From: "Ray Anderson" <reanderson@xxxxxxxxxxxxx>
To: <zhang_kun@xxxxxxxxxx>
Cc: "steve weir" <weirsp@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Friday, August 27, 2004 10:26 PM
Subject: [SI-LIST] Re: [Bulk] Re: Decoupling for PLL


> Zhangkun-
> 
> Can you tell us what values of L and C you are using in your filter ?
> 
> One other thought that I had, which may or may not bear on this 
> particular problem is this:
> 
> Besides isolating the noise on the PDS from your PLL, the low pass 
> filter also, to some extent, prevents noise generated by the PLL from 
> getting back onto the main PDS planes or busses. A simple L section 
> filter (N=2) operating in the backwards direction (CL versus LC) will 
> exhibit a different impedance on the "L" side than it does on the "C" 
> side. I'm wondering if it is possible that you might be developing some 
> noise at the PLL pin across the impedance of the filter L that you don't 
> develop across the zero ohm resistor? Perhaps your PLL likes seeing a 
> very low Z at it's power pin.....
> 
> Just a thought, perhaps not relevant, but I thought I'd through it out 
> for discussion.
> 
> -Ray
> 
> 
> Zhangkun wrote:
> 
> >steve
> >
> >I have measured the power ground noise by spectrum analyzer. There is no 
> >obvious difference.
> >
> >At some frequency, when the inductor(bead) is changed to resistor, the power 
> >ground noise become larger. I am confusing.
> >
> >Best Regards
> >
> >Zhangkun
> >2004.8.27
> >  
> >
> .
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