[SI-LIST] Re: Decoupling for PLL (continued)
- From: zhangkun 29902 <zhang_kun@xxxxxxxxxx>
- To: cgrassosprint1@xxxxxxxxxxxxx
- Date: Sun, 05 Sep 2004 07:24:59 +0800
Chas
I used bead. It resonated below 1MHz for the capacitor is too many.
Best Regards
Zhangkun
2004.9.5
----- Original Message -----
From: Charles Grasso <cgrassosprint1@xxxxxxxxxxxxx>
Date: Sunday, September 5, 2004 6:33 am
Subject: [SI-LIST] Re: Decoupling for PLL (continued)
> Hi Zhangkun,
>
> Its very important to differentiate between an inductor and a
> ferrite bead.
> A ferrite bead typically has minimal impedance in the kHz range
> and really
> only
> starts to kick in in the 10s of MHz range. An inductor, on the
> other hand,
> can
> exhibit LARGE reative impedance in the kHz range (depending on the
> value) -
> but
> will also exhibit resonances that need to be damped.
>
> Chas
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Zhangkun
> Sent: Thursday, September 02, 2004 10:53 PM
> To: si-list
> Subject: [SI-LIST] Decoupling for PLL (continued)
>
>
> Dear all
> Recently, I have done some measurement. It is found that when the
> bead(inductor) is used, the power ground noise at 333KHz from VRM
> is larger.
> There is some noise near the clock frequency points.
>
> For example, the output clock of PLL is 50MHz. At 50.333MHz and
> 49.667MHz,there is noise, which is in proportion to the noise at
> 333KHz. Maybe the PLL
> modulates the noise of VRM into the output clock.
>
> Is there any SPICE model for PLL?
>
> Best Regards
>
> Zhangkun
> 2004.9.3
>
>
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