[SI-LIST] Re: Decoupling for PLL
- From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: <zhang_kun@xxxxxxxxxx>, "Clifford van Dyk" <clifford@xxxxxxxxxxxxx>
- Date: Fri, 27 Aug 2004 08:53:30 -0400
Zhangkun,
What do you mean by "there is no problem"?
Even if the DC voltage is within spec, the differing
DC voltage with 0-ohm resistor and with inductor
may contribute to the mystery. A control experiment
in this case would take a resistor with a value that
produces the same DC voltage you get with the
inductor, and see what happens in that case.
Best regards,
Istvan
----- Original Message -----
From: "Zhangkun" <zhang_kun@xxxxxxxxxx>
To: "Clifford van Dyk" <clifford@xxxxxxxxxxxxx>
Cc: <si-list@xxxxxxxxxxxxx>
Sent: Friday, August 27, 2004 5:19 AM
Subject: [SI-LIST] Re: Decoupling for PLL
> Clifford
>
> I have measure the DC voltage. There is no problem.
>
> Best Regards
>
> Zhangkun
> 2004.8.27
> ----- Original Message -----
> From: "Clifford van Dyk" <clifford@xxxxxxxxxxxxx>
> To: <zhang_kun@xxxxxxxxxx>
> Cc: <si-list@xxxxxxxxxxxxx>
> Sent: Friday, August 27, 2004 2:27 PM
> Subject: Re: [SI-LIST] Decoupling for PLL
>
>
> > Hello Zhangkun
> >
> > You may want to verify that the DC voltage level at you supply pin to
> > your PLL is within spec. Often inductors have a reasonably large DC
> > resistance (even in the order of ohms), that causes significant voltage
> > drop if your PLL draws significant current from the supply. This would
> > explain why your resistor (0R) works fine.
> >
> > Kind regards,
> > Clifford
> >
> > zhangkun 29902 wrote:
> >
> > >Dear all
> > >
> > >I have a question about decoupling for PLL. In one of our PCB, there
are three PLL. PI decoupling circuit is used. When the inductor is used, the
PCB does not work. When resistor of 0 ohm is used, the PCB work well.
> > >
> > >I have measured the power ground noise. The power ground noise in the
two situation is different of 3db, which could be ignored. The power ground
noise is very small. The power ground is about -50dbm at the harmonic
frequency of PLL.
> > >
> > >It is obvious that the key element is the decoupling circuit. However,
when I measure power ground noise, I could not find the obvious difference.
Please give me some advice. Is there anything which could not be measured at
PCB level?
> > >
> > >Best Regards
> > >
> > >Zhangkun
> > >2004.8.27
> > >
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