[SI-LIST] Re: Decoupling for PLL
- From: Zhangkun <zhang_kun@xxxxxxxxxx>
- To: Istvan NOVAK <istvan.novak@xxxxxxxxxxxxxxxx>, Clifford van Dyk <clifford@xxxxxxxxxxxxx>
- Date: Fri, 27 Aug 2004 20:51:16 +0800
Istvan
I have measured the DC voltage at the power pin of PLL. The result is in the
common range. The power is of 2.5V. My measurement result is about 2.49V.
Therefore I think there is no problem.
Do you mean the PLL is very sensitive to the DC voltage?
Best Regards
Zhangkun
2004.8.27
----- Original Message -----
From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
To: <zhang_kun@xxxxxxxxxx>; "Clifford van Dyk" <clifford@xxxxxxxxxxxxx>
Cc: <si-list@xxxxxxxxxxxxx>
Sent: Friday, August 27, 2004 8:53 PM
Subject: Re: [SI-LIST] Re: Decoupling for PLL
> 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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