[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 23:08:03 -0400
Zhangkun,
10mV should not matter. But just in case, to completely rule
out the possibility of having this problem due to DC drop, you
should also measure the DC voltage with your 0-ohm resistor.
Regards,
Istvan
----- Original Message -----
From: "Zhangkun" <zhang_kun@xxxxxxxxxx>
To: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>; "Clifford van Dyk"
<clifford@xxxxxxxxxxxxx>
Cc: <si-list@xxxxxxxxxxxxx>
Sent: Friday, August 27, 2004 8:51 AM
Subject: [SI-LIST] Re: Decoupling for PLL
> 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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