[SI-LIST] Re: Decoupling for PLL
- From: Zhangkun <zhang_kun@xxxxxxxxxx>
- To: Clifford van Dyk <clifford@xxxxxxxxxxxxx>
- Date: Fri, 27 Aug 2004 17:19:11 +0800
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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