[SI-LIST] Decoupling for PLL
- From: zhangkun 29902 <zhang_kun@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 27 Aug 2004 00:04:00 +0800
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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