[SI-LIST] Re: Stack up for EMI reduction,plane resonance and u-str ipradiation etc etc
- From: "Vishram Pandit" <vishrampandit@xxxxxxxxxxx>
- To: zhang_kun@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Mon, 16 Feb 2004 03:26:44 +0000
Zhangkun,
I have a comment on b, You mention:
>"b)I have done some measurement. No matter have many caps are placed on the
boards, the impedance of PDS beyond 200MHz will not get better. It should be
clarified that now I do not use cap less than 1000pF."
It depends on your stack up. If you have power and ground plane adjacent to
each other, this may be true. But if you have say 6 or 8 layer stack up with
second layer ground and last but one layer power, then you can use lower
value caps to reduce the impedance of the power and ground at higher
frequencies (>200MHz). I have used caps as low as 100pF to reduce the
impedance between P/G. With say 1-2nH via inductance, the effect of the
caps is very local, but several of the caps can be placed strategically at
hot spots. It immensely helps alleviate EMI.
Thanks,
Vishram
>From: Zhangkun >Reply-To: zhang_kun@xxxxxxxxxx >To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Stack up for EMI reduction,plane resonance and u-str
ip radiation etc etc >Date: Fri, 13 Feb 2004 09:42:15 +0800 >>Dear all: >>I
have reviewed the mails in this thread. The following is my points. >>a)From
my view, I am caring about the EMI of PCB. Very small common mode noise will
give rise to critical EMI problem. In my experience, the common mode noise
isproportional to the impedance of power delivery systems. This has been
verified by measurement and simualtion. >>b)I have done some measurement. No
matter have many caps are placed on the boards, the impedance of PDS beyond
200MHz will not get better. It should be clarified that now I do not use cap
less than 1000pF. When the caps less than 1000pF is used, there will be a
lotof antiresonance. This is also verified by simualtion and measurement.
>>c)I have not studied the interaction between signal in trace and noise in
plane. However, I have treated one case, in which the noise in plane
seriously affect the signal in trace. After we eliminate the noise in plane,
the signal become very good. >>Best Regards >>Zhangkun >2004.2.13
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