[SI-LIST] Re: nonlinear in power ground noise of clock driver
From: Ravinder.Ajmani@xxxxxxxx
To: si-list <si-list@xxxxxxxxxxxxx>
Date: Thu, 4 Dec 2003 09:16:27 -0800
A solid Tantalum capacitor has ESR of several hundred milliohms, whereas
ESR of a Ceramic capacitor is about 10 -20 milliohms. Perhaps this is
what makes such a large difference in the noise reduction properties for
the two types of capacitors. Another experiment you can try is to replace
the Tantalum capacitor with a Polymer Tantalum capacitor, which has ESR
below 100 milliohms. If this causes significant reduction in power supply
noise then ESR is the key factor.
Regards, Ravinder
Server PCB and Flex Development
Hitachi Global Storage Technologies
Email: Ravinder.Ajmani@xxxxxxxx
Zhangkun <zhang_kun@xxxxxxxxxx>
Sent by: si-list-bounce@xxxxxxxxxxxxx
12/04/2003 03:50 AM
Please respond to zhang_kun
To: si-list <si-list@xxxxxxxxxxxxx>
cc:
From: si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] nonlinear in power ground noise of clock
driver
Dear All:
Recently, my colleague found out something interesting about clock driver.
In our product, CDC2516 of TI is used as clock driver. The clock frequency
is 100MHz. The power of CDC2516 is isolated by one bead. There is some
local decoupling caps as following:
several 0.1uF or 0.01uF ceramic cap
one 10uF tan cap
We measure the power ground noise of CDC2516. The power ground noise is
about 700mV. The spectrum of the noise is at 100MHz, 200MHz, 300MHz, and
so on.
We use several method to decrease the noise. Theere is no use.
My colleague change the 10uF tancap to one 10uF ceracap(X7R). The noise
decrease to 17mV. I am a little confused. I have simulate the impedance of
decoupling circuit. There is no difference in frequency domain beyond
30MHz between using 10uF tancap and 10uF ceracap. According to my
experience, the power ground noise should not decrease.
I think there is something nonlinear. I am not familar with the circuit of
clock driver. There is no SPICE model of CDC2516 in TI website. Therefore
I could not simulate the power ground noise.
Could you give me some advice?
Best Regards
Zhangkun
2003.12.4
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