[SI-LIST] Re: nonlinear in power ground noise of clock driver
- From: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>
- To: <zhang_kun@xxxxxxxxxx>, "si-list" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 4 Dec 2003 08:14:27 -0700
Zhangkun,
First, are you sure the second cap was ceramic (X7R)? Seems pretty big for
a ceramic. Second, the only thing I can think of is the difference in
mounted inductance.
Ken
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Zhangkun
Sent: Thursday, December 04, 2003 4:50 AM
To: si-list
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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