[SI-LIST] Re: target impedance profile

Zhengang,

We took v(t) = Inverse FFT (Z(f) x I(f)) to look at the time domain noise.
Remember to have both the real and imaginary (or magnitude and phase)
portions of Z(f) and I(f) so the coherency of the noise components add or
subtract properly when the Inverse FFT is performed.

Steve

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of ZHENGGANG CHENG
Sent: Saturday, May 24, 2008 5:27 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] target impedance profile

Hi all,
It seems many SI engineers are using the method described below to define
the target impedance profile for PSD:


Z(f) = 0.05*V_DC/I(f)                    or Z_target=0.05*V_DC/Imax(f)

Z(f)---target impedance profile at freq f;

Z_target---target impedanace at all freq;

0.05---allowed tolerance;

V_DC---power raill;

I(f) ---current profile;

Imax(f)---max I(f)---generallt 0.5Imax(t).

But this setup does not guarantee the overall noise is 5%.  All it does is
making sure noise at each of the frequency of interest is less than 5%.  In
time domain, the combined content has the possibility of bigger than 5%.

So is there a better way to define target impedance profile?

Thanks,

Zhenggang Cheng


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