[SI-LIST] Re: target impedance profile
- From: "tao xu" <helen.tao.xu@xxxxxxxxx>
- To: deltaboy <imsong@xxxxxxxxxxxx>, "ZHENGGANG CHENG" <zhenggang.cheng@xxxxxxxxx>
- Date: Mon, 26 May 2008 09:37:44 +0800
Hi, Zhenggang,
my understanding for the formula is
Z_target = 0.05*V_DC/Iccmax
Z_target---target impedanace at all freq;
0.05---allowed tolerance;
V_DC---power raill;
Iccmax---max I in time domain
A worst case current which changes from 0 to Iccmax suddenly was assumed to
get this formula.
the Z(f) above can gurantee the noise level in time domain is less than 5%.
But the problem is that it is always too ideal to realize in real design.
v(t) = Inverse FFT (Z(f) x I(f)) is a improved method. But is also need to
be employed very carefully since the inverse FFT itself may introduce new
issue.
I am looking forward to get more new idea also from mail thread.
thanks and regards
helen
On Mon, May 26, 2008 at 7:47 AM, deltaboy <imsong@xxxxxxxxxxxx> wrote:
> =C7=C1=B8=AE=C3=A7=B8=DE=C0=CF
> =09 =09
>
> In my case,
>
>
>
> If any system has 16 bit data= , I do simulation for current profile.
>
> For worst case, I make spice = circuit all 16 bit driver and receiver and
> do
> simulation such SSN
>
> , = then measure the current profile via time domain.
>
> V(t)*ripple tolera= nce =3D Z(target) I(profile)
>
> I set the "output variable" lice Z(targ= et) =3D V(t) * ripple
> tolerance/I(profile)
>
> Someone use the stimulus = as random source.
>
>
>
> Good luck.
>
>
> ---------- =BF=F8=BA=BB =C6=ED=C1=F6 ----------
> =BA=B8=B3=BD=BB=E7= =B6=F7: Steve Waldstein
> =BA=B8=B3=BD=B3=AF=C2=A5: 2008/5/24 1= 9:47:59
> =B9=DE=C0=BA=BB=E7=B6=F7: "'ZHENGGANG CHENG'";si-list@xxxxxxxxxxxxx
> =C1=A6=B8=F1: [SI-LIST] Re:= target impedance profile
>
> Zhengang,We took v(t) =3D = 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 orsubtract properly when t= he Inverse FFT is
> performed.Steve-----Original Message-----From: si-list-bo=
> unce@xxxxxxxxxxxxx[mailto:si-list-bounce@xxxxxxxxxxxxx] OnBehalf Of
> ZHENGG=
> ANG CHENGSent: Saturday, May 24, 2008 5:27 PMTo: si-list@xxxxxxxxxxxxxxxxxx
> =
> ct: [SI-LIST] target impedance profileHi all,It seems many SI engineers
> are=
> using the method described below to definethe target impedance profile for=
> PSD:Z(f) =3D 0.05*V_DC/I(f) or Z_target=3D0.05*V_DC/Ima= x(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 pro=
> file;Imax(f)---max I(f)---generallt 0.5Imax(t).But this setup does not
> guar=
> antee the overall noise is 5%. All it does ismaking sure noise at each of =
> the frequency of interest is less than 5%. Intime domain, the combined con=
> tent has the possibility of bigger than 5%.So is there a better way to
> defi=
> ne target impedance profile?Thanks,Zhenggang
> Cheng-------------------------=
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