[SI-LIST] Re: SSN Vs Load cap
- From: Canes Venatici <starsilic@xxxxxxxxx>
- To: Ihsan Erdin <erdinih@xxxxxxxxx>
- Date: Tue, 6 Feb 2007 03:06:50 -0800 (PST)
sso noise = L.di/dt = LCd2v/dt2 implies, for a constant L and once we'd reached
the
peak driving current, the increase in cap, reduces the dv/dt. So noise should
be constant.
But, since noise is prop. to d2v/dt2, the increase in cap makes, d2v/dt2 term
to reduce much more than dv/dt.
So the SSO noise reduces.
This is simple as i and v are dual to each other.
Correct me if I'm wrong.
----- Original Message ----
From: Ihsan Erdin <erdinih@xxxxxxxxx>
To: starsilic@xxxxxxxxx
Cc: sabbu1981@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Sent: Friday, February 2, 2007 6:33:17 PM
Subject: Re: [SI-LIST] Re: SSN Vs Load cap
Canes,
Sabayachi's explanation is plain and accurate. i=Cdv/dt is a lumped
approximation to Maxwell-ampere eq.; so is v=Ldi/dt to
Maxwell-Faraday. As such, both have physical connotations. Your
di/dt=Cdv2/dt2 is mathematically correct but doesn't have any useful
physical connotations.
Regards
Ihsan
On 2/2/07, Canes Venatici <starsilic@xxxxxxxxx> wrote:
> Upto the maximum current driving capability of driver, the increase in load
> capacitance causes
> the current rate to increase and noise increases, so SSO index should reduce.
> Once its reached the maximum drive capability at a particular load cap, the
> increase of cap
> causes the rate of voltage to fall, as per the max. current spec. But since
> the current remains same (as the driver
> cant supply more than that), I expect SSO index to be unchanged.
> Equations :
> i = c. dv/dt
> di/dt = c.(d2v/dt2) ....(its d square v by dt square)
> sso noise = L.di/dt = L.c.(d2v/dt2).
>
> Please clarify, if I'm missing anything.
>
> Regards
> Canes
>
> ----- Original Message ----
> From: Sabyasachi Mohapatra <sabbu1981@xxxxxxxxxxx>
> To: si-list@xxxxxxxxxxxxx
> Sent: Thursday, February 1, 2007 6:13:12 PM
> Subject: [SI-LIST] Re: SSN Vs Load cap
>
> It is pretty simple.
> as u increase the load cap with same drive strength of driver,
> rise or fall slew will degrade.
> As the buffers will be switching slower now, dI/dt will be less,
> rate of change of current though package inductor will be less.
> So less SSO noise.
>
> --- In si-list@xxxxxxxxxxxxxxx, Canes Venatici <starsilic@...> wrote:
> >
> > Hi all,
> > I couldn't understand why if load capacitance is increased, SSN is
> reduced (as the recommendation is increased SSO index, more signal
> pads can be accommodated by power pads).
> > As di/dt is directly proportional to load cap, increasing the load
> causes more drop in parasitic inductance and SSN should increase.
> > Could anyone clarify.
> > Thanks,
> > Canes
> >
> >
> >
> >
> >
> >
> >
> >
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