[SI-LIST] Re: Bandwidth & AC coupling capacitor
- From: Richard Jungert <r_jungert@xxxxxxxxxxx>
- To: steve weir <weirsi@xxxxxxxxxx>, si list freelist <si-list@xxxxxxxxxxxxx>, <icermail@xxxxxxxxx>
- Date: Sun, 31 May 2009 14:33:39 -0700
Steve
The inductance your talking about it way above the SRF. Is this inductance
value going to work each time for any capacitor ( with the same value ) that is
stuffed in there? What if we change capacitor manufacturers and the process
for making them is slightly different and so the inductance your talking about
is different? This kind of problem one also needs to also consider if your
going to manufacture the product. Maybe in this case one would need to pick
one manufacturer/process for this specific part function.
Richard Jungert
> Date: Sun, 31 May 2009 13:23:24 -0700
> From: weirsi@xxxxxxxxxx
> To: r_jungert@xxxxxxxxxxx
> Subject: Re: [SI-LIST] Re: Bandwidth & AC coupling capacitor
>
> Richard from a circuit standpoint it is somewhat simpler than a typical
> line equalization problem such as long video transmission lines. So
> long as the capacitor is selected such that the mounted SRF is well
> below any signal frequencies, the dominant reactance is entirely
> inductive. This is readily compensated with a pure capacitance which is
> readily manipulated through the pad and ground clear out patterns. The
> compensation works provided that the structure is small compared to the
> shortest wavelength of interest.
>
> Best Regards,
>
>
> Steve.
> Richard Jungert wrote:
> > I would suggest finding out where the losses are or where the first
> > pole occurs and then building a LC compensation network to address the
> > problem with rolloff. Peak it where the rolloff occurs. Use
> > compensation and equalization circuits to fix it.
> >
> > This is how it has been done in other technologies such as analog
> > video for years.
> > Its an age old problem.
> >
> > Richard Jungert
> >
> > > Date: Sun, 31 May 2009 03:34:29 -0700
> > > From: weirsi@xxxxxxxxxx
> > > To: icermail@xxxxxxxxx
> > > CC: si-list@xxxxxxxxxxxxx
> > > Subject: [SI-LIST] Re: Bandwidth & AC coupling capacitor
> > >
> > > It is all about the series impedance and impedance continuity. Your PCB
> > > etch is nominally a 50 Ohm signal transmission line. From about an
> > > octave above the mounted SRF, the capacitor looks like an inductor with
> > > some loss. If the interconnect in the region of the capacitor is
> > > arranged such that the parasitic shunt capacitance Cshunt =
> > Lcap_mounted
> > > / 2500, then for wavelengths that are long compared to the length of
> > the
> > > region surrounding the capacitor, the L/C approximates the impedance of
> > > the rest of the transmission line and there is little impedance
> > > discontinuity.
> > >
> > > Steve.
> > >
> > >
> > > icer world wrote:
> > > > When use AC coupling for interconnection,the capacitor is about
> > 0.1-0.01uF.However,the resonance frequency of this kind capacitor is
> > below 100MHz,Would signals above 1GHz such as PCIe signals can pass it
> > without no bandwidth reduced?Can anyone give me a explanation? Thanks!
> > > >
> > > >
> > > >
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> --
> Steve Weir
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
>
> California office
> (866) 675-4630 Business
> (707) 780-1951 Fax
>
> Main office
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> Oregon office
> (503) 430-1065 Business
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>
> http://www.teraspeed.com
> This e-mail contains proprietary and confidential intellectual property of
> Teraspeed Consulting Group LLC
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