[SI-LIST] Capacitivly Coupled Interfaces
- From: "Moeller, Merrick" <Merrick.Moeller@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 16 May 2005 10:06:56 -0500
I have been reasearching the effect of capacitivly coupled
interfaces on data transmission. There are a number of effects that
contribute to the ability of this type of interface to function at a
specificed
data rate. The high pass nature of this type of interconnect (RC Filter)
gives a frequency response very much like a typical RC filter. Using
this
we can determine what spectral content created by our pattern will
pass. This being in simple terms, comes down to "How much capacitance
is needed for the proper filter response?" Simple enough.
My problem has been in the following. The filter responces that
are set up by this interface also have a contributing RC time constant.
The
period of the data and the run length limit are related to this filter
constant.
For example a run of 5 0's will allow for the capacitive element to
charge
at the rate described by the time constant. This will cause what is know
as "voltage droop". Where in the signal will degrade due to the charging
of
the capacitive element. This "droop" also is responcible for a
measureable
amount of "Pattern Dependant Jitter". Ok after all that is said...
Is the effect of changing time constant accounted for in the
high frequency filter response of the interface, or are the effects to
be
considered as separate contributors to the loss in the interface?
Intuitively
the high pass response doesn't seem like insertion loss, but really can
be thought of as another representation of a loss budget.
Regards,
Merrick M. Moeller
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