[SI-LIST] Re: Flight Time Approximation
- From: "Ingraham, Andrew" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 12 May 2003 12:38:36 -0400
Adeel Malik,
> Consider the figure shown below or if you can't see that in your Email
> software, view the word attached file
No attachments on this list, they get removed automatically. The figure
didn't come through either.
> I want to find the max. time take by the signal to go from Low to high at
> the receiver input. This time is dependent upon the rise time of the RC
> network formed by the O/P Resistance of Driver and Input Capacitance of
> Receiver plus the propagation delay of the transmission line (whether it's
> microstrip or stripline ...).
If the transmission line is long, the receiver's input capacitance doesn't
"see" the Rout of the driver; it sees Zo, the line's characteristic
impedance. The time constant, which may be R*C for very short lines,
becomes Zo*C for a long line.
For the long line case, the driver's output resistance affects the amplitude
of the first step (and reflections). This can affect the time the waveform
crosses receiver input thresholds too.
> Now my question is that in order to find the complete flight time from the
> driver to the receiver, should we add t1 ( the propagation delay of line)
> to
> t2 (the charging time) or how we should add the delay effect of
> Transmission
> line to the charging time ?>
For a long line (Td >> Trise), it may be a good approximation to add Td and
a factor proportional to Zo*C.
But only as a rough approximation.
Regards,
Andy
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