Re: [SI-LIST] : Oscillation in lumped circuits and transmission lines

massimo gaspari ++39 010 6002 534 (massimo.gaspari@marconicomms.com)
Wed, 17 Feb 1999 15:43:54 +0000 (GMT)

Dear Arani, you wrote
>
> those phenomena are two disparate animals. They can be easily confused
> because they both include SQRT(L*C).
>
> Consider a ladder model of lossless transmission line. A resonance
> frequency for each step of the ladder is
>
> w=1/SQRT(L*dx*C*dx)=1/(dx*sqrt(L*C)),
>
> where w is in rad/sec, L and C are inductance and capacitance per unit
> length and dx is the length represented by this step of the ladder.
>(This
> frequency incidentally coincides with the cutoff frequency of the
>low-pass
> filter which this ladder step is. Here I will not go into how one
>should
> choose the number of such ladder steps per unit length depending on the
> desired bandwidth of the tline model. This is a separate issue.)

But may be an interesting issue. Usually if Tpd is the propagatio delay
of the line and Trise/Tfall are the rise time and fall time of the
incoming signal I chose


Number of segment = k * ( Tpd / Trise)

where k may be 4,2*PI or 8.

I this way you have k cells in the rise time.

Do you know some other practical rules for this task?

Regards

Massimo Gaspari

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