Turn-key PCB assembly services in prototype quantities or low-volume to mid-volume production runs

Impulse signal distortion in the transmission line

Today most electronic equipment consists of signal generators and processing units. These units are connected with transmission lines. These lines have a big influence on signal distortions. On these lines depends transmission lines stability. Let’s see how transmission lines affect transmitted signals.

(G- signal generator; Za– output impedance; I- signal receiver Zb– input impedance; L- transmission line length; Z0– Line impedance.

When line is tuned and without losses then input voltage:

Ub(t) = ZbE(t-t)/(Za + Zb)

E(t)- generators signal amplitude; t- signal delay in line.

t =l/v ;

l- line lenght; v- signal speed.

If the line is not tuned up, then there are distortions in line because of reflections inline:

If signal E(t) is step function:

Then signal in line exit in discrete time moments will be:

U(0) = p;

U(t) = p*(1+pb)

U(2t) = p*(1+pb+pa*pb)

U(3t) = p*(1+pb+pa*pb+pa*pb^2);

U(4t) = p*(1+pb+pa*pb+pa*pb^2+pa^2*pb^2);

U(5t) = p*(1+pb+pa*pb+pa*pb^2+pa^2*pb^2+pa^2*pb^3) …


Depending on reflectance coefficients and their signs distortions can differentiate or integrate:

A real model using MathCAD was implemented to see how the signal looks on exit depending on parameters. Below you see used algorithm structure used in modeling:

Part 2:

One of results using trapezoid signal:

In exit we get distorted signal.

Download your MathCAD Transmission Line (13, 12, and 2001i versions ) file to test various parameters and different signal shapes.

Leave a Reply