Crosstalk (Noise) in Digital Systems.

Crosstalk (Noise) in Digital Systems.

Ivor Catt. 1967

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Crosstalk (Noise) in Digital Systems

Pages 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , some of which is in two of my books. The argument starts at page 30 of one book , and at page 4 of the other book , continuing on page 55 . Here in figure 9.2 we see “a very narrow pulse introduced at the front end of the active line. If there were no parallel passive line nearby, this pulse would travel down the active line (at the speed of light for the dielectric) more or less unchanged,” in a TEM mode. “However, as the other two traces show, the presence of the passive line caused the original narrow pulse to break up into two similar pulses.”

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Published in 1967, this paper of mine announced that crosstalk between parallel conductors involved two velocities. If a asignal is delivered to an (active) conductor in a surface microstrip or buried stripline in the presence of a parallel second (passive) conductor, the original signal breaks up into two signals, the Odd Mode and the Even Mode. In the odd mode, the signal in the two sires is equal and opposite. In the even mode, the signal in the two conductors is equal, See the diagram. However, using the method of images, it is preferable to think in terms of this diagram , where the active line A on the top left has its image B below, and the passive line P on the right has its image Q below. In each mode, it is as though pairs of conductors are shorted together as shown.

In the case of the surface microstrip, more of the Odd Mode signal is in the air, so that the effective dielectric constant is lower. This leads to a higher velocity. However, in the case of buried striplines between two voltage planes, the dielectric is all epoxy glass, and so the velocity of the two modes, odd and even, is the same. In the surface lines, the two modes separate out, but in the buried lines, the two modes stay together. In the buried lnes, the signals are pure TEM. In the case of the surfaace lines, the signals approximate closely to TEM.