The analysis of transient waveform and common mode noise on differential broadside-coupled delay lines

In the past, conventional edge-coupled differential serpentine and spiral delay lines were widely employed to minimize the clock skew and to compensate the time skew between two differential pairs in high speed printed circuit boards application. Now, in order to minimize the circuit size in a miniaturized design, the spacing between two parallel adjacent unit lines of delay line will be closer and closer, but it is facing electromagnetic coupling and crosstalk noise from adjacent lines. Furthermore, the time skew between positive and negative lines of the edge-coupled differential delay lines results from the lines with non-symmetrical right-angle bended routing, the common mode noise will also get higher and higher. Thus, new differential routing schemes of serpentine and spiral delay lines with broadside-coupled geometry were proposed to reduce the common mode noise. Moreover, in order to validate the accuracy of presented inductive and capacitive circuit models applied to broadside-coupled geometry, the 3-D full wave simulation and measurement validations of near-end crosstalk noise, far-end crosstalk noise and eye diagram have been also implemented in this paper. It is shown that the measured results are in good agreements with the simulated results.