Using Stepped-Impedance Lines for Common-Mode Noise Reduction on Bended Coupled Transmission Lines

Right-angle bended coupled lines with a periodic stepped-impedance line (SIL) structure are proposed to suppress both common-mode noise and differential-to-common mode conversion in this paper. The advantage of the periodic SIL structure shows that it is not only with lower manufacture cost and easier implemented in two-layer Printed Circuit Board (PCB) but also maintains acceptable transmission level and low reflection. The function of the SIL structure is to increase the length of the shorter one of the bended line, i.e., to increase its respective propagation time, thereby improving the signal integrity without largely increasing the circuit size of PCB. Measured result of common-mode noise introduced by right-angle bended coupled lines with SILs structure can be reduced by 83 mV, time skew can be reduced by 31.53 ps, mode conversion can be suppressed from dc to 10 GHz for getting wideband suppression based on -25 dB definition, and measured result of eye-diagram, the eye-opening is improved by 9.97%, all measured results are compared with conventional right-angle bended coupled lines.