Reduction of crosstalk noise in modular jack for high-speed differential signal interconnection

Abstract

Crosstalk noise has become a significant problem in the design of high-speed digital interconnections. In this paper, we demonstrate a crosstalk reduction method, which has been successfully applied to the design of a CAT-5E modular jack. The CAT-5E is a newly adopted cabling and connector standard for advanced cabling network systems to assure more robust, reliable and high-speed operation, which is based on differential mode signal transmission using unshielded twist pair (UTP) cable. The improved design of the modular jack shows minimal crosstalk noise and return loss over a wide range of manufacturing conditions. The improved crosstalk characteristics of the modular jack were accomplished by inserting embedded capacitors on the printed circuit board (PCB) of the modular jack. The embedded capacitors compensate for the unbalanced capacitive crosstalk that occurs in the plug and insert. In particular, the embedded balancing capacitor is designed to have maximum capacitance, with limited PCB area, by using a double-sided PCB design. Less than -45 dB near-end-crosstalk (NEXT) was achieved after the crosstalk noise compensation, satisfying the CAT-5E specification for frequencies up to 100 MHz.