High speed signal compensation on printed circuit boards

Abstract

Data transfer rates on printed circuit boards are quickly approaching speeds that challenge the limits of today’s technology. Inter-chip communication has increased dramatically. Currently data rates have reached 3.125 Gb/s on standard circuit board, but chip-to-chip digital communication has currently reached a plateau and several problems need to be addressed to significantly increase data transfer rates. Inductive and capacitive components of far end crosstalk (FEXT) conveniently cancel each other as they propagate on an interconnect transmission line, however the inductive and capacitive components of near end crosstalk(NEXT) add together and interfere with signals on adjacent receivers.This paper proposes a novel solution for canceling crosstalk by adding extra circuitry to the receiver within the integrated circuit. This digital circuit delivers one of three appropriate levels of crosstalk compensation to the incoming signal. Since the circuit is digital, simple blocks can be used to implement it on a complimentary metal-oxide semiconductor (CMOS) integrated circuit and consume very little extra silicon.This paper presents the compensation circuit and reports the results of the simulations, which demonstrate improved performance over the standard system. The compensation circuit is specifically aimed at adjacent input and output lines on a microchip. Simulations of a typical circuit board configuration operation have shown crosstalk that is only 15 dB lower than a received attenuated signal. The crosstalk cancellation circuit has been shown to improve this by as much as 10 dB.