Comparison of Electrical and Optical Interconnect

摘要

In this paper, we present a comparison between electrical and optical interconnect for chip-to-chip signaling in terms of data rate and system power consumption on FR4 circuit boards. The results show that optical interconnection is the only functional technology for a single serial line of 20cm length at a lOGbps data rate. Low power CMOS logic driving parallel unterminated copper interconnect on FR4 substrates should be replaced by terminated transmission lines at 10cm lengths for 10Gbps aggregate throughput and at 20cm for IGbps aggregate throughput. Terminated copper transmission line interconnect on FR4 substrates can achieve 10Gbps per line operation at 20cm, provided no vias are used in the interconnect, or via technology with low reflection loss is developed. With vias, terminated copper transmission line interconnect must be replaced at 20cm for lOGbps per line, however, 4 parallel terminated transmission lines with vias each running at 2.5Gbps can achieve lOGbps aggregate communication over a 20cm length. Thus, serial optics should only be used to replace 4 parallel electrical transmission lines if the power dissipation of the optical driver circuitry is less than 4 times the 2.5Gbps electrical driver power consumption. For electrical interconnect, two interconnection technologies were studied. The first technology uses ideal sources to drive a single serial terminated 50Ω copper transmission line on FR4 both with and without vias. The second technology uses conventioinal CMOS digital interface circuits and parallel unterminated, 50Ωtransmission line interconnect of width 16, 32, and 64bits made from copper on an FR4 substrate. These two technologies represent low power CMOS and the ultimate limit of FR4 copper traces for unequalized digital signaling. For optical interconnect, commercial SiGe optoelectronic laser driver circuit technology and published optical waveguide data were used to determine performance limits. Compliance with the IEEE 802.3ae XAUI interface eye mask was used to determine acceptable data transmission in all cases.