A technique for high‐speed digital data transfer based on crosstalk

A high-speed bus is proposed for digital data transfer in which signals enter and exit the main bus via crosstalk between transmission lines. We refer to this type of signal transfer as “crosstalk transfer logic,” or XTL. In XTL, because signals are conveyed by crosstalk coupling in transmission lines with distributed constants circuit (a directional coupler), the noise reflected at the stub line of the main bus is small, making XTL suitable for use at high speeds. Binary nonreturn-to-zero (NRZ) data excited by the driver is differentiated by the directional coupler, which converts it to a polar signal. A hysteresis receiver then demodulates to original signal from the RZ signal. Because the directional coupler and the receiver are the keys to XTL technology, we have evaluated the performance of two kinds of directional coupler, one based on within-board circuit lines and one consisting of ceramic elements. On a printed-circuit board (PCB) capable of holding 8 or 16 modules, we found that the characteristic impedances of the within-board couplers could be kept within a range of ±10% whether the modules were mounted or not, making it possible to transfer signals at 600 Mbit/s. For the ceramic directional couplers we designed 4-bit elements with 5.4×4 mm outline having a performance equivalent to within-board directional couplers with 40 mm of coupler length. This makes data transmission possible at 1 Gbit/s. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(12): 43–52, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20153