Abstract
As silicon chip performance continues to increase, the interconnection capabilities should also be improved to achieve higher overall system performance. This paper proposes a new, small-size and high-speed non-contact interconnect between printed circuit boards (PCBs) using a vertical directional coupler (VDC), which has actually been applied to a liquid crystal display (LCD) driver board. The feasibility of a millimeter-range non-contact interface using a directional coupler was studied previously [1]. In this paper, two signal ports have been implemented in one coupler by best utilizing the characteristics of VDC. The coupler size is 5mm × 2.25mm, and the gap between the couplers is about 75μm, which corresponds to the twofold thickness of a soldering resist on PCB and the adhesive material in between. The transmitter transforms the data sequence from Non-Return-to-Zero (NRZ) into pulses in order to reduce the level of DC components. This achieves a power saving of 1.47pJ/b, and the pulses are sent to the coupler in differential mode to prevent electromagnetic interference (EMI). The measured speed was 4.6Gb/s per coupler to achieve the MIPI's maximum speed of 6Gb/s with two couplers. Conventional connectors have housings to protect contact elements or to provide mechanical support for plug-in and out. However, these housings make it difficult to achieve the smallest possible systems because they require extra space. In addition, they sometimes make the PCB trace longer, which deteriorates the maximum data rate. The method we have developed involves delineating VDC on PCB or a flexible printed circuit (FPC) to connect boards without housings and with the minimum distance. As a result, this interconnect scheme is advantageous not only because it saves space but also because it makes it easier to build systems, even those that contain a large number of built-in connectors. Thus, the proposed non-contact interconnect is suitable for future small-size systems.
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