A 6nW inductive-coupling wake-up transceiver for reducing standby power of non-contact memory card by 500×

Abstract

Memory cards are widely used in electronic systems to expand internal storage area or are used as detachable media to carry data. Although cloud computing has recently drawn attention, data transfer consumes significant power (e.g., 1% battery charge of a smartphone when 10 pictures are transferred through WLAN), making local memory card storage still attractive in mobile devices. As storage capacity increases, the I/O speed should also increase accordingly. However, conventional memory cards require strong ESD protection, limiting high-speed data transfer. A non-contact memory card [1] is one of the solutions to this problem. No signal terminals are exposed for mechanical contact, which relaxes ESD constraints. A data transfer rate of 6Gb/s/ch by inductive coupling [1] and 12Gb/s/ch by transmission-line coupling [2] are reported. The post-UHS-II speed over 5Gb/s can be covered with around 10mW power consumption. Moreover, by supplying power wirelessly, mechanical connections can be completely removed, which could provide features such as waterproof capability or a new attach-remove user interface. A >50% high-efficient wireless power delivery has been reported [3]. However, it mainly supplies a large amount of active power, and the efficiency drops to ~10% in low-power standby mode. Shutting down the power delivery in standby would require a power-on sequence and an unacceptably long suspend (~10s) for each new command. For high-speed card access, the power delivery and the wireless data receiver (RX) should always be active, consuming about 2mW in RX and in total 20mW including loss in the wireless power delivery. This standby power is almost identical to that of typical smartphones, tablet-PCs, or camcorders and the battery life halves.