Abstract: The present disclosure describes systems and techniques relating to wireless charging of mobile devices, such as smartphones and wearable devices. According to an aspect of the described systems and techniques, a mobile data processing device includes: a display; a processor; a memory system; wireless communication hardware; a battery; a coil; and wireless charging circuitry coupled between the coil and the battery; wherein the wireless charging circuitry is configured to charge the battery using power received wirelessly through the coil, and wherein the wireless charging circuitry is further configured to draw power from the battery and operate the coil to wirelessly transmit the power from the battery to another mobile data processing device.

Abstract: Systems, methods, and other embodiments associated with radio frequency identification (RFID) circuits are described. According to one embodiment, a radio frequency identification circuit includes an antenna network and an integrated circuit configured to operate as a reader and a tag in combination with the antenna network. The integrated circuit is configured to provide an output admittance determined by a ratio of current and voltage negative feedback signals such that a frequency response of the combined integrated circuit and antenna network is adjustable when operating as a reader.

Abstract: Systems, methods, and other embodiments associated with radio frequency identification (RFID) circuits are described. According to one embodiment, a radio frequency identification circuit includes an antenna network and an integrated circuit configured to operate as a reader and a tag in combination with the antenna network. The integrated circuit is configured to provide an output admittance determined by a ratio of current and voltage negative feedback signals such that a frequency response of the combined integrated circuit and antenna network is adjustable when operating as a reader.

Abstract: Systems, methods, and other embodiments associated with radio frequency identification (RFID) circuits are described. According to one embodiment, a radio frequency identification circuit includes an antenna network, including an antenna and an antenna interface coupled to the antenna, wherein the antenna interface includes first and second capacitors, which are coupled in series with the antenna. An integrated circuit includes a first pin and a second pin coupled respectively to a first node and a second node of the second capacitor and configured to operate as a reader and a tag in combination with the antenna network, and an amplifier embedded in the integrated circuit and configured to provide an output admittance determined by a ratio of current and voltage negative feedback signals such that a frequency response of the combined integrated circuit and antenna network is adjustable without increasing power consumption of the RFID when operating as a reader.