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.