TECHNICAL FIELD

Embodiments described herein generally relate to electronics and wireless communications and, more particularly, to high-quality-factor (high-Q) resonant circuitry for driving and reading communications devices.

BACKGROUND

A radio-frequency identification (RFID) reader generates electromagnetic fields to energize and interrogate a RFID tag or other compatible communications device located within communication range of the reader. The RFID tag may use the energy supplied by the reader's driving signal, or another source of power, to communicate information to the reader using RF signaling. RFID has found applications in a wide variety of areas, including asset tracking, security, supply chain logistics, manufacturing, testing and measurement, and myriad others.

In one type of application, biocompatible RFID tags have been proposed for use with implantable medical devices for transcutaneous communication. These types of applications present several notable challenges to system designers. For one, the body tends to absorb and attenuate RF signals, particularly high-frequency RF signals, which are able to carry higher bandwidths. In addition, the transmit power of RFID readers for use in implantable-tag applications is often limited for safety reasons. Since an implanted tag is not visible in the absence of imaging instruments, achieving an optimal positioning and alignment between the reader and the tag can be particularly difficult. Moreover, some patients, such as children or animals, tend to have difficulty keeping still during reading of the tag. These challenges compound to make RFID-based implantable sensors difficult to implement in practice.

Related challenges may be found in other applications. For example, underwater environments, longer-range reading, and RFID reading in RF-noisy environments, each exacerbate the difficulty of reliably reading RFID tags.

High quality-factor (Q) radio circuitry has been proposed for use in RFID systems. High-Q radio communications use a specially-designed antenna and radio front end circuitry to emit a particularly strong RF field for a given transmit power, in a narrow frequency band, using principles of electromagnetic resonance. High-Q RFID readers and tags can improve communications performance in environments where distance, signal attenuation, or interference may pose challenges. However, high-Q systems also introduce particular challenges of their own. For instance, a high-Q transmitter in a RFID reader may overload the tag. In addition, a high-Q system tends to be very sensitive to frequency deviations and instability. Also, high-Q RF communication systems tend to suffer from group delay, where different frequencies experience different amounts of time delay in the receiver.

Solutions are needed to address these, and other, challenges in RFID reading applications.

