One challenge with implementing electronic pills is developing a wireless link that meets the volume, power and performance constraints for reliable data transmission during the period of time that the sensor is collecting data inside the body. Imec has developed a wireless transceiver that supports the medical 400 MHz frequency bands such as MICS (Medical Implant Communication Service), MEDS (Medical Data Service) or MedRadio (Medical Device Radiocommunications Service).
The wireless transceiver is implemented in 40-nm CMOS and includes on-chip tunable matching network (TMN) that enables a miniature 400-MHz antenna. The transceiver module occupies a volume of 55 mm3, which is reportedly up to 30 times smaller than state-of-the-art devices. The wireless module occupies an area of 3.5 x 15 mm, including a 3.5 x 3.8 mm PCB and a miniature 400-MHz antenna. The small form factor is achieved using a crystal-free transceiver architecture, alleviating the need for an off-chip crystal device, and a 2 mm2 transceiver IC with the on-chip tunable matching network.
While inside the body, the pills are covered by multiple layers of tissue. Therefore, a wireless system operating in the 400 MHz medical bands is preferable because of lower tissue attenuation compared to higher-frequency bands, which ensures a reliable and interference-free channel for the implants. Furthermore, the on-chip tunable matching network using self-calibration expands impedance matching up to a VSWR (voltage standing wave ratio) of 4.8, covering a wide range of impedance variation in the body, equivalent to a filled and empty stomach.