This transceiver for smart pills is a first breakthrough in imec’s aspiration to realize autonomous ingestible sensors that can measure health parameters such as gut health and transmit in real time the data outside the body.
Digestive processes and gastrointestinal diseases are hard to diagnose. Current procedures like endoscopic inspection and stool sample analysis are uncomfortable and only provide one-time observations. Ingestible health trackers, small enough to be swallowed, could collect information over a longer period of time and transmit the data outside the body. Moreover, fixating the ingestible sensors along the gastrointestinal tract, enables longer recordings in specific places of interest. Also, this would increase the comfort of the patient, as he or she could stay out of the hospital while data are collected and sent in real time to the doctor.
One of the challenges in realizing smart pills (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’s new wireless transceiver 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 40nm CMOS and includes on-chip tunable matching network (TMN) that enables a miniature 400 MHz antenna, and as such avoids external and bulky matching components.
The whole transceiver module including antenna occupies a volume less than 55 mm3 which is up to 30 times smaller than state-of-the-art devices. The whole wireless module occupies an area of 3.5- by 15-mm, including a 3.5- by 3.8-mm PCB and a miniature 400 MHz antenna.
The small form factor is realized thanks to a new crystal-free transceiver architecture, alleviating the need for an off-chip crystal device, and a 2 mm2 transceiver IC with the on-chip TMN. Small area is further achieved by a TX/RX shared matching network with only one on-chip inductor and a single-branch phase tracking RX.
While inside the body the smart pills are covered my 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. It ensures a reliable and interference-free channel for the implants.
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. To realize crystal-free operation, imec implemented an over-the-air network-assisted carrier recovery for large frequency offsets of up to 320 ppm.