30.8 A 3.5mm×3.8mm Crystal-Less MICS Transceiver Featuring Coverages of ±160ppm Carrier Frequency Offset and 4.8-VSWR Antenna Impedance for Insertable Smart Pills

Gastroscopy is a common diagnosis method for gastrointestinal (GI) diseases, but it needs to be performed in hospitals. Existing ingestible pills can collect patients' GI information over a longer period outside of a hospital, and various sensors can be incorporated to collect more information. However, ingestible pills passing through the GI system cannot make long recordings in specific places of interest. New gastroscope research focuses on the use of the biopsy channel of an insertion tube to attach the pill on a specific surface of the GI tract for some time before it detaches itself [1]. One of the most challenging parts of such “insertable” pill design is the volume constraint. The biopsy channels in gastroscopes have a diameter of ~3.5mm (at least 3x less than existing pills), and the length of the non-bendable part should be <; 15mm (Fig 30.8.1). Since the pill is at places covered by up to 15cm of tissue, a wireless system operating in the 402-to-405MHz MICS band is preferable because of lower tissue attenuation compared to higher frequency bands, e.g., 2.4GHz. It also provides a longer communication distance and wider signal bandwidth compared to near-field communication systems [2]. Finally, the interference control in MICS ensures the implants having an interference-free channel. However, the volume constraint poses significant challenge for a MICS transceiver design because external components should be avoided, and it interfaces with an electrically small ( (10) antenna which has high sensitivity to the surrounding environment. A crystal-less transceiver is preferred because the crystal is typically the biggest off-chip component. A mm-scale radio in [3] replaces the crystal with an FBAR but requires a special manufacturing process. A mm-scale crystal-free radio in [4] presented a network-assisted timing synchronization for its Pulse-Position-Modulation(PPM)-based system. However, transceivers operating in MICS must adhere to a carrier stability better than ± 100ppm which mandates carrier synchronization for crystal-free operation, and it is especially critical for FSK/PSK transceivers that are preferred in MICS for their better channel selectivity and interference resilience. Power-oscillator topologies [5] have been widely adopted in recent mm-scale radios owing to their small size and high efficiency. However, the external coil impedance variation due to the direct contact of tissues can influence the carrier stability of the power oscillator, and the power oscillator cannot be reconfigured as an LO for FSKIPSK-based RXs.