Fully Autonomous System-on-Board with Complex Permittivity Sensors and 60 GHz Transmitter for Biomedical Implant Applications

This paper presents a system on board (SoB) solution intended for fully autonomous implantable continuous monitoring of biomaterials. The proposed SoB is built around a packaged highly-integrated chip, which comprises two capacitive resonant-tank-based complex permittivity dielectric sensors operating in K-band, temperature sensor, wakeup timer, finite state machine (FSM), serial peripheral interface (SPI), ADC and a 60 GHz transmitter. Wakeup timer is used to turn on the 1.5 V power domain regularly every 8.9 min, which stays "on" only for 4.2 ms. During this time the FSM implements the fully autonomous functionality of the system by running a pre-defined sequence, performing the sensor measurements and forwarding the data to transmitter. The sensor data is read via SPI, buffered and transmitted outside of the implant as a Manchester coded BPSK sequence modulated onto a 60 GHz carrier. The chip is realized in a 130 nm BiCMOS process and packaged using a flip-chip ball-grid array technology. To save chip area, the 60 GHz antenna is realized in the redistribution layer (RDL) of the package. The SoB additionally comprises an external PLL, low-dropout regulators and external reference oscillator. The size of the SoB module is only 18 mm × 14 mm. It can operate up to 233 days from a small 3.7 V LiPo 95 mAh battery. The functionality is verified in measurement by monitoring the fully autonomous sequence. Next, biological materials are applied to the sensor, modulated values are transmitted and demodulated using an external 60 GHz down-converter and digital Costas loop. Finally, isopropanol-water solutions are applied in 25% concentration change steps and demodulated complex permittivity values are evaluated.