A Low-Power Wireless Transmitter for a Continuous Glucose Monitoring System-on-Chip

Abstract

Continuous glucose monitoring (CGM) can improve diabetes management by providing frequent measurements and revealing trends that are difficult to capture with invasive, intermittent tests. To this end, a miniaturized, wearable sensing platform that operates continuously and delivers timely alerts is beneficial for individuals who require active glucose management.

This thesis presents a wireless transmitter, implemented in a complementary metal-oxide-semiconductor (CMOS) integrated circuit technology, for energy-efficient telemetry of biomedical signals from a wearable device that transmits short packets to a smartphone, enabling practical daily readout. Since the transmitter must meet Bluetooth Low Energy (BLE) constraints under a tight energy budget, several circuit and system-level design choices that balance frequency accuracy, spectral compliance, and robustness to process-voltage-temperature (PVT) variation at low supply voltages must be made.

The proposed wireless transmitter is one component of a larger mixed-signal system-on-chip (SoC), which integrates a commercially-available electrochemical sensor that interacts with glucose and/or ketones, to enable continuous concentration measurement. The sensing front-end electronics of the SoC converts chemical activity into an electrical signal that is conditioned and digitized on-chip. This measured concentration is then encoded for BLE-compatible transmission by modulating the digitized data using Gaussian frequency-shift keying (GFSK) in the 2.4 GHz industrial, scientific, and medical (ISM) band, implemented as an integer-N charge-pump phase-locked loop (CP-PLL) with direct voltage-controlled oscillator (VCO) modulation.

Simulated and experimental results from a fabricated prototype chip demonstrate the feasibility of the proposed approach in terms of sensor readout, burst energy, and BLE spectral compliance. Implemented in a 0.18 µm bulk CMOS process, the fabricated transmitter delivers -7.06 dBm at 13.5 mW DC power, with an intra-packet drift of 41.56 kHz and reference spurs of −26.4 dBm at ±2 MHz offsets — both within BLE LE 1M limits. End-to-end validation confirms the successful reception of BLE advertising packets on a commodity Nordic nRF5340 receiver, with the digitized electrochemical sensor data reconstructed from over-the-air stream. The presented methodology provides a foundation for compact wearable bio-sensing platforms, combining continuous chemical sensing with standardized wireless communication for patient-facing monitoring and alerts.