Optimal sub‐harmonic injection‐locked MICS band transmitter for wireless CW‐fNIRS systems

Abstract

Portable and wireless functional near-infrared spectroscopy is a growing field of research for real-time monitoring of brain functions. The most critical challenges in this field are the use of low-power and calibrated circuits. A novel transmitter architecture is proposed to overcome these barriers. This transmitter is low power, capable of being calibrated against process variation, and has a better phase noise and spurious-free dynamic range (SFDR) at the antenna. Besides that, the transmitter can be calibrated, which is not seen in similar research. In this transmitter, injection locking and frequency calibration lead to having an optimal and low-power circuit. The circuit is capable of transmitting data with BFSK and OOK modulations in the frequency band of the medical implant communication service (MICS). The transmitter is designed and simulated in a typical CMOS 0.18-μm technology with a 1-V power supply. The transmitter's power consumption is around 146 and 123 μW, equal to 5.92 nJ/bit and 246-630 pJ/bit for BFSK and OOK modulations, respectively. The signal's phase noise at the antenna is almost À109 dBc/Hz at 1-MHz frequency offset.