An Adaptive Impedance Matching Transmitter for a Wireless Intraoral Tongue-Controlled Assistive Technology

A robust wireless communication is critical for wireless intraoral devices since it is adversely affected by the external radio frequency (RF) interference and impedance variations of the transmitter (Tx) antenna in the dynamic mouth environment. We present a three-band (27 MHz, 433 MHz, and 915 MHz) Tx with an adaptive antenna impedance matching system for a wireless intraoral tongue controlled assistive technology (AT), the intraoral tongue drive system (iTDS), to establish a robust wireless link between the intraoral device and an external receiver (Rx). With a built-in super-regenerative receiver (SR-Rx), the Tx can switch the carrier frequency to avoid RF interference without the users' involvement. The upper two bands, 433 MHz and 915 MHz, are equipped with adaptive matching networks and a matching algorithm to automatically correct impedance variations of the Tx antenna without any assistance from off-chip components. The Tx chip was fabricated in a 0.35-μm CMOS process. Measurement results show the tuning range of the proposed network can cover up to VSWR = 4 with 4.7 dB and 3.8 dB output power improvement at 433 MHz and 915 MHz, respectively.