An Ultrasound-Powering Transmitter IC with Standing-Wave Peak Tracking for Real-Time Power Regulation of Brain...

Ultrasound (US) can enable power efficient and miniaturized wireless powering of brain implants on the cortical surface. However, due to the presence of ultrasound standing waves, variations of the powering distance drastically affect the power delivered to the load (PDL), making the link unreliable. This paper presents an ultrasound powering transmitter IC with Standing Wave Peak (SWP) tracking, tuning the ultrasound frequency to ensure operation at the peak of the standing wave. Thus, real time implant power (PDL) regulation under powering distance variations is achieved. First, PDL is locally monitored on the TX with the proposed adiabatic power sensing, without requiring any power monitoring or dedicated uplink on the RX implant side and achieving high accuracy and low power consumption. Based on the PDL sensing information, the proposed SWP tracking loop enables fast US frequency tuning to achieve maximum PDL. The 3.375mm² 65nm CMOS US powering TX is the first work demonstrating on-chip SWP tracking. With the TX delivering 3.4 mW of acoustic power, SWP tracking can achieve up to 2.7× improvement in PDL, with more than 82% of power tracking accuracy and only 43 μW of power overhead. The SWP tracking loop settles to the frequency that maximizes PDL in less than 90ms, enabling PDL regulation even under powering distance variations caused by fast movements such as the heartbeat.