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.
A new scheme is proposed for real-time multi-joint motion tracking using an on-body sensor network based on frequency-division multiplexed (FDM) magnetic induction (MI). The system employs wearable wireless sensor nodes that extract spatial information from measured node-to-node magnetic coupling. Unlike camera- or accelerometer-based motion-tracking approaches, the MI-based method does not require line of sight and does not accumulate errors due to sensor drift. A custom MI transceiver chip, fabricated in a standard bulk Complementary Metal Oxide Semiconductor (CMOS) process, drives a wearable coil and simultaneously measures tones transmitted by other nodes in full-duplex operation. The chip integrates a fully custom digital signal processor for real-time data analysis and supports a configurable capture rate of up to 977 frames per second. The system is experimentally validated using a 3D printed two-joint leg model and on-body demonstrations, and benchmarked against an open-source camera-based human pose estimation pipeline, demonstrating fully wireless, real-time MI-based motion tracking.
Temporal interference stimulation (TIS) has emerged as a promising neuromodulation technique for achieving deep brain stimulation (DBS) with reduced invasiveness. However, conventional transcutaneous TIS suffers from the current shunting effect from the scalp, which limits the electric-field (E-field) delivery to the target region. In addition, conventional sine-based TIS systems rely on noise-sensitive and linearity constrained analog waveform synthesizers. To address these limitations, this work presents a minimally invasive square-based TIS integrated circuit (IC) that simultaneously achieves enhanced E-field delivery and fully digital stimulation waveform generation. The system generates temporal interference (TI) envelopes by digitally controlling an ON/OFF H-bridge driver, significantly simplifying circuit implementation with a gate-driving overhead of only 250 nW per channel. It also delivers higher root-mean square (RMS) energy than sine-based TIS under identical peak-current conditions. The stimulation IC is integrated within a 0.96 mm2 active area. Experimental tissue phantom measurements show that the proposed system achieves a 2.01 dB higher PSD at Δf and a time-domain envelope amplitude approximately 1.27 times that of sine-based TIS, demonstrating enhanced Δf envelope delivery. The proposed system supports long-term operation (1 s-1 h) and real-time parameter control through an inductive-link interface. It also achieves one of the lowest reported system complexities. These results demonstrate the feasibility of a programmable wireless TIS system for the proposed minimally invasive on-skull configuration.
Conventional wireless approaches for wearable body sensor networks suffer from body shadowing effects and high power consumption. Human body communication (HBC) utilizing the body's conductive properties offers a promising alternative but faces challenges from dynamic channel characteristics and environmental interference coupling in the sub-10 MHz electro-quasi-static (EQS) regime. To mitigate interference effects, existing transceivers employ narrowband operation with conservative carrier-to-data-rate ratios. This paper presents an interference-aware adaptive frequency hopping (AFH) HBC transceiver operating below 10 MHz, where AFH is realized as interference-driven adaptive channel selection. The proposed AFH on-off keying (OOK) transceiver integrates a tiny on-chip microcontroller unit (MCU) enabling autonomous frequency hopping control, real-time channel assessment, and direct sensor interfacing. Fabricated in 65-nm CMOS occupying 0.117 mm2, the transceiver achieves 22-360 kbps data rates, -33 dB signal-to-interference ratio (SIR) tolerance at bit error rate (BER) of 10-3, and 40× BER improvement over single-frequency operation at maximum body distance of 180 cm. The transceiver achieves 62.2-79.5 pJ/bit energy efficiency, enabling extended battery life for distributed wearable applications, while benefiting from the inherent security of the sub-10 MHz EQS regime.
High-performance neuromodulators make essential contributions to the treatment of major neurological disorders and quality of life improvement. To enhance therapeutic efficacy and address safety challenges associated with long-term implanted neuromodulators, several high-performance techniques are proposed in this work. Firstly, a novel redundant current mapping (RCM) technology is developed to improve stimulation resolution at minimal area cost. Secondly, a new power-efficient self-adaptive pulse-width calibration (SAPCA) charge-balancing (CB) scheme ensures long-term stimulation safety. Thirdly, several compliance-extension techniques have been developed to achieve a voltage compliance of±11 V. The ASIC is fabricated in a 180-nm Bipolar-CMOS-DMOS (BCD) process with an area of 0.285 mm2/ch. Measurement results show that it achieves 14.5-bit resolution over a 6.5-mA current range and 12.8-bit resolution over a 10-mA current range. The residual voltage (Vres) is reduced from several V to ±5 mV consuming 1.74 μW. Besides, an in vivo experiment demonstrates that the ASIC can maintain CB under long-term stimulation, thereby preserving chronic neuromodulation safety.
