HDR-DTCP: High-Dynamic-Range Injectable Differential Tissue-Coupled Powering for Thread-Like Battery-Free Wireless Stimulators

Implantable stimulators increasingly demand wireless power, yet prevailing inductive, ultrasonic, magnetoelectric, optical, and mid-field RF links cannot simultaneously achieve high efficiency, alignment robustness, and deep nerve target in a truly needle-deliverable geometry. Strongly frequency and site-dependent tissue impedances, posture-driven coupling shifts, and changing stimulation loads further prevent conventional energy harvesters from maintaining a stable supply. We present High-Dynamic-Range Injectable Differential Tissue-Coupled Powering (HDR-DTCP), a high-frequency body-coupled technique where skin-surface differential electrodes drive AC through tissue and a threadlike implant differentially picks it up for on-chip HDR rectification. Because coupling is distributed over the implant length rather than its cross-section, HDR-DTCP yields length-scalable power transfer efficiency, enabling a thread-like form factor conducive to minimally invasive injection methods that are currently unattainable with coils or laminate or transducer-based approaches. The proposed 65 nm prototype integrates a reconfigurable 4-stage harvester that achieves 63.5% peak power conversion efficiency (PCE) at –16.3 dBm and sustains > 50% PCE over a 9 dB input range, together with a digitally tunable biphasic stimulator capable of driving loads up to RL> 1 kΩ and CL< 20 pF, pointing toward fully injectable neurostimulators.