A CMOS closed-loop miniaturized wireless power transfer system for brain implant applications
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A CMOS closed-loop miniaturized wireless power transfer system for brain implant applications Nishat T. Tasneem1
•
Dipon K. Biswas1 • Ifana Mahbub1
Received: 4 February 2020 / Revised: 25 August 2020 / Accepted: 8 September 2020 Ó Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Near-field inductively coupled wireless power transfer (WPT) system has been extensively utilized for brain implant applications. Still, the efficient and reliable delivery of power is challenging as the received power varies due to different variabilities between the transmitter (TX) and the receiver (RX) coils. A closed-loop adaptive control system utilizing load shift keying, designed in the 0.5 lm standard CMOS process for providing the required power to the implant load compensating for these discrepancies is proposed in this paper. Both the proposed TX and the RX coils are fabricated using FR4 substrate having the dimensions of 10 9 10 mm and 5 9 5 mm, respectively. By changing the supply voltage of the power amplifier, this adaptive closed-loop system regulates the transmitted power to deliver 5.83 mW of power to the load, which is the approximate mid-point of the threshold window. The system achieves power transfer efficiencies of 9% and 8% at 8 mm distance through the air and the tissue media, respectively. Preliminary results show that the miniaturized WPT module with the feedback-loop achieves 8% and 3% of efficiency improvement for 8 mm distance between the TX and the RX coils, compared to the open-loop counterparts. Keywords Adaptive regulation Brain implant Load modulation Threshold window Wireless power transfer
1 Introduction Recent progressions in near-field wireless power transfer (WPT) systems have a significant aspect for applications in implantable medical devices, i.e., optogenetic implants, retinal prosthetics, neural signal recording, deep brain stimulations, etc. [1–4]. This paper focuses on the design of a miniaturized WPT system for brain implant applications. Wirelessly powered brain implant allows avoiding bulky and bio-hazardous batteries and surgeries for replacement [5]. One of the critical aspects of the implantable WPT system is to maintain reliability by continuously providing the required power to the implant. A typical WPT system for an implant includes a receiver (RX) coil with subsequent blocks, i.e. rectifier, low-dropout regulator (LDO) or DC–DC voltage converter, and a load, which might be the sensor circuitry, or l-light-emitting diode (l-LED) for & Nishat T. Tasneem [email protected] 1
optogenetic based neuromodulation application. Achieving a high-power transfer efficiency (PTE) of the system is a challenge as the received power varies due to various constraints. For instance, loose-coupling due to environmental variabilities namely co-axial or lateral displacements, angular misalignment due to the orientation of the inductive link pair, frequency mismatches between the (transmitter) TX and the RX coils, and the variation of the load impedan
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