An On-/Off-Time Sensing-Based Load-Adaptive Mode Control of Triple Mode Buck Converter for Implantable Medical Devices.

Wireless power transfer (WPT) technology applied to implantable medical devices (IMDs) significantly reduces the need for battery replacement surgery health conditions. This paper presents an on-/off-time sensing-based load-adaptive mode control of triple mode buck converter for implantable medical devices; the converter can adjust the control mode for low power consumption and achieve high power conversion efficiency (PCE) under a small active area. The three modes in the proposed system are the pulse width modulation (PWM), pulse frequency modulation (PFM), and ultra-low power (ULP) modes. The on-time sensor can be used to adjust the system from PWM to PFM modes, and the off-time sensor can be used to adjust the system from PFM to ULP modes. It is fabricated using TSMC 0.18 µm CMOS technology. The input voltage lies in the range 2.2-5.0 V, the output voltage is 1.8 V, and the load current lies in the range 0.05-200 mA (x4000). The experimental results demonstrate the seamless mode transition under the step up/down load transient response. The peak PCE is approximately 94.3% at the 80 mA and the minimum PCE is approximately 65.4% within the load current range.

A 13.56 MHz Wireless Power Transfer System With Fully Integrated PLL-Based Frequency-Regulated Reconfigurable Duty Control for Implantable Medical Devices.

In this paper, a 13.56 MHz wireless power transfer system with transmitter (TX) and receiver (RX) chips is presented. Both TX and RX chips were designed with fully integrated reconfigurable single power stage to realize adaptive power delivery and output voltage regulation. The reconfigurable operation of TX and RX is synchronized and the reconfiguration frequency which could vary with coupling or loading condition is locked by the proposed phase-locked-loop-based on-time duty controller to mitigate the electromagnetic interference. In addition, calibrations for circuit delay and power switch size were implemented in the RX chip to enhance system efficiency further. The system complexity is reduced considerably by removing the successive power stages and off-chip controllers used in previous studies. The TX and RX chips were fabricated in TSMC 0.18 µm CMOS process. The measurement results demonstrated seamless output voltage regulation under an output power range from 4.2 mW to 162 mW and a peak end-to-end efficiency of 70.1%.

A 6.78 MHz, 95.0% Peak Efficiency Monolithic Two-Dimensional Calibrated Active Rectifier for Wirelessly Powered Implantable Biomedical Devices.

In this paper, a fully integrated active rectifier with triple feedback loops is proposed to enhance power conversion efficiency (PCE) over a wide loading range by calibrating both the gate transition timing and power switch size. The on- and off-transitions of the power switches are calibrated using a hybrid delay-based gate control circuit (HDGCC) with hybrid feedback loops. Conventional active rectifiers that only focused on calibrating the gate transition timing of a NMOS power switch with a fixed power switch size exhibit a low PCE when the loading condition deviates from the predetermined range. Thus, an automatic size selector based on a third feedback loop is proposed, which changes the power switch size based on the loading condition and ensures a stable operation of the hybrid loops by maintaining the voltage drop across the NMOS switches. An active rectifier was fabricated using the standard 0.18 µm CMOS process. The effectiveness and robustness of the two-dimensional calibration were verified through measurements under an AC input voltage ranging from 2.5 to 5.0 V and an output power ranging from 1.25 to 125 mW. The peak voltage conversion ratio and peak PCE were 97.6% and 95.0%, respectively, at RL = 500 Ω.

Wearable, wireless gas sensors using highly stretchable and transparent structures of nanowires and graphene.

Herein, we report the fabrication of a highly stretchable, transparent gas sensor based on silver nanowire-graphene hybrid nanostructures. Due to its superb mechanical and optical characteristics, the fabricated sensor demonstrates outstanding and stable performances even under extreme mechanical deformation (stable until 20% of strain). The integration of a Bluetooth system or an inductive antenna enables the wireless operation of the sensor. In addition, the mechanical robustness of the materials allows the device to be transferred onto various nonplanar substrates, including a watch, a bicycle light, and the leaves of live plants, thereby achieving next-generation sensing electronics for the 'Internet of Things' area.