A Sub-500 mu W Interface Electronics for Bionic Ears

This paper presents an ultra-low power current-mode circuit for a bionic ear interface. Piezoelectric (PZT) sensors at the system input transduce sound vibrations into multi-channel electrical signals, which are then processed by the proposed circuit to stimulate the auditory nerves consistently with the input amplitude level. The sensor outputs are first amplified and range-compressed through ultra-low power logarithmic amplifiers (LAs) into AC current waveforms, which are then rectified through custom current-mode circuits. The envelopes of the rectified signals are extracted, and are selectively sampled as reference for the stimulation current generator, armed with a 7-bit user-programmed DAC to enable patient fitting (calibration). Adjusted biphasic stimulation current is delivered to the nerves according to continuous inter-leaved sampling (CIS) stimulation strategy through a switch matrix. Each current pulse is optimized to have an exponentially decaying shape, which leads to reduced supply voltage, and hence similar to 20% lower stimulator power dissipation. The circuit has been designed and fabricated in 180nm high-voltage CMOS technology with up to 60 dB measured input dynamic range, and up to 1 mA average stimulation current. The 8-channel interface has been validated to be fully functional with 472 mu W power dissipation, which is the lowest value in the literature to date, when stimulated by a mimicked speech signal

A 180 nm Self-Powered Rectifier Circuit for Electromagnetic Energy Harvesters

This paper presents a new self-powered low voltage rectifier implementation for vibration-based electromagnetic (EM) energy harvesters. The proposed circuit is an improved version of the previously reported rectifier, which was designed in TSMC 90 nm CMOS technology. The circuit is designed in lower cost UMC 180 nm CMOS technology, and uses a passive AC/DC quadrupler structure to supply the external power of the utilized active components. Simulation results show that the maximum power conversion efficiency of the circuit is 94% with 500 mV input peak voltage and 8 k Omega load resistance. Lower than 4 mV voltage drop is achieved for input peak voltage above 200 mV at open-load condition. The circuit is able to operate with low frequency input signals, which are commonly available from electromagnetic vibration energy harvesters

Optimized Electromagnetic Harvester with a Non-Magnetic Inertial Mass

This paper presents an optimization study to decrease the operation frequency and increase the output power of a miniature electromagnetic (EM) energy harvester, by incorporating a non-magnetic inertial mass together with the moving magnet. The harvester coil position has been optimized through FEM, and validated through tests. Experimental studies on the inertial mass showed that increasing the magnet size further increases the resonance frequency due to the increased magnetic forces. Conversely, using a non-magnetic mass over the magnet effectively decreases the resonance frequency (27 Hz to 15 Hz), and increases the generated output power. The power output during operation at even lower frequencies is also improved by adding the non-magnetic mass. The optimized 6 cm3 harvester generates 0.45 Vrms and 110 μWrms output power at 15 Hz and 0.7 g peak acceleration

Stage Optimization in Regulated Step-Up for Low Voltage Electromagnetic Energy Harvesters

This paper presents a performance enhancement feature for a novel power management circuit to generate 1.8 V from the low DC voltage rectified at the output of the vibration-based electromagnetic (EM) energy harvesters. The proposed 180 nm circuit utilizes a low voltage charge pump based boost converter with variable output-stages, and an autonomous regulator circuit with negative feedback topology. 2 and 3 stage charge pump options in the variable stage configuration has been validated to extend the supported input voltage range at the same load, or alternatively maintain higher efficiency operation at a higher load range. The simulation results showed that under no-load condition the output voltage reached to 1.8 V for input voltage of 0.65 V and 0.48 V with 2 and 3 stage outputs, respectively. The power conversion efficiency of the power management circuit can be kept stable around 55% by switching from 2 to 3 stages after 3.5 mu A

A 180 nm self-powered rectifier circuit for electromagnetic energy harvesters

This paper presents a new self-powered low voltage rectifier implementation for vibration-based electromagnetic (EM) energy harvesters. The proposed circuit is an improved version of the previously reported rectifier, which was designed in TSMC 90 nm CMOS technology. The circuit is designed in lower cost UMC 180 nm CMOS technology, and uses a passive AC/DC quadrupler structure to supply the external power of the utilized active components. Simulation results show that the maximum power conversion efficiency of the circuit is 94% with 500 mV input peak voltage and 8 k Omega load resistance. Lower than 4 mV voltage drop is achieved for input peak voltage above 200 mV at open-load condition. The circuit is able to operate with low frequency input signals, which are commonly available from electromagnetic vibration energy harvesters

Highly Integrated 3 V Supply Electronics for Electromagnetic Energy Harvesters With Minimum 0.4 V-peak Input

This paper presents a self-powered interface enabling battery-like operation with a regulated 3 V output from ac signals as low as 0.4 V-peak, generated by electromagnetic energy harvesters under low frequency vibrations. As the first stage of the 180 nm standard CMOS circuit, harvested signal is rectified through an ac/dc doubler with active diodes powered internally by a passive ac/dc quadrupler. The voltage is boosted in the second stage through a low voltage charge pump stimulated by an on-chip ring oscillator. The output is finally regulated to 3 V at the last stage. The voltage doubling rectification stage deviates by less than 40 mV from ideal expectation for the validated 0.15-1 V input voltage range. The full system delivers 3 V output to 4.4 M Omega load for input voltage of 0.4 V-peak, which is the lowest operable input voltage in the literature. The demonstrated system generates 9 mu W of dc power with 3 V stable output for 32 mu W input, whereas the circuit is able to supply even more output power for higher input power levels. The maximum efficiency of the rectification stage is 86%, while the full system efficiency is 37% and 28% for unregulated and regulated operation, respectively, when interfaced to an in-house electromagnetic energy harvester under 8 Hz 0.1 g vibration

A Self-Powered and Efficient Rectifier for Electromagnetic Energy Harvesters

This paper presents an interface circuit for efficient rectification of voltages from electromagnetic (EM) energy harvesters operating with very low vibration frequencies. The interface utilizes a dual-rail AC/DC doubler which benefits from the full cycle of the input AC voltage, and minimizes the forward bias voltage drop with an active diode structure. The active diodes are powered through an AC/DC quadrupler with diode connected (passive) transistors. The interface system has been validated to drive 22 mu A load at 1.1 V, with 86% efficiency, when 0.1g vibration is applied to an in house energy harvester at 8 Hz. The circuit is functional down to 150 mV input. The rectified voltage deviates at most 38 mV from the theoretical value of twice the input peak voltage. The system was demonstrated for feasibility in portable applications through a prototype placed to the waist of a jogger

Charge Balance Circuit for Constant Current Neural Stimulation with Less than 8 nC Residual Charge

Charge balancing is a major concern in functional electrical stimulation. Any excess charge accumulation over time leads to electrolysis with the electrode dissolution and tissue destruction. Therefore, charge balance circuits are used for mitigating the effects of charge accumulation in tissues. This work introduces an active synchronous charge balance circuit for constant current neural stimulators that operates without requiring negative supply for remaining charge detection. The charge balance circuit detects the residual charge by monitoring the electrode voltages just before the stimulation. If the voltage difference between the electrodes is above a certain threshold, a balance current is generated to achieve net zero charge at the electrode. Balancing current and the main stimulation current are injected simultaneously, preventing any interference in other electrodes. The charge balance circuit is dynamically disabled to reduce the system power when the charge detection is not active. The circuit can operate for the stimulation currents up to 1.4 mA and hold the electrode charge under 8 nC/phase while consuming only 6.36 µW power