Qingyun Ma

Power-oscillator based high efficiency inductive power-link for transcutaneous power transmission

Transcutaneous power transmission is a critical issue for long term reliable operation of implantable systems. This paper reports a power-oscillator based inductive power link to power up any implantable unit inside the human body. Instead of using power amplifier which requires high drive requirement, two power-oscillator based inductive powering schemes have been presented to achieve high link efficiency. The first scheme utilizes a class-E power oscillator whereas the second scheme uses a differential cross-coupled power oscillator to drive the inductive link. Resonant inductive link has been used to achieve better link efficiency. Simulation results indicate that for a coupling coefficient of 0.45, the class-E power-oscillator based scheme shows a link efficiency of 66% and the differential cross-coupled power-oscillator based scheme shows more than 90% link efficiency. The system has been designed using 0.5-µm standard CMOS process and both of the systems can handle more than 10 mW of power which is adequate for safe operation of biomedical implants.

A high efficiency inductive power link and backward telemetry for biomedical applications

High-performance wireless power transmission working as a continuous power source of implantable devices can prevent biohazard from leakage of buttery fluid or skin infection from transcutaneous cable. This work reports a high efficiency inductive powering and backward telemetry for implantable medical devices. A new differential class-E type power oscillator with high efficiency excites the external unit, the resonant link coils transfer the power to the internal unit, a modified rectifier circuit rectifies and boosts the recovered signal, and a Zener diode based voltage regulator regulates the output DC voltage. The recovered power is then used to run a ring oscillator-based sensor readout circuit to generate data signal based on sensor current variation and finally a load-shift-keying (LSK) is used to back transit the data to the external unit. The system has been designed using 0.5-µm standard CMOS process with off-chip zener diode, opamp and inductors. The over all power-efficiency of the system is found to be 74.0%.

A low-loss rectifier unit for inductive-powering of biomedical implants

Biomedical implants have been developed in the recent years with a focus for continuous and real-time monitoring of physiological parameters. Battery-less operation of the implanted unit requires energy harvesting from an inductive link or from the neighboring environment. For efficient conversion of harvested energy to a usable DC level, a rectifier block is employed. However conventional CMOS full bridge rectifier incurs a significant amount of power loss and lowers the overall efficiency of the powering system. In this work a cross-coupled MOSFET based LC oscillator structure has been presented as a modified rectifier circuit. Cross-coupled structure minimizes the loss of the MOS switches and LC tank circuit boosts up the output DC level. The rectifier unit has been designed and simulated using 0.5-µm standard CMOS process. For simulation purposes, different biomedical frequency bands are used to validate the effectiveness of the proposed circuit. Simulation results show that the proposed rectifier circuit can achieve 75% PCE compared to the conventional full bridge CMOS rectifier of only 3% PCE.

Ultra-low-power high sensitivity spike detectors based on modified nonlinear energy operator

Spike detectors are important data-compression components for state-of-the-art implantable neural recording microsystems. This paper proposes two improved spike detection algorithms, frequency-enhanced nonlinear energy operator (fNEO) and energy-of-derivative (ED), to solve the sensitivity reduction of a conventional nonlinear energy operator (NEO) in the presence of baseline interference. The proposed methods are implemented in two analog spike detectors with a standard 0.13-μm CMOS process. To achieve an ultra-low-power design, weak-inversion MOSFET based multipliers, adders and derivative circuits are developed to work with a 0.5 V power supply. The power dissipations of the proposed fNEO spike detector and the ED spike detector are 258.7 nW and 129.4 nW, respectively. Quantitative investigations based on the standard deviation and peak-to-clutter ratio of the detected spikes indicate that the proposed spike detector schemes hold higher sensitivity than the conventional NEO based spike detector.

Power-loss reduction of a MOSFET cross-coupled rectifier by employing zero-voltage switching

Ubiquitous monitoring of sensor data and long term reliable operation of sensor units have been studied extensively either for environmental monitoring or for biomedical applications. Long term operation of sensor units requires continuous wireless signal at the output. The proposed rectifier unit is designed and simulated using 0.5-μm standard CMOS process. Simulation results show that power supply from an external source to avoid unwieldy wires or periodic battery replacements. Inductive-power transfer, as a suitable way of driving the sensor electronics, needs a high efficiency rectifier unit to convert the harvested wireless energy into a usable DC level. However, conventional full-wave bridge rectifier with a lower output voltage and a significant power loss lowers the overall efficiency of the inductive-link system. In this paper, a class-E type zero-voltage-switching structure is presented to achieve a high efficiency rectifier circuit. The symmetrical differential class-E switching structures are driven by differential AC signals that result in a low-loss full-wave rectified the proposed rectifier circuit can achieve more than 76% power conversion efficiency for an input AC signal of 7 MHz frequency with signal amplitude of 2 V (peak).

Robust power oscillator design for inductive-power link applications

Microelectronic devices are widely used in biomedical applications such as infusion pumps, artificial organs, dialysis machines, cochlear and dental implants, etc. For continuous operation of implantable medical devices, the implanted units need to be powered up from an external source. Use of implantable batteries poses potential battery fluid leakage and biohazard. Unlike the batteries, wireless power transmission shows better promises for implanted micro devices. Previously reported differential cross-coupled power oscillator based scheme showed more than 90% link efficiency designed in a 0.5-μm standard CMOS process. However, the variation of mutual coupling between the link coils affects the resonance condition and lowers the power-added efficiency of the power oscillator. To make the power oscillator robust, injection-locking mechanism is incorporated with the differential power oscillator. The new injection-locked differential oscillator can lock the frequency with the variation of coupling coefficient by injecting weak differential current signals. Simulation results indicate that with the injection-locking, the oscillation frequency and the power-added efficiency are improved by 4.18% and 24.4%, respectively compared to the regular power oscillator structure for a coupling coefficient of 0.4.

Low-power spike-mode silicon neuron for capacitive sensing of a biosensor

Neuromorphic computation promises to be an energy-efficient information processing technique both for the biological and the real-world environments. In this paper a novel structure of silicon neuron has been designed for measuring the variation of a sensor capacitance. The current-reuse technique and the subthreshold region operation of MOSFETs help achieving ultra-low-power consumption. The proposed silicon neuron is designed and simulated in 0.13-μm standard CMOS technology. The entire unit consists of 43 transistors and consumes only 33 nW with a supply voltage of 1 V. The output frequency is proportional to the variation of the sensor capacitance.

A miniaturized spiral antenna for energy harvesting of implantable medical devices

In this paper, a wireless power transfer system for implantable medical devices using a miniaturized 3 mm diameter single arm circular spiral antenna is presented. The transmission characteristics, S21 between the transmitting and receiving antennas with air and tissue as a medium between antennas are analyzed and measured. The receiver antenna receives almost 2 mW average power with power transfer efficiency of 53%. The power transfer efficiency could still reach to 4% with 274 μW average received power, with placement of 1.5 cm tissue and 1 cm air in between two antennas. With one PN diode rectifier, the total DC power from the receiver side is 489 nW.

Low-loss rectifier for RF powering of implantable biosensing devices

The biochips are considered as one of the promising concepts for in-vivo or in-vitro characterizing or quantifying of biomolecules. The inductive powering can not only maintain the continuous wireless power from the external source for long term operation of implantable biochip to reduce the risk from the battery leakage or skin infection from the connecting wires, but also establish a wireless communication system between the biochip and the external device. A high-efficiency rectifier unit is needed in inductive-power transfer system to convert the received energy into a usable DC voltage. In this paper, a high power-conversion-efficiency differential inductor based class-E type zero-voltage-switching structure is presented to replace the low efficiency conventional full-wave bridge rectifier. The proposed rectifier unit is designed using 0.5-μm standard CMOS process. Simulation results show that the proposed differential rectifier circuit can achieve more than 92% power-conversion-efficiency for an input AC source of 7 MHz frequency with signal amplitude of 2 V (peak).

An ultra-low-power pseudo-random number generator based on biologically inspired chaotic silicon neuron circuit

This work presents an ultra-low-power, biologically inspired pseudo-random number generator based on the Hodgkin-Huxley silicon neuron circuit. The chaotic phenomenon observed in neurons is exploited to generate random numbers. The random sequence generated by the proposed system passed the statistical tests specified by Federal Information Processing Standard. The proposed random number generator circuit provides an ultra-low-power alternative for pseudo-random number generation with 180 nW power consumption.