A Novel Two-Channel Continuous-Time Time-Interleaved 3rd-order Sigma- Delta Modulator with Integrator-Sharing Topology

this paper presents a 3rd-order two-path Continuous-Time Time-Interleaved (CTTI) delta-sigma modulator which is implemented in standard 90nm CMOS technology. The architecture uses a novel method to resolve the delayless feedback path issue arising from the sharing of integrators between paths. By exploiting the concept of the time-interleaving techniques and through the use time domain equations, a conventional single path 3rd-order Discrete-Time (DT) ΔΣ modulator is converted into a corresponding two-path Discrete-Time Time-Interleaved (DTTI) counterpart. The equivalent Continuous-Time Time-Interleaved version derived from the DTTI ΔΣ modulator by determining the DT loop filters and converting them to the equivalent Continuous-Time (CT) loop filters through the use of the Impulse Invariant Transformation. Sharing the integrators between two paths of the reported modulator makes it robust to path mismatch effects compared to the typical Time-Interleaved (TI) modulators which have individual integrators in all paths. The modulator achieves a dynamic range of 12 bits with an OverSampling Ratio (OSR) of 16 over a bandwidth of 10MHz and dissipates only 28mW of power from a 1.8-V supply. The clock frequency of the modulator is 320MHz but integrators, quantizers and DACs operate at 160MHz

A Charge-Depletion Study of an Electrostatic Generator with Adjustable Output Voltage

Micro-scale generators are becoming more popular for harvesting energy to power bio-implantable devices and sensor networks. Most electrostatic generators (ESGs) use constant capacitors as storage or reservoir components in conjunction with a variable capacitor. The main issue with some existing ESG topologies is that these capacitors deplete and discharge over time. This paper studies a typical ESG and derives the charge depletion problem mathematically. Subsequently, a new ESG capable of circumventing this problem is proposed. Closed-form formulas expressing the output voltage and generated power are derived and validated. The proposed ESG harvests 25% of the power that the mechanical energy source generates by actuating the variable capacitor when the maximum-to-minimum capacitance ratio of the variable capacitor is optimized. In the presented case study, the ESG generates 9.75 mW optimally when a variable capacitor with a maximum/minimum capacitance ratio of 39/ $9.75~\mu \text{F}$ is used for energy harvesting from a 1-Hz knee joint movement of a walking person. The overall volume of the ESG is estimated to be 125 mm3, and the variable capacitor is charged to 5 V at its maximum capacitance. A control mechanism and a self-starting circuit are presented for this ESG architecture, which allows it to generate any desired output voltage. This capability can be used to harvest the maximum available kinetic energy and compensate load variations. © 2001-2012 IEEE

Power Efficient Optimization Procedure for Asynchronous Electrostatic Generators

peer reviewedAsynchronous electrostatic generators have the advantage of omitting the control circuit used for synchronizing mechanical movements with electrical switching events, which results in simplified implementation. In this paper, an improved optimization procedure is proposed for this type of electrostatic generator and its performance in responding to different variations during the operation of the harvester is investigated. Power efficiency and simplicity are the main advantages of the proposed procedure, which is verified by simulation. © 2018 IEEE

A Variable-Capacitance Energy Harvester with Miniaturized Inductor Targeting Implantable Devices

peer reviewedMany variable-capacitance energy harvesters employ a large inductor to improve their power efficiency by reducing conduction losses, which is sub-optimal in applications requiring a small form-factor, such as in implants. This paper describes a variable-capacitance harvester that performs optimally using miniaturized inductors. The impact of scaling the inductor on the generated energy of conventional semi-synchronous and fully-synchronous charge-constraint topologies is investigated analytically as well as experimentally. It is shown that the proposed harvester outperforms the semi-synchronous and fully-synchronous charge-constraint harvesters while using very small inductance values. Using two reservoir capacitors to generate energy without requiring large inductors, as well as utilizing a different switching scheme are the main factors contributing to this advantage. Since harvesting energy from slow moving mechanical sources, such as body movements, constitutes a major challenge, all three harvesters are implemented and tested with an actuating frequency as low as 0.5 Hz and for inductance values between 1 uH to 1 mH. The experimental results for sample designs corroborate the analytical expressions and show that to generate optimal harvested energy of the proposed harvester, the semi-synchronous harvester requires a 15.6 times larger inductor. IEE

A performance comparison between synchronous and asynchronous electrostatic harvesters

peer reviewedSynchronous electrostatic harvesters are able to deliver a higher amount of power to electronic devices compared to the asynchronous electrostatic harvesters. However, synchronous generators need a control circuit for synchronising the electrical switching events with the energy source frequency. Asynchronous electrostatic generators have the advantage of omitting this control circuit resulting in a simplified implementation and eliminates the power consumption related to this part. In this paper, the performance of a typical circuit based on each structure is explored and the optimal parameters for the asynchronous circuit are presented. It is shown mathematically and verified in simulation that the maximum generated power in the asynchronous circuit is equal to 50% of the generated power in the synchronous circuit considering the conduction losses. © 2019 IEEE