Zohaib Hameed

Hybrid Forward and Backward Threshold-Compensated RF-DC Power Converter for RF Energy Harvesting

This paper presents a hybrid forward and backward threshold voltage compensated radio-frequency to direct current (RF-to-DC) power conversion circuit for RF energy harvesting applications. The proposed circuit uses standard p-channel metal-oxide semiconductor transistors in all the stages except for the first few stages to allow individual body biasing eliminating the need for triple-well technology in the previously reported forward compensation schemes. Two different RF-DC power conversion circuits, one optimized to provide high power conversion efficiency (PCE) and the other to produce a large output DC voltage harvested from extremely low input power levels, are designed and fabricated in IBMs 0.13 μm complementary metal-oxide-semiconductor technology. The first circuit exhibits a measured maximum PCE of 22.6% at -16.8 dBm (20.9 μW) and produces 1 V across a 1 MΩ load from a remarkably low input power level of -21.6 dBm (6.9 μW) while the latter circuit produces 2.8 V across a 1 MΩ load from a peak-to-peak input voltage of 170 mV achieving a voltage multiplication ratio of 17. Also, design strategies are developed to enhance the output DC voltage and to optimize the PCE of threshold voltage compensated voltage multiplier.

A 3.2 V –15 dBm Adaptive Threshold-Voltage Compensated RF Energy Harvester in 130 nm CMOS

This paper presents an adaptive RF-DC power converter designed to efficiently convert RF signals to DC voltages utilizing auxiliary transistors to control the threshold voltage of the transistors in the main rectifier chain dynamically. The proposed circuit passively reduces the threshold voltage of the forward-biased transistors to increase the harvested power and the output voltage and increases the threshold voltage of the reverse-biased transistors to reduce the leakage current to prevent the loss of previously stored energy. A 12-stage adaptive threshold-compensated rectifier is designed and implemented in IBMs 0.13 μm CMOS technology. The proposed rectifier exhibits measured maximum power conversion efficiency (PCE) of 32% at -15 dBm (32 μW) of input power while delivering 3.2 V to a 1 M Ω load. At a remarkably low input power of -20.5 dBm (8.9 μW) for a 1 M Ω load, the rectifier produces an output voltage of 1 V.

Edge detection using histogram equalization and multi-filtering process

Edge detection plays a critical role in image processing. The performance of an edge detection algorithm can be affected by serious noise & intensity inhomogeneities. In this paper, a method aiming at detecting edge of image with varieties of gradient signal degradation is proposed. The method comprises two steps. The first step is to perform adaptive histogram equalization to improve the signal contrast in a discriminative manner. To this end, the histogram of the input image is analysed and the irregularity of image intensity, if there is any, is identified and removed by using a contrast limited adaptive histogram equalization technique. The following step is a gradient modulation filtering process with the modulation factor determined by the local intensity. The simulation results comprising subjective and objective analysis show that the proposed method is applicable and effective to detect edges of low-quality images.

Fully-integrated passive threshold-compensated PMOS rectifier for RF energy harvesting

This paper presents an RF-DC rectifier for radio frequency energy harvesting applications. The proposed passive multi-stage RF-DC rectifier uses standard PMOS transistors to allow individual bulk biasing without the requirement of deep nwell technology. The RF-DC conversion circuit is based on passive threshold self-compensated topology. A design strategy to enhance the input voltage range and to optimize the power conversion efficiency is presented. Designed and simulated in IBM 130-nm CMOS technology, the proposed 915-MHz rectifier shows improved output voltage and power conversion efficiency compared to recent works. When driving a 1-MΩ load, the RF-DC power conversion unit is able to supply 1-V output with an input power of -22 dBm (6.3 μW) and obtains an efficiency of 11.4% at -16.1 dBm (24.5 μW) while supplying 2-V to the output.

Design of impedance matching circuits for RF energy harvesting systems

This paper presents a systematic design methodology for impedance matching circuits of an RF energy harvester to maximize the harvested energy for a range of input power levels with known distribution. Design of input matching networks for RF rectifier differs from those for traditional RF circuits such as low-noise amplifier because the transistors in the RF rectifiers operate in different regions. In this work, it is shown that the input impedance of the rectifier estimated based on small signal simulation of transistors at the peak of input signal in the rectifier when the transistors are biased with stable DC operating voltage provides the largest harvested energy from a fixed input power. For variable input power levels, a matching network selection strategy is proposed to maximize expected harvested energy given the probability density distribution of input power levels. As an experimental sample, an RF energy harvester circuit is designed to maximize the harvested energy in the 902928MHz band employing an off-chip impedance matching circuit designed using the proposed methodology. The proposed RF energy harvester exhibits a measured maximum power conversion efficiency (PCE) of 32% at 15dBm (32W) and delivers an output DC voltage of 3.2V to a 1M load.

Contrast enhancement by adaptive mapping function with local information

Real scenes usually have a wider dynamic range than that of image acquisition devices, which makes most of the image acquired in under/over exposed conditions. Although the existing contrast enhancement algorithms such as contrast limited adaptive histogram equalization (CLAHE) are capable of restoring some of the details degraded in the acquisition, they may fail to detect others. This is mainly due to the complex degradation cases. It is necessary that any new mapping function should be modulated according to the local information. On this line, a new algorithm based on the CLAHE is proposed in this paper. The image quality improvement is focused on the enhancement of the local contrast in an image, in which the signal degradation could result in homogeneous sections in its histogram. It is achieved by discriminative clipping of the pixels based on its intensity levels and redistributing the pixels to maximize the available dynamic range. The contrast enhancement is performed locally based on the information of the local pixels. The clipped pixels are redistributed more assertively near histogram peaks to improve the image quality subjectively with maximum local contrast enhancement. The simulation result shows that the proposed method significantly enhances the image quality.