Yan Chiew Wong

An evaluation of 2-phase charge pump topologies with charge transfer switches for green mobile technology

The development of charge pumps has been motivated by the power supply requirements of portable electronic devices. Charge pumps are inductorless DC-DC converters that are small size and high integration. The quality of the charge pump greatly depends on the effectiveness of switches to turn on and off at the designated clock phases. However, to date, no analysis has been carried out on the overall performance of charge pumps based on switch components in practice. This work demonstrates the characteristics of transistors as charge transfer switches and their effects on the performance of a charge pump. Three most common charge pump topologies are evaluated in terms of voltage drop due to on-resistance and charge loss per switch. Simulations are performed in 0.35µm Austriamicrosystems (AMS) technology for Dickson, Voltage Doubler and Makowski charge pump topologies in steady and dynamic states. In addition, the effect of switch parameters for different charge pump topologies are compared and analysed. We demonstrate that the Makowski charge pump is the topology for future green mobile technology.

Practical design strategy for two-phase step up DC-DC Fibonacci Switched-Capacitor converter

The Fibonacci Switched-Capacitor (SC) converter demonstrates the highest performance by using minimum number of capacitors. However, as the Fibonacci SC requires a wide range of voltage rating of the devices, its implementation is difficult. This paper presents two gate driving techniques for designing and implementing two-phase Fibonacci SC converter for both low and high step-up conversion ratios. The proposed gate driving techniques only require few auxiliary transistors to provide the required boosted voltages for turning the charge transfer switches in the converter on and off. As a result, the proposed gate driving techniques reduce the design complexity and increase the reliability of the Fibonacci SC converter. Practical 8X and 5X Fibonacci SC converters are simulated and constructed based on the proposed techniques. The high conversion efficiencies achieved prove the effectiveness of the proposed techniques.

Efficient ultra-high-voltage controller-based complementary-metal-oxide-semiconductor switched-capacitor DC-DC converter for radio-frequency micro-electro-mechanical systems switch actuation

Achieving wireless connectivity in ever smaller, lower power portable devices with increasing number of features and better radio-frequency (RF) performance is becoming difficult to fulfill through existing RF front-end technology. RF micro-electro-mechanical systems (MEMS) switch technology, which has significantly better RF characteristics than conventional technology and has near-zero power consumption, is one of the emerging solutions for next generation RF front-ends. However, to achieve satisfactory RF MEMS device performance, it is often necessary to have an actuating circuitry to generate high direct current (DC) voltages for device actuation with low power consumption. In this study, the authors present an RF MEMS switch controller based on a switched-capacitor (SC) DC-DC converter in a 0.35 μm CMOS technology. In this design, novel design techniques for a higher output voltage and lower power consumption in a smaller die area are proposed. The authors demonstrate the design of the high-voltage (HV) SC DC-DC converter by using low-voltage transistors and address reliability issues in the design. Through the proposed design techniques, the SC DC-DC converter achieves more than 25% higher boosted voltage compared to converters that use HV transistors. The proposed design provides 40% power reduction through the charge recycling circuit. Moreover, the SC DC-DC converter achieves 45% smaller than the area of the conventional converter.

Meandered inverted-F antenna for MIMO mobile devices

This paper presents an improved efficiency, miniaturized, meandered, inverted F antenna for MIMO systems. A 7.5 mm by 15.5 mm miniature antenna has been developed which gives 25% of improvement for the voltage standing wave ratio compared to the basic IFA structure. The antenna achieves a 10dB return loss over nearly 7% bandwidth at 2.45 GHz. Three antennas were placed on a 110mm × 50 mm ground-plane at a height of 7 mm from ground. The geometry and position of the antennas are optimized in order to achieve the low mutual coupling and small envelope correlation that complies with MIMO requirements. Simulations show that the antenna has high radiation efficiency. A prototype of the system has been fabricated and tested.

Reconfigurable wideband RF impedance transformer integrated with an antenna for multi-band wireless devices

In this paper, we design and implement an ultra wideband antenna using impedance transformer for next generation radio Frequency (RF) front-end. Centre to this, a novel reconfigurable radial stub impedance transformer is proposed to achieve a wideband characteristic for a diverse set of frequency standards. A prototype of the impedance transformer has been fabricated and tested which demonstrates a close match between design simulations and measured results. 4X improvement to the bandwidth and 2X improvement to the return loss are achieved when the proposed impedance transformer is integrated with a narrow bandwidth antenna. The results show that adding the reconfigurable RF transformer can facilitate excellent frequency agility of the return loss of the antenna over other frequency standards. The proposed design technique significantly enhances the system capability to operate with multiple operating frequencies; providing the possibility to realize a reconfigurable RF front-end system.