Critical components in 0.14 THz communication systems

In the super-heterodyne terahertz communication system, the proper design of the critical components like mixers and filters are of great importance for enhancing its performance. In this work, some issues on our newly developed system setup design for 0.14 THz wireless communications and the key components subharmonic mixer (SHM) based on Schottky diode, as well as silicon micromachined bandpass rectangular waveguide filters are presented. According to ADS simulation, the optimum conversion loss of the 140 GHz SHM is around 8.2 dB. And the silicon-micromachined rectangular waveguide filters have been fabricated and the measured lowset insertion losses are lower than 0.5 dB.Comment: 4 pages, 5 figures, 2012 IEEE International Workshop on Microwave and Millimeter Wave Circuits and System Technolog

Compensation technique for nonlinear distortion in RF circuits for multi-standard wireless systems

Recent technological advances in the RF and wireless industry has led to the design requirement of more sophisticated devices which can meet stringent specifications of bandwidth, data rate and throughput. These devices are required to be extremely sensitive and hence any external interference from other systems can severely affect the device and the output. This thesis introduces the existing problem in nonlinear components in a multi-standard wireless system due to interfering signals and suggests potential solution to the problem. Advances in RF and wireless systems with emerging new communication standards have made reconfigurablility and tunability a very viable option. RF transceivers are optimised for multi-standard operation, where one band of frequency can act as an interfering signal to the other band. Due to the presence of nonlinear circuits in the transceiver chains such as power amplifiers, reconfigurable and tunable filters and modulators, these interfering signals produce nonlinear distortion products which can deform the output signal considerably. Hence it becomes necessary to block these interfering signals using special components. The main objective of this thesis is to analyse and experimentally verify the nonlinear distortions in various RF circuits such as reconfigurable and tunable filters and devise ways to minimize the overall nonlinear distortion in the presence of other interfering signals. Reconfigurbality and tunablity in filters can be achieved using components such as varactor diodes, PIN diodes and optical switches. Nonlinear distortions in such components are measured using different signals and results noted. The compensation method developed to minimize nonlinear distortions in RF circuits caused due to interfering signals is explored thoroughly in this thesis. Compensation method used involves the design of novel microstrip bandstop filters which can block the interfering signals and hence give a clean output spectrum at the final stage. Recent years have seen the emergence of electronic band gap technology which has “band gap” properties meaning that a bandstop response is seen within particular range of frequency. This concept was utilised in the design of several novel bandstop filters using defected microstrip structure. Novel tunable bandstop filters has been introduced in order to block the unwanted signal. Fixed single-band and dual-band filters using DMS were fabricated with excellent achieved results. These filters were further extended to tunable structures. A dual-band tunable filter with miniaturized size was developed and designed. The designed filters were further used in the compensation technique where different scenarios showing the effect of interfering signals in wireless transceiver were described. Mathematical analysis proved the validation of the use of a bandstop filter as an inter-stage component. Distortion improvements of around 10dB have been experimentally verified using a power amplifier as device under test. Further experimental verification was carried out with a transmitter which included reconfigurable RF filters and power amplifier where an improvement of 15dB was achieved

Ultra-low power radio transceiver for wireless sensor networks

The objective of this thesis is to present the design and implementation of ultra-low power radio transceivers at microwave frequencies, which are applicable to wireless sensor network (WSN) and, in particular, to the requirement of the Speckled Computing Consortium (or SpeckNet). This was achieved through quasi-MMIC prototypes and monolithic microwave integrated circuit (MMIC) with dc power consumption of less than 1mW and radio communication ranges operating at least one metre. A wireless sensor network is made up of widely distributed autonomous devices incorporating sensors to cooperatively monitor physical environments. There are different kinds of sensor network applications in which sensors perform a wide range of activities. Among these, a certain set of applications require that sensor nodes collect information about the physical environment. Each sensor node operates autonomously without a central node of control. However, there are many implementation challenges associated with sensor nodes. These nodes must consume extremely low power and must communicate with their neighbours at bit-rates in the order of hundreds of kilobits per second and potentially need to operate at high volumetric densities. Since the power constraint is the most challenging requirement, the radio transceiver must consume ultra-low power in order to prolong the limited battery capacity of a node. The radio transceiver must also be compact, less than 5×5 mm2, to achieve a target size for sensor node and operate over a range of at least one metre to allow communication between widely deployed nodes. Different transceiver topologies are discussed to choose the radio transceiver architecture with specifications that are required in this project. The conventional heterodyne and homodyne topologies are discussed to be unsuitable methods to achieve low power transceiver due to power hungry circuits and their high complexity. The super-regenerative transceiver is also discussed to be unsuitable method because it has a drawback of inherent frequency instability and its characteristics strongly depend on the performance of the super-regenerative oscillator. Instead, a more efficient method of modulation and demodulation such as on-off keying (OOK) is presented. Furthermore, design considerations are shown which can be used to achieve relatively large output voltages for small input powers using an OOK modulation system. This is important because transceiver does not require the use of additional circuits to increase gain or sensitivity and consequently it achieves lower power consumption in a sensor node. This thesis details the circuit design with both a commercial and in-house device technology with ultra-low dc power consumption while retaining adequate RF performance. It details the design of radio building blocks including amplifiers, oscillators, switches and detectors. Furthermore, the circuit integration is presented to achieve a compact transceiver and different circuit topologies to minimize dc power consumption are described. To achieve the sensitivity requirements of receiver, a detector design method with large output voltage is presented. The receiver is measured to have output voltages of 1mVp-p for input powers of -60dBm over a 1 metre operating range while consuming as much as 420μW. The first prototype combines all required blocks using an in-house GaAs MMIC process with commercial pseudomorphic high electron mobility transistor (PHEMT). The OOK radio transceiver successfully operates at the centre frequency of 10GHz for compact antenna and with ultra-low power consumption and shows an output power of -10.4dBm for the transmitter, an output voltage of 1mVp-p at an operating range of 1 metre for the receiver and a total power consumption of 840μW. Based on this prototype, an MMIC radio transceiver at the 24GHz band is also designed to further improve the performance and reduce the physical size with an advanced 50nm gate-length GaAs metamorphic high electron mobility transistor (MHEMT) device technology

Optically Controlled Reconfigurable Filtenna

This work is regarding the development of a novel antenna called optically controlled reconfigurable filtenna, which is based on the integration of a broadband printed antenna with a bandpass reconfigurable RF filter. The filter is designed by applying defected microstrip structure (DMS) technique and positioned in printed antenna feeding line in order to keep the same size of the original antenna. The filtenna bandwidth is optically reconfigurable by using two photoconductive silicon switches excited by CW laser at 808 nm. Numerical results rely on independent and switchable operational modes through the 2.4 and 5.1 GHz ISM bands, whereas measurements demonstrate two reconfigurable modes based on single-band/dual-band operation over the same frequency bands. The proposed device is validated by theoretical, numerical, and experimental results

5.75 GHz Microstrip Bandpass Filter for ISM Band

This paper presents on 5.75 GHz bandpass filter based on IEEE802.11a standard for wireless LAN application. The development of bandpass filter includes calculation, simulation, testing and measurement of the filter parameters process has been presented. Simulation software for this project used Ansoft Designer software. The filter operates at center frequency of 5.75 GHz with 100 MHz bandwidth and insertion loss below 10 dB. The bandpass filter contributes to the application of direct conversion front-end receiver for WLAN application at 5.8 GHz frequency

24GHz CMOS direct downconversion receiver front-end and VCO design

Because of advancements in RF CMOS circuits, devices, and passive elements in the last decade, it has become possible to develop a RF system-on-chip (SoC) that integrates RF, analog and digital circuits completely. Direct downconversion, or zero-IF downconversion architecture, shows an advantage over traditional superheterodyne architectures, because it eliminates the image rejection filter and IF filter, and employs only one local oscillator (LO), which reduces the receiver size and power dissipation significantly. For this reason, direct downconversion has drawn more and more attention recently in various wireless applications. However, it also presents some design challenges like flicker noise, DC offsets, even-order distortion, and I/Q mismatches. In this work, a thorough noise analysis and a comprehensive study of the noise mechanism of the low noise amplifier of CMOS direct downconversion receivers (DCR) is given. Also addressed is the design of a cross-coupled LC voltage-controlled oscillator (VCO). For the low noise amplifier, which presents major noise contribution to the DCR front-end, an optimization technique which employs both a parallel capacitance and an inter-stage inductor is proposed. The addition of this capacitance helps keep the active device relatively small, and the analysis on the effects of the inter-stage inductor shows that it helps boost gain of the LNA at the desired operation frequency of 2.4GHz, and offers a lower noise figure. In order to achieve direct downconversion, both a passive switching mixer and an active double-balanced mixer are presented. The passive switching mixer helps solve the problem of flicker noise, but suffers power loss, while the double-balanced architecture helps relieve the problems of DC offset and second-order distortion. The last part of this presentation is about a partially tunable CMOS LC-VCO which achieves good phase noise performance at the cost of smaller tuning range. It uses on-chip spiral inductors and junction varactors in the resonant LC-tank. The presented building blocks can be used for a low-power, low-voltage DCR front-end for 802.11b/g applications. It is concluded that direct downconversion architecture can find its use in low-power, low-cost 802.11b and Bluetooth applications should the circuit design make use of the optimization techniques addressed in this work

Design of Compact Hilbert Microstrip Bandpass Filter For Modern Wireless Communication Systems

This paper presents a new microwave narrow-band bandpass filter with aminiaturized size for use in modern wireless communication systems. Theproposed filter design topology is based on a single-mode microstrip resonatorconstructed in the form of Hilbert fractal geometries from 2nd to 4th iteration levels.The space-filling property the proposed filter topologies possess, has found toproduce reduced size structures corresponding to the successive iteration levels.Many filters have been designed for the Industrial Scientific Medical band (ISMband) applications at a design frequency of 2.4 GHz using a substrate with adielectric constant of 10.8 and thickness of 1.27mm. The performance of each ofthe resulting bandpass filter structures has been analyzed using a method ofmoments (MoM) based software package, Microwave Office 2007, fromAdvanced Wave Research Inc. Results show that these filters possess goodtransmission and return loss characteristics, besides the miniaturized sizes gained;making them the design specifications of most of wireless communication systems