Maria Theresa de Leon

Comparison of LNA Topologies for WiMAX Applications in a Standard 90-nm CMOS Process

This paper presents the design of low-noise amplifiers intended for WiMAX applications. Three low-noise amplifier topologies are implemented namely: (1) cascoded common-source amplifier, (2) folded cascode amplifier, and (3) shunt feedback amplifier. The amplifiers were implemented in a standard 90-nm CMOS process and were operated with a 1-V supply voltage. Low-noise amplifier measurements were taken for parameters such as power gain, noise figure, input matching, output matching, reverse isolation, stability, and linearity. Based on the employed figure-of-merit, the cascoded common-source low-noise amplifier achieved the best performance among the three with a simulated gain of 13.8 dB and noise figure of 1.7 dB, which makes it comparable to previously published works.

Solar thermoelectric generators fabricated on a silicon-on-insulator substrate

Solar thermal power generation is an attractive electricity generation technology as it is environment-friendly, has the potential for increased efficiency, and has high reliability. The design, modelling, and evaluation of solar thermoelectric generators (STEGs) fabricated on a silicon-on-insulator substrate are presented in this paper. Solar concentration is achieved by using a focusing lens to concentrate solar input onto the membrane of the STEG. A thermal model is developed based on energy balance and heat transfer equations using lumped thermal conductances. This thermal model is shown to be in good agreement with actual measurement results. For a 1 W laser input with a spot size of 1 mm, a maximum open-circuit voltage of 3.06 V is obtained, which translates to a temperature difference of 226 °C across the thermoelements and delivers 25 µW of output power under matched load conditions. Based on solar simulator measurements, a maximum TEG voltage of 803 mV was achieved by using a 50.8 mm diameter plano-convex lens to focus solar input to a TEG with a length of 1000 µm, width of 15 µm, membrane diameter of 3 mm, and 114 thermocouples. This translates to a temperature difference of 18 °C across the thermoelements and an output power under matched load conditions of 431 nW.This paper demonstrates that by utilizing a solar concentrator to focus solar radiation onto the hot junction of a TEG, the temperature difference across the device is increased; subsequently improving the TEGs efficiency. By using materials that are compatible with standard CMOS and MEMS processes, integration of solar-driven TEGs with on-chip electronics is seen to be a viable way of solar energy harvesting where the resulting microscale system is envisioned to have promising applications in on-board power sources, sensor networks, and autonomous microsystems.

Design and implementation of passive RF-DC converters for RF power harvesting systems

In RF energy harvesting scheme, the acquired voltage level is too low to be considered as a supply voltage of applications such as microsensors. Therefore, there is a need to increase this value, and passive voltage multiplier is a solution to this requirement. In this project, two passive voltage multipliers, namely, Modified Dickson (MDVM) and Mandal-Sarpeshkar (MSVM) voltage multipliers are designed and implemented. From a mere input power of 10µW to 60µW at 13.56MHz, the voltage multipliers effectively increased the output voltage to 905mV to 2.128V and 1.114V to 3.609V for MDVM and MSVM, respectively, given a supply voltage of 1V and a capacitive load of 30pF. All designs are implemented using 90nm CMOS process.

Large Gauge Factor of Hot Wire Chemical Vapour Deposition In-Situ Boron Doped Polycrystalline Silicon

Polysilicon piezoresistors with a large longitudinal gauge factor (GF) of 44 have been achieved using in-situ boron doped hot-wire chemical vapour deposition (HWCVD). This GF is a consequence of a high quality p-type doped polysilicon with a crystal volume of 97% and an average grain size of 150 nm, estimated using Raman spectroscopy and atomic force microscopy (AFM) respectively. The measured minimum Hooge factor associated to the 1/f noise of the polysilicon piezoresistors is 1.4 × 10−3. These results indicate that HWCVD polysilicon is a suitable piezoresistive material for micro-electro-mechanical systems (MEMS) applications.

Active balun circuits for WiMAX receiver front-end

In this paper, three active balun circuits were designed and implemented in a standard 90nm CMOS process namely: (1) common-gate with common-source; (2) differential; and (3) common-source/drain. The active balun designs were intended for Worldwide Interoperability for Microwave Access (WiMAX) applications operating at frequency 5.725–5.825GHz. Measurements were taken for parameters such as gain difference, phase difference, and noise figure. All designs achieved gain difference of less than 1.8dB, phase difference of 180°±10°, and noise figure of around 7.5×12.4dB, which are comparable to previous researches. Low power consumption of at most 3.6mW was achieved.

A 3rd Order Butterworth Gm-C Filter for WiMAX Receivers in a 90nm CMOS Process

This paper presents a design of a 3rd order Butterworth Gm-C Low Pass Filter (LPF) for WiMAX receivers in a 90nm CMOS process. Due to its robustness to process parameter tolerances, a passive LC-ladder filter was emulated using the Signal Flow Graph (SFG) method. As a building block for the LPF, a highly linear operational transconductance amplifier (OTA) based on bias-offset cross-coupled differential pairs was designed and characterized. With this OTA’s property of having its transconductance linearly controlled by a DC voltage bias, the corner frequency of the filter can be externally tuned to achieve the WiMAX specifications for bandwidth. From layout simulations, the LPF achieved a bandwidth of 10MHz at 0.5V DC bias, under a 1V supply. HD2 at 50mV peak, 1KHz input is -40.38dBc. With the addition of a source follower at the output, the filter attained good output matching, with an S22 of -16.45dB. The total power dissipation is 5.26mW.

System-level simulation and analysis of a WiMAX direct-conversion receiver in 90nm CMOS

In this paper, different system-level issues involved in the design of the analog front-end of a direct-conversion receiver are investigated using Agilent Advanced Design System 2009 (ADS 2009). The receiver is designed to target Worldwide Interoperability for Microwave Access (WiMAX), which has been rapidly gaining momentum as an alternative to cable and DSL in delivering wireless broadband access to end-users. The receiver is designed to operate in the unlicensed frequency band from 5.725 to 5.825 GHz with a total noise figure of 6.398 dB, a third-order input-referred intercept point at 5.567 ilBm, 1-dB compression point at −4.433 dBm and a total power gain of 40dB. High-level design trade-offs within the direct-conversion receiver architecture are investigated to characterize the effect of each block in the whole systems performance. A systematic top-down design flow is developed, that would further improve subsequent efforts to design a fully integrated wireless 90nm CMOS transceiver.