A variable gain RF front-end, based on a Voltage-Voltage feedback LNA, for multistandard applications

Employing feedback circuits in RF front-ends can be a key aspect for easy reconfiguration of multistandard receivers. A narrow-band filter can shape the frequency transfer function and, by reflection due to the feedback network, the input impedance. Switching one single filter component thus allows selecting a different standard. We introduce a voltage-voltage feedback low noise amplifier that, besides being easily reconfigurable, shows roughly the same noise and better linearity, for same power consumption, as the conventional inductively degenerated topology. A direct conversion front-end, including the LNA and I and Q mixers, tailored to WLAN applications in the 5-6 GHz range, has been realized in a 0.25-/spl mu/m SiGe BiCMOS process. Prototypes show the following performances: 2.5 dB NF, 31.5 dB gain, -9.5dBm IIP3, and +23dBm minimum IIP2 while consuming 16 mA from a 2.5 V supply.     

Modulation of Multiscale 3D Lattices through Conformational Control: Painting Silk Inverse Opals with Water and Light

Structural proteins from naturally occurring materials are an inspiring template for material design and synthesis at multiple scales. The ability to control the assembly and conformation of such materials offers the opportunity to define fabrication approaches that recapitulate the dimensional hierarchy and structure–function relationships found in nature. A simple and versatile directed assembly method of silk fibroin, which allows the design of structures across multiple dimensional scales by generating and tuning structural color in large‐scale, macro defect‐free colloidally assembled 3D nanostructures in the form of silk inverse opals (SIOs) is reported. This approach effectively combines bottom‐up and top‐down techniques to obtain control on the nanoscale (through silk conformational changes), microscale (through patterning), and macroscale (through colloidal assembly), ultimately resulting in a controllable photonic lattice with predefined spectral behavior, with a resulting palette spanning almost the entire visible range. As a demonstration of the approach, examples of “multispectral” SIOs, paired with theoretical calculations and analysis of their response as a function of changes of lattice constants and refractive index contrast are illustrated.     

Single-Stage Low-Power Quadrature RF Receiver Front-End: The LMV Cell

This paper presents the first quadrature RF receiver front-end where, in a single stage, low-noise amplifier (LNA), mixer and voltage-controlled oscillator (VCO) share the same bias current. The new structure exploits the intrinsic mixing functionality of a classical LC tank oscillator providing a compact and low-power solution compatible with low-voltage technologies. A 0.13-mum CMOS prototype tailored to the GPS application is presented. The experimental results exhibit a noise figure of 4.8 dB, a gain of 36 dB, an IIP3 of -19 dBm with a total power consumption of only 5.4 mW from a voltage supply of 1.2 V     

Synthesis of amorphous silicon/magnesia based direct opals with tunable optical properties

The effective refractive index of silica based artificial opals can be strongly modulated through magnesiothermic and wet etching processes. The magnesiothermic reduction of silica spheres assembled in a fcc lattice produces amorphous silicon/magnesia matrix, which can be easily converted in oxidized porous silicon, preserving the ordered structure. These results are verified by electron microscopies and IR/Raman spectroscopies. The optical properties are analyzed in terms of the experimental reflectance spectra. By comparing the measured data to rigorous calculations, the good quality of the opaline replicas is demonstrated.     

A 0.13 /spl mu/m CMOS front-end, for DCS1800/UMTS/802.11b-g with multiband positive feedback low-noise amplifier

This paper presents a fully integrated CMOS receiver front-end based on a direct conversion architecture for UMTS/802.11b-g and a low-IF architecture at 100 kHz for DCS1800. The two key building blocks are a multiband low-noise amplifier (LNA) that uses positive feedback to improve its gain and a highly linear mixer. The front-end, integrated in a 0.13 /spl mu/m CMOS process, exhibits a minimum noise figure of 5.2 dB, a programmable gain that can be varied from 13.5 to 28.5 dB, an IIP3 of more than -7.5 dBm and an IIP2 better than 50 dBm. The total current consumption is 20mA from a 1.2V supply.     

Biomaterial‐Based “Structured Opals” with Programmable Combination of Diffractive Optical Elements and Photonic Bandgap Effects

Naturally occurring iridescent systems produce brilliant color displays through multiscale, hierarchical assembly of structures that combine reflective, diffractive, diffusive, or absorbing domains. The fabrication of biopolymer‐based, hierarchical 3D photonic crystals through the use of a topographical templating strategy that allows combined optical effects derived from the interplay of predesigned 2D and 3D geometries is reported here. This biomaterials‐based approach generates 2D diffractive optics composed of 3D nanophotonic lattices that allow simultaneous control over the reflection (through the 3D photonic bandgap) and the transmission (through 2D diffractive structuring) of light with the additional utility of being constituted by a biocompatible, implantable, edible commodity textile material. The use of biopolymers allows additional degrees of freedom in photonic bandgap design through directed protein conformation modulation. Demonstrator structures are presented to illustrate the lattice multifunctionality, including tunable diffractive properties, increased angle of view of photonic crystals, color‐mixing, and sensing applications.     

A 2-D GRO Vernier time-to-digital converter with large input range and small latency

The proposed time-to-digital converter (TDC) arranges two Vernier gated-ring-oscillator (GRO) branches in a 2-dimension (2-D) fashion. All delay differences between X-axis phases and Y-axis phases (based on 2-D definition) can be used, rather than only the diagonal line. The large latency time inherited from Vernier structure is therefore dramatically reduced. The TDC is implemented in a 90 nm CMOS process and consumes 1.8 mA from 1.2 V. The measured input range can safely cover a full period of a 50 MHz sampling signal. With the same delay elements, the latency time is less than 1/6 of that needed in a standard Vernier TDC.     

Broadband light trapping with disordered photonic structures in thin‐film silicon solar cells

We theoretically investigate light trapping with disordered 1D photonic structures in thin‐film crystalline silicon solar cells. The disorder is modelled in a finite‐size supercell, which allows the use of rigorous coupled‐wave analysis to calculate the optical properties of the devices and the short‐circuit current density J_sc. The role of the Fourier transform of the photonic pattern in the light trapping is investigated, and the optimal correlation between size and position disorder is found. This result is used to optimize the disorder in a more effective way, using a single parameter. We find that a Gaussian disorder always enhances the device performance with respect to the best ordered configuration. To properly quantify this improvement, we calculate the Lambertian limit to the absorption enhancement for 1D photonic structures in crystalline silicon, following the previous work for the 2D case [M.A. Green, Progr. Photovolt: Res. Appl. 2002; 10 (4), pp. 235–241]. We find that disorder optimization can give a relevant contribution to approach this limit. Finally, we propose an optimal disordered 2D configuration and estimate the maximum short‐circuit current that can be achieved, potentially leading to efficiencies that are comparable with the values of other thin‐film solar cell technologies. Copyright © 2013 John Wiley & Sons, Ltd.