Hamid Nejati

A prototype hardware for random demodulation based compressive analog-to-digital conversion

In this paper, we utilize recent advances in compressive sensing theory to enable signal acquisition beyond Nyquist sampling constraints. We successfully recover signals sampled at sub-Nyquist sampling rates by exploiting additional structure other than bandlimitedness. We present a working prototype of compressive analog-to-digital converter (CADC) based on a random demodulation architecture. The architecture is particularly suitable for wideband signals that are sparse in the time-frequency plane. CADC has the advantage of enhancing the performance of communication and multimedia systems by increasing the transmission rate for the same bandwidth. We report successful reconstruction of AM modulated signals at sampling rates down to 1/8 of the Nyquist-rate, which represents an up to 87.5% savings in the bandwidth and the storage memory.

Modeling and design methodology for metal-insulator-metal plasmonic Bragg reflectors

In this paper, we present a modeling and design methodology based on characteristic impedance for plasmonic waveguides with Metal-Insulator-Metal (MIM) configuration. Finite-Difference Time-Domain (FDTD) simulations indicate that the impedance matching results in negligible reflection at discontinuities in MIM heterostructures. Leveraging the MIM impedance model, we present a general Transfer Matrix Method model for MIM Bragg reflectors and validate our model against FDTD simulations. We show that both periodically stacked dielectric layers of different thickness or different material can achieve the same performance in terms of propagation loss and minimum transmission at the central bandgap frequency in the case of a finite number of periods.

On the feasibility of hardware implementation of sub-Nyquist random-sampling based analog-to-information conversion

In this paper, we successfully demonstrate the feasibility of hardware implementation of a sub-Nyquist random- sampling based analog to information converter (RS-AIC). The RS-AIC is based on the theory of information recovery from random samples using an efficient information recovery algorithm to compute the spectrogram of the signal. Our RS-AIC enables sub-Nyquist acquisition and processing of wideband signals that are sparse in a local Fourier representation. Results from our RS-AIC hardware implementation demonstrate successful reconstruction of signals that are sampled at half the Nyquist-rate while maintaining up to a 51 dB signal-to-noise ratio (SNR), which is equivalent to an 8.5 bit resolution analog to digital converter.

Increasing Manufacturing Yield for Wideband RF CMOS LNAs in the Presence of Process Variations

In this paper, the authors develop several design techniques for reducing the impact of manufacturing variations on integrated wideband low noise amplifiers (LNA). Utilizing an efficient modeling and automated design methodology, the authors investigate the sensitivity of LNA performance metrics to process variations and determine that the input impedance matching is particularly sensitive to perturbations in component values. Based on the sensitivity analysis, the authors leverage several design techniques to increase the reliability of LNA designs. To mitigate the impact of process variations on the input impedance matching, the authors add additional circuit elements and tunable capacitors to dynamically compensate for manufacturing variations after fabrication. The results indicate that the proposed design techniques can increase manufacturing yield by up to one order of magnitude for input impedance matching with only a 14% increase in noise figure

Numerical Design Optimization Methodology for Wideband and Multi-Band Inductively Degenerated Cascode CMOS Low Noise Amplifiers

In this paper, we develop a systematic design optimization methodology for inductively degenerated cascode CMOS low noise amplifiers (LNA) in fully integrated wideband and multi-band wireless systems. Leveraging an accurate analytical circuit model, we combine global and local numerical optimization techniques in a hierarchical manner to simultaneously determine the fixed and switchable passive component and device parameters in the LNA circuit necessary to meet user-specified performance requirements. To demonstrate the effectiveness of proposed design optimization methodology, we utilize the method to create 3 wideband and 3 multi-band LNA designs that meet a wide-range of impedance matching, noise figure, gain, power dissipation, and linearity requirements. The proposed method provides circuit designers with a fast and effective means for the rapid prototyping and design space exploration of wideband and multi-band inductively degenerated cascode CMOS LNAs.

Design of a maximally flat optical low pass filter using plasmonic nanostrip waveguides

In this paper, we present a new optical range low pass filter based on plasmonic nanostrip waveguides. We calculate the characteristic impedance of plasmonic nanostrip waveguides and compare it with that of microstrip transmission lines. An optical range maximally flat low pass filter with subwavelength dimensions is designed based on the nanostrip waveguide structure. Finite-difference time-domain (FDTD) simulations of the designed optical range filter are presented, which demonstrate subwavelength light confinement as well as acceptable filter cutoff performance.

Modeling and Design of Ultrawideband Low Noise Amplifiers with Generalized Impedance Matching Networks

In this paper, we present a complete modeling methodology for fully integrated inductively degenerated cascode ultrawideband low noise amplifiers (LNA) with generalized filter-based impedance matching networks. Our accurate analytical models capture the impact of device and passive component parasitics and transistor short channel effects to closely match circuit simulation results. Utilizing our method, we are able to accurately generate an ultrawideband LNA in the 3.1 to 10.6 GHz band using third and fifth order Chebyshev filters as input matching networks. Both of the designs achieve a power gain greater than 9dB, input and output impedance matching less than -9dB, and a noise figure from less than 3.4dB when using a TSMC 0.18mum mixed-signal/RF model. The performance parameters for the third order filter configuration exceed the results reported from previous ultrawideband designs.

On the design of customizable low-voltage common-gate LNA-mixer pair using current and charge reusing techniques

Given the fast growth of battery-powered wireless communication devices, developing customizable low-voltage low-noise amplifiers (LNAs) and mixers has become a crucial design consideration in RF front ends. In this paper, we present a low-voltage LNA-mixer pair design based on the common-gate topology. Current-reuse, current bleeding, and charge injection techniques are utilized in order to maximize the gain with minimal additive power consumption. Leveraging our analytical models, the design space can be explored to optimally design the LNA-mixer pair for customizable operating frequency. Simulation results demonstrate the performance improvement using our design technique.

Theoretical analysis of the characteristic impedance in metal–insulator–metal plasmonic transmission lines

We propose a closed form formulation for the impedance of the metal-insulator-metal (MIM) plasmonic transmission lines by solving the Maxwells equations. We provide approximations for thin and thick insulator layers sandwiched between metallic layers. In the case of very thin dielectric layer, the surface waves on both interfaces are strongly coupled resulting in an almost linear dependence of the impedance of the plasmonic transmission line on the thickness of the insulator layer. On the other hand, for very thick insulator layer, the impedance does not vary with the insulator layer thickness due to the weak-coupling/decoupling of the surface waves on each metal-insulator interface. We demonstrate the effectiveness of our proposed formulation using two test scenarios, namely, almost zero reflection in T-junction and reflection from line discontinuity in the design of Bragg reflectors, where we compare our formulation against previously published results.

Analytical modeling of common-gate low noise amplifiers

The exponential growth of wireless portable device market has been increasing the demand for customizable power- efficient transceivers. In this paper, we present an efficient modeling methodology for common-gate low-noise amplifiers (LNAs). Leveraging our models, we designed LNAs to work for different communication standards, GSM at 900 MHz, Bluetooth at 2.4 GHz, and wireless-LAN at 5.6 GHz. Our methodology achieves about 96.45% average accuracy in predicting different figures of merit (FOM) at the center frequency, while it provides Ave orders of magnitude speedup in the design process compared to simulation-based modeling techniques.