Mahmoud Mohammad-Taheri

Guided Mode Resonance Sensor With Enhanced Surface Sensitivity Using Coupled Cross-Stacked Gratings

Cross-stacked gratings are introduced for refractive index sensing based on guided mode resonance (GMR) effect. Reflection from and transmission through cross-stacked gratings is computed after converting the diffraction problem into an equivalent transmission line formulation. This formulation, which lends itself for the analysis of a biperiodic dielectric structure, can be used to calculate diffraction characteristics of the cross-stacked gratings with a high degree of accuracy. With the help of this analysis, it is shown that the cross-stacked gratings possess two mutually coupled GMRs. The method of analysis is then applied to various cross-stacked gratings to estimate their performance when used as a biosensor. It will be shown that, in comparison with conventional single grating GMR sensor with equal available area, a roughly two-fold surface sensitivity, equal bulk sensitivity, and extremely narrow resonance linewidth can be obtained by using cross-stacked gratings. Consequently, this structure improves detection ability of the GMR biosensor particularly for small analyte detection.

A 59–66 GHz Highly Stable Millimeter Wave Amplifier in 130 nm CMOS Technology

The design and fabrication of four-stage cascaded mm-wave low noise amplifiers (LNAs) in a 130 nm CMOS technology are presented. The simultaneous high stability factor and low noise figure are obtained using proper inductors in both gate and source of the transistor. Measured gain of 14.7 dB with a 7 GHz bandwidth has been achieved. The larger inductors are realized with microstrip lines to improve the performance of the LNA and minimize the circuit size.

WAVE ANALYSIS FOR INDUCTIVELY MATCHED MILLIMETER WAVE AMPLIFIER DESIGN

A new design approach based on wave analysis has been implemented in order to derive voltage gain, center frequency and bandwidth of millimeter wave amplifler using parameters of transmission lines (TL). The derived formula allow one to design high frequency amplifler with predetermined bandwidth and centner frequency. It has been shown that in the case of lossy TL or at high frequency, circuit theory cannot predict the amplifler gain behavior while presented wave theory can accurately predict the frequency response of the amplifler in both low and high frequency ranges.

A compact wideband differential interconnect for complete series DC-isolation of integrated circuits above 100 GHz

A wideband interconnect with complete DC-isolation property (both in the Signal and Ground paths) for differential TEM transmission lines (like broadside-coupled striplines) is presented. The overall length of the proposed structure is only 0.1λg at the center frequency of 100 ∼ 500 GHz frequency band. The simulated interconnect shows more than 20 dB of return losses at the input and output ports in 130 ∼ 280 GHz band (about 0.7 octave). In addition, more than 15dB of return losses is achieved in the simulations in the entire 100 ∼ 500 GHz frequency band. The built-in DC-isolation property of both the Signal and Ground paths, makes the presented interconnect a suitable solution for Signal-Ground swapping applications of integrated active circuits, like that of the microstrip to inverted-microstrip transitions. The presented design procedure is applicable to various standard IC fabrication processes.

One-dimensional finite-elements method for the analysis of whispering gallery microresonators

By taking advantage of axial symmetry of the planar whispering gallery microresonators, the three-dimensional (3D) problem of the resonator is reduced to a two-dimensional (2D) one; thus, only the cross section of the resonator needs to be analyzed. Then, the proposed formulation, which works based on a combination of the finite-elements method (FEM) and Fourier expansion of the fields, can be applied to the 2D problem. First, the axial field variation is expressed in terms of a Fourier series. Then, a FEM method is applied to the radial field variation. This formulation yields an eigenvalue problem with sparse matrices and can be solved using a well-known numerical technique. This method takes into account both the radiation loss and the dielectric loss; hence, it works efficiently either for high number or low number modes. Efficiency of the method was investigated by comparison of the results with those of commercial software.

Improvements in the Noise Theory of the MMIC Distributed Amplifiers

Exact and simple expressions have been obtained for the intrinsic noise figure of monolithic microwave integrated circuit distributed amplifiers (DAs). The method has been applied on both MESFET and HBT DAs. It has been shown that the complexity of the obtained formulas is much less than that of the previously published literature. The results of the new theory are then compared with that of the previous theories and it has been shown that the results exactly match.

Computationally efficient algorithm for reducing the complexity of software radio receiver's filter bank

This paper presents a computationally efficient method for extracting individual radio channels from the output of the wideband A/D converter. In a software radio, the extraction of individual channels from the output of the wideband A/D converter is by far the most computationally demanding task; hence it is very important to devise computationally efficient algorithms for this task. In this paper we proposed a new algorithm by assuming the symmetric signal with periods of the length-P (number of coefficients in low pass filter prototype) as an input signal to the subsampled filter bank that is derived from DFT filter bank. Also we divide the complex input x[n] into real and imaginary parts, then we perform operations in each part using two filter bank running in parallel. Finally we add outputs of two parts. With employing this algorithm to the subsampled filter bank channelizer, the complexity of filter bank channelizer was reduced by considerable amount of %81

A 77 GHz controllable gain low noise amplifier

A 77 GHz low noise amplifier has been designed using common source topology implemented in low cost CMOS technology for various applications. A new method has been proposed for the design of the amplifier. In this method, input/output matching networks and transistor gate widths have been optimized for maximum gain and minimum noise figure. The design is flexible such that the LNA can operate in both high gain/high power and low gain/low power modes with low noise figure of less than 7 dB at 77 GHz. Amplifier gain is better than 18 dB consuming 60mW of dc power and it is better than 14.5 dB consuming 30 mW of dc power. The input and output return losses are better than 10 dB in the frequency range of 72 to 82 GHz.

Comparing the Performance of MMIC Matrix and Distributed Amplifiers

A comparison is made between the performance of the MMIC matrix and distributed amplifiers. It has been shown that based on the analytical formulations, in most typical cases a cascaded dual stage distributed amplifier has more gain than that of a two-tier matrix amplifier with the same number of transistors; however the difference is not significant. Results of the analytical approach are then compared with the simulated and the measured results and a good agreement between the results has been obtained. Then other scattering parameters of the matrix and distributed amplifiers have been compared.

Improvements in the Design of Matrix Distributed Amplifiers

A simple method for the gain improvement of matrix distributed amplifiers is presented. The method is based on modifying the central transmission line of the matrix amplifier without any changes in the input and output transmission lines. In the new method the termination impedances in the central transmission line are modified and the transmission line is replaced by an impedance matching circuitry. It has been shown that the new method can significantly improve the gain while preserving the input and output return losses of the amplifier.