Showing 6 results for Linearity
A. Bijari, S. H. Keshmiri , W. Wanburee,
Volume 8, Issue 1 (3-2012)
Abstract
This paper presents a nonlinear analytical model for micromechanical silicon ring resonators with bulk-mode vibrations. A distributed element model has been developed to describe the dynamic behavior of the micromechanical ring resonator. This model shows the nonlinear effects in a silicon ring resonator focusing on the effect of large amplitudes around the resonance frequency, material and electrical nonlinearities. Through the combination of geometrical and material nonlinearities, closed-form expressions for third-order nonlinearity in mechanical stiffness of bulk-mode ring resonators are obtained. Using the perturbation method and the method of harmonic balance, the expressions for describing the effect of nonlinearities on the resonance frequency and stability are derived. The results, which show the effect of varying the AC drive voltage, initial gap, DC applied voltage and the quality factor on the frequency response and resonant frequencies, are discussed in detail. The nonlinear model introduces an appropriate method in the field of bulk-mode ring resonator design for achieving sufficient power handling and low motional resistance.
S. Ghavami, B. Abolhassani,
Volume 9, Issue 1 (3-2013)
Abstract
In the down link scenario of code division multiple access (CDMA) systems, multi user detectors (MUDs) such as linear de-correlating detector (LDDs) provide satisfactory symbol error rates (SERs) at the expense of much increased complexity, they require all active users’ spreading sequences, which is impractical from privacy point of view. To overcome this impracticality, a simple matched filter receiver is considered in this paper, which requires no knowledge of co-users’ spreading sequences. However, this simple receiver degrades the SER due to multiple access interference (MAI). To overcome this SER degradation, a zero force (ZF) pre-coder is employed in the transmitter traditionally. Moreover, a composite of CDMA signals has a large peak to average power ratio (PAPR), which causes nonlinear distortion (NLD) at the output of the base station high power amplifier (HPA). This also results in degrading the SER. We analyze the down link scenario of CDMA system to derive an equation for the SER of system with ZF-pre-coder plus HPA in the transmitter and matched filter in the receiver over two cases: additive white Gaussian noise (AWGN) and AWGN plus flat fading channels. Theoretical analysis and numerical results show that the ZF pre-coder increases the total degradation of the link significantly compared with that of the LDD. So, as a solution, rather than using ZF pre-coder, we propose a new method which is called extended joint channel estimation method, it is based on joint estimation of channel gains and LDD operator by the mobile station (MS). In that base station (BS) transmits the row k of LDD operator to the MS k. Simulation results show that the SER of this new proposed method is matched to that of LDD in AWGN channel when the number of pilot symbol repetition is equal to 8. Moreover, this method has the two added advantages of no need for providing the spreading sequences of all co-users and meeting a satisfactory total degradation. Furthermore, our analysis shows that loss in spectral efficiency due to transmitting the pilot symbols in the proposed method is negligible for the practical values of traffic variations.
A. Daghighi,
Volume 9, Issue 3 (9-2013)
Abstract
In this article, a novel concept is introduced to improve the radio frequency (RF) linearity of partially-depleted (PD) silicon-on-insulator (SOI) MOSFET circuits. The transition due to the non-zero body resistance (RBody) in output conductance of PD SOI devices leads to linearity degradation. A relation for RBody is defined to eliminate the transition and a method to obtain transition-free circuit is shown. 3-D Simulations of various body-contacted devices are carried out to extract the transition-free body resistances. To identify the output conductance transition-free concept and its application to RF circuits, a 2.4 GHz low noise amplifier (LNA) is analyzed. Mixed mode device-circuit analysis is carried out to simultaneously solve device transport equations and circuit spice models. FFT calculations are performed on the output signal to compute harmonic distortion figures. Comparing the conventional body-contacted and transition-free SOI LNAs, third harmonic distortion (HD3) and total harmonic distortion (THD) are improved by 16% and 24%, respectively.
Two-tone test is used to analyze third order intermodulation distortions. OIP3 is improved in transition-free SOI LNA by 17% comparing with the conventional body-contacted SOI LNA. These results show the possibility of application of transition-free design concept to improve linearity of RF SOI MOSFET circuits.
A. Afrush, M. Shahriari-Kahkeshi,
Volume 15, Issue 2 (6-2019)
Abstract
This paper proposes an adaptive approximation-based controller for uncertain strict-feedback nonlinear systems with unknown dead-zone nonlinearity. Dead-zone constraint is represented as a combination of a linear system with a disturbance-like term. This work invokes neural networks (NNs) as a linear-in-parameter approximator to model uncertain nonlinear functions that appear in virtual and actual control laws. Minimal learning parameter (MLP) algorithm is proposed to decrease the computational load, the number of adjustable parameters, and to avoid the “explosion of learning parameters” problem. An adaptive TSK-type fuzzy system is proposed to estimate the disturbance-like term in the dead-zone description which further will be used to compensate the effect of the dead-zone, and it does not require the availability of the dead-zone input. Then, the proposed method based on the dynamic surface control (DSC) method is designed which avoids the “explosion of complexity” problem. Proposed scheme deals with dead-zone nonlinearity and uncertain dynamics without requiring the availability of any knowledge about them, and it develops a control input without singularity concern. Stability analysis shows that all the signals of the closed-loop system are semi-globally uniformly ultimately bounded and the tracking error converges to the vicinity of the origin. Simulation and comparison results verify the acceptable performance of the presented controller.
B. Dorostkar Yaghouti,
Volume 19, Issue 2 (6-2023)
Abstract
By increasing the transceiver devices within the 3.1 to 10.6 GHz frequency band, the interferers and strong blockers from different equipment degraded the main received signals, so linearity performance becomes more notable. In this paper, a two-path low noise amplifier (LNA) is proposed for satisfying the overall efficiency of the Ultra-wideband (UWB) radar used in vital sign detection, precise indoor localization, and high data rate wireless communications. A novel high linear circuit is recommended based on Complementary Derivative Superposition (CDS) and Post Distortion (PD) techniques. High pass filter and inductive source degeneration structured input impedance matching. Post layout results of the designed UWB-LNA in 180-nm CMOS represented the average of third-order Intercept Point (IIP3) is 8.1 dBm, S21 is 11 dB and, S11 is below -10 dB. The minimum noise figure (NF) is 3.11 dB. The circuit draws 12.7 mA at 1.4-V. The chip area is 930 µm × 1090 µm. The proposed design in this work exhibits higher FOM compared to similar LNAs, It is clear, high-linearity performance in total bandwidth is an advantage compared to recent articles.
Fatemeh Zare-Mirakabad, Mohammad Hosein Kazemi, Aref Doroudi,
Volume 19, Issue 3 (9-2023)
Abstract
This paper proposes a robust H ∞ -LMI-based primary controller using the Linear Parameter Varying (LPV) modeling for an AC islanded Micro-Grid (IMG). The proposed controller can regulate the frequency and voltage of the IMG under various scenarios, such as load changes, faults, and reconfigurations. Unlike most previous studies that neglected the nonlinearity and uncertainty of the system, this paper represents the system dynamics as a polytopic LPV model in the novel primary control structure. The proposed method computes a state-feedback control by solving the corresponding Linear Matrix Inequalities (LMIs) based on H ∞ performance and stability criteria. The robust primary control is applied to a test IMG in the SIM-POWER environment of MATLAB and evaluated under different scenarios. The simulation results demonstrate the effectiveness and efficiency of the proposed method in maintaining the stability of the frequency and voltage of the IMG.
