Micro Sensors
Abolfazl Bijari; Sara Nooki
Abstract
Background and Objectives: Accurate measurement of moisture content (MC) in wheat grains is vital for quality control and storage management. This study presents the development of a differential microwave sensor with enhanced sensitivity for detecting MC in wheat grains, leveraging resonant techniques ...
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Background and Objectives: Accurate measurement of moisture content (MC) in wheat grains is vital for quality control and storage management. This study presents the development of a differential microwave sensor with enhanced sensitivity for detecting MC in wheat grains, leveraging resonant techniques to improve detection precision.Methods: The proposed sensor utilizes two identical half-wavelength (λ/2) microstrip resonators symmetrically coupled to a standard 50Ω transmission line. One resonator serves as a reference with a relative permittivity (έr) of 1, while the second is exposed to the sample under test (SUT), where έr > 1. This differential structure enables the identification of dielectric property changes due to moisture variation. The operating principles are theoretically analyzed using even- and odd-mode techniques.Results: The proposed sensor exhibits three distinct transmission zeros (TZs) within the 0.1–2 GHz frequency range, which arise from the harmonic behavior of the resonators. A prototype was fabricated on a low-cost, compact substrate with dimensions of 6 × 4.5 × 0.16 cm³ and was experimentally tested, confirming the simulation results. The sensor demonstrates a high normalized sensitivity of 7.63%.Conclusion: The developed differential microwave sensor demonstrates strong potential for precise and reliable MC detection in wheat grains. Its compact design, cost-effectiveness, and high sensitivity make it a suitable candidate for practical agricultural and food monitoring applications.
Analogue Integrated Circuits
A. Bijari; M. A. Mallaki
Abstract
Background and Objectives: In wireless communications, receivers play an essential role. Among receiver architectures, the direct-conversion receiver (DCR) architecture has been selected due to its high level of integration and low cost. However, it suffers from DC offset due to self-mixing, I/Q imbalance, ...
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Background and Objectives: In wireless communications, receivers play an essential role. Among receiver architectures, the direct-conversion receiver (DCR) architecture has been selected due to its high level of integration and low cost. However, it suffers from DC offset due to self-mixing, I/Q imbalance, and flicker noise.Methods: This paper presents a new LNA-mixer with variable conversion gain (VG-LM) for wireless local area network (WLAN) applications. A low noise transconductance amplifier (LNTA) is used as the transconductance stage in the Gilbert cell mixer. The wide variable conversion gain range is achieved by the change in LNTA’s transconductance and transconductance of the mixer switching transistors.Results: The proposed LNA-mixer is designed and simulated using 0.18µm CMOS technology in Cadence Spectre RF. The post-layout simulations exhibit the proposed circuit operates at 2.4 GHz with a bandwidth of 10 MHz. In addition, the conversion gain is changed from -3.9 dB to 23.9 dB with the variation of the controlled DC voltage from 0.5 to 1.8. At the high gain, the double-sideband noise figure (DSB-NF) is less than 3.7 dB, and its third-order intermodulation point (IIP3) is -9 dBm. The power consumption is 22 mW from the supply voltage of 1.8 V. The circuit occupies 743 µm×775 µm of core chip area.Conclusion: Using the proposed circuit, the RF front end receiver does not need the low noise amplifier (LNA) and variable gain amplifier (VGA).
Analogue Integrated Circuits
F. Shakibaee; A. Bijari; S.H. Zahiri
Abstract
Background and Objectives: Comparators play a critical role in the analog to digital converters (ADCs) and digital to analog converters (DACs). So, different structures have been proposed to improve their performance. Power, delay, offset, and noise are the important factors that have significantly affect ...
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Background and Objectives: Comparators play a critical role in the analog to digital converters (ADCs) and digital to analog converters (DACs). So, different structures have been proposed to improve their performance. Power, delay, offset, and noise are the important factors that have significantly affect the comparator’s performance. In low power applications, power consumption and delay are the critical concerns that should be minimized to obtain better performance. In this work, a low-power and high-speed comparator has been proposed, which is suitable for applications operating at a low power supply.Methods: Based on the conventional structure of the comparator, some modifications are implemented to achieve better performance in terms of power consumption and delay. Additionally, the proposed structure gives great performance when the difference of inputs is very small. To verify the proposed structure, it is designed and simulated in a 0.18 μm CMOS technology with a power supply of 1 V and sampling frequency of 2 MHz.Results: To draw a fair comparison, the conventional and proposed structure is simulated in equal circumstance. The size of transistors is designed with appropriate W/L ratios to achieve appropriate performance. The proposed structure not only reduces the power consumption by 44%, but also it decreases the delay by 9.1%. The power consumption of the proposed structure is around 0.12 µw. The total occupied area by the proposed structure is approximately 127.44 µm2.Conclusion: In this paper, we presented a delay analysis for the proposed dynamic comparator. Also, based on theoretical analyses, a new dynamic comparator consumes less power and operates faster compared with the conventional structure. The simulation results verify the theoretical analysis.
R. Salmani; A. Bijari; S. H. Zahiri
Abstract
Background and Objectives: Due to the rapid development in wireless communications, bandpass filters have become key components in modern communication systems. Among the microwave filter technologies, planar structures of microstrip line are chosen, due to low profile, weight, ease of fabrication, and ...
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Background and Objectives: Due to the rapid development in wireless communications, bandpass filters have become key components in modern communication systems. Among the microwave filter technologies, planar structures of microstrip line are chosen, due to low profile, weight, ease of fabrication, and manufacturing cost.Methods: This paper designs and simulates a new microstrip dual-band bandpass filter. In the proposed structure, three coupled lines and a loaded asymmetric two coupled line are used. The design method is based on introducing and generating the transmission zeros in the frequency response of a wideband single-band filter. A wideband frequency response is obtained using the three coupled lines, and the transmission zeros are achieved using the novel loaded asymmetric two coupled lines.Results: The proposed dual-band filter is designed and simulated on a Rogers RO3210 substrate for WLAN applications. Dimension of the proposed filter is 11.22 mm × 13.04 mm. The electromagnetic (EM) simulation is carried out by Momentum EM (ADS) software. Simulation results show that the proposed dual-band bandpass filter has two pass-bands at 2.4 GHz and 5.15 GHz with a loss of less than 1 dB for two pass-bands.Conclusion: Among the advantages of this filter, low loss, small size, and high attenuation between the two pass-bands can be mentioned.
