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As many digital signal processing (DSP) applications such as digital filtering are inherently error-tolerant, approximate computing has attracted significant attention. A multiplier is the fundamental component for DSP applications and takes up the most part of the resource utilization, namely power and area. A multiplier consists of partial product arrays (PPAs) and compressors are often used to reduce partial products (PPs) to generate the final product. Approximate computing has been studied as an innovative paradigm for reducing resource utilization for the DSP systems. In this paper, a 4:2 approximate compressor-based multiplier is studied. Approximate 4:2 compressors are designed with a practical design criterion, and an approximate multiplier that uses both truncation and the proposed compressors for PP reduction is subsequently designed. Different levels of truncation and approximate compression combination are studied for accuracy and electrical performance. A practical selection algorithm is then leveraged to identify the optimal combinations for multiplier designs with better performance in terms of both accuracy and electrical performance measurements. Two real case studies are performed, i.e., image processing and a finite impulse response (FIR) filter. The design proposed in this paper has achieved up to 16.96% and 20.81% savings on power and area with an average signal-to-noise ratio (SNR) larger than 25dB for image processing; similarly, with a decrease of 0.3dB in the output SNR, 12.22% and 30.05% savings on power and area have been achieved for an FIR filter compared to conventional multiplier designs.

An experimental investigation has been carried out to know about the performance improvement of a household refrigerator using phase change material (PCM). PCMs are used as latent heat thermal storage system to enhance the heat transfer of the evaporator. PCM is located behind the five sides of the evaporator cabinet in which the evaporator coil is immersed. Water (melting point 0°C) and Eutectic solutions (melting point −5°C) are used as PCMs for this experiment at different thermal loads. Depending on the types of PCM and thermal load, around 20–27% COP improvement of the refrigeration cycle has been observed with PCM with respect to without PCM. With the increase of the quantity of PCM (0.003 to 0.00425 m³) COP increases about 6%. Between two different PCMs the COP improvement for Eutectic solution is higher than Water. The experimental results with PCM confirm that, depending on the thermal load and the types of PCM average compressor running time per cycle is reduced significantly and it is found about 2–36% as compared to without PCM.

Approximate arithmetic circuits have been considered as an innovative circuit paradigm with improved performance for error-resilient applications which could tolerant certain loss of accuracy. In this paper, a novel approximate multiplier with a different scheme of partial product reduction is proposed. An analysis of accuracy (measured by error distance, pass rate and accuracy of amplitude) as well as circuit-based design metrics (power, delay and area, etc.) is utilized to assess the performance of the proposed approximate multiplier. Extensive simulation results show that the proposed design achieves a higher accuracy than the other approximate multipliers from the previous works. Moreover, the proposed design has a better performance under comprehensive comparisons taking both accuracy and circuit-related metrics into considerations. In addition, an error detection and correction (EDC) circuit is used to correct the approximate results to accurate results. Compared with the exact Wallace tree multiplier, the proposed approximate multiplier design with the error detection and correction circuit still has up to 15% and 10% saving for power and delay, respectively.

This paper presents the development of a numerical, iterative and nonisentropic model for the thermodynamic processes of a reciprocating compressor of a refrigeration system operating at steady state. The mathematical model was implemented using the scientific software Engineering Equation Solver (EES) and it is based on the application of the energy equations in four regions of the compressor: inlet duct and chambers of pre-compression, compression, and post-compression. The model was validated with experimental data collected from an open-drive reciprocating compressor, operating with the refrigerant R-134a at different suction and discharge pressures and with different compressor rotational speeds. Model validation was made comparing the values of the mass flow rate and the discharge temperature of the compressor generated by the model with their corresponding experimental values for 33 experimental tests, the mean relative difference was $-$0.2% for the discharge temperature and 2.9% for mass flow rate. In this validation, the output variables of the model were calculated considering the uncertainties from the input variables. The theoretical mean standard uncertainty is 2% for discharge temperature and 6% for mass flow rate. An analysis of the capacitive and thermal performance of the compressor was made using the model, which demonstrates a decrease in the capacitive and thermal efficiencies for increasing the pressure ratio or clearance volume.

With transistors reaching nanometer dimensions, dissipated energy has become of great importance in recent years. A practical approach to reducing energy consumption is to use logic-in-memory (LIM) structures based on magnetic tunnel junction (MTJ) devices combined with approximate computing. In this paper, we propose energy-efficient MTJ/FinFET-based approximate 5:2 compressors for error-resilient in-memory computing, providing an accuracy close to the exact design (1.54% error rate) while reducing the energy consumption by more than 50%. The innovative Boolean equations and the structure of the proposed approximate circuits based on spin-Hall effect assisted MTJs lead to a significantly more effective compromise between energy and accuracy than the previous exact and approximate counterparts. The simulation results provided using HSPICE with 7nm FinFETs and SHE-assisted MTJ models demonstrate the superior hardware parameters of the proposed designs. Furthermore, the MATLAB simulations show an average peak signal-to-noise ratio (PSNR) of more than 43 and an average structural similarity index metric (SSIM) of more than 0.99 across image multiplication, sharpening, and smoothing operations.

In the era of low-power very large-scale integration design, approximate computing is a soaring design paradigm that assures energy-efficient circuit design at the cost of some accuracy. Multiplication is a very important operation of an arithmetic unit and compressor is the inherent part of the multiplier. In this paper, an energy-efficient design of a 4:2 approximate compressor is proposed. The inclusion of the extra leakage control transistors in the logic has led to leakage power reduction, which ultimately reduces the power dissipation in the circuits. The proposed 4:2 compressor is simulated at 10nm fin-field effect transistor (FinFET) technology. The proposed compressor has been verified for its functionality and robustness. The proposed design shows a power dissipation of 154.48nW and a delay of 9.16ps. In comparison to other 4:2 approximate compressors, the proposed compressor shows the least power dissipation, the lowest power delay product (PDP) and the highest robustness. The power dissipation of the proposed compressor is 92.84% less than that of the base compressor. The PDP of the designed compressor is 80.58% less than the minimum PDP among other compressors. The aging analysis for the negative bias temperature instability (NBTI) effect is also checked for the proposed compressor and compared with the existing designs.

In this paper, according to the application practice of scroll compressor for refrigeration and air-conditioning, various factors affecting the whole refrigeration effect of the compressor are studied, the influence of scroll wrap's different forms on compressor exhaust angle and the compression ratio is stated, and it establishes the working principle simulation of the compressor's main parts, and further corrects the form of vortex lines according to simulation results.