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Electronics
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Circuits and Systems for Approximate Computing
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Circuits and Systems for Approximate Computing

A special issue of Electronics (ISSN 2079-9292). This special issue belongs to the section "Circuit and Signal Processing".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 26453

Special Issue Editor

Prof. Dr. Sunggu Lee

E-Mail Website
Guest Editor
Department of Electrical Engineering, Pohang University of Science and Technology, 77 Cheongam-ro, Nam-gu, Pohang 37673, Republic of Korea
Interests: low-power circuits for deep learning; approximate computing; parallel computing
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

With the increasing need for power-efficient circuits and systems in mobile applications and extremely computer-intensive or I/O-intensive applications, there has been increased interest in the use of circuits and systems that may possibly sacrifice accuracy and/or performance for low power usage. Referred to as approximate computing, such techniques have been shown to be highly useful for neural network-based artificial intelligence techniques in error resilient applications such as image classification or action recognition, in which an extremely large number of computations are necessary while small losses in accuracy levels can be tolerated and may be barely noticeable. Such approximate computing circuits and systems can also be useful at a more basic level, providing extremely power-efficient low-level modules such as adders, multipliers, logarithm circuits, floating point arithmetic units, etc., that can then be used to build up specialized computer architectures that enable power-efficient neural processing units and other advanced applications. In this Special Issue, papers are sought on all topics related to circuits and systems for approximate computing, including basic arithmetic circuits and entire systems that use approximate computing techniques for low power usage.

Prof. Dr. Sunggu Lee
Guest Editor

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Keywords

  • approximate computing
  • low power
  • computer arithmetic
  • error resilient applications
  • neural network accelerators

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Published Papers (7 papers)

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Research

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17 pages, 4727 KiB  
Article
Improving the Quality Degradation of Dynamically Configurable Approximate Multipliers via Data Correlation
by Fabio Frustaci
Electronics 2021, 10(17), 2063; https://doi.org/10.3390/electronics10172063 - 26 Aug 2021
Viewed by 1936
Abstract
In the last few years, dynamically configurable approximate multipliers have been explored to tune the energy-quality trade-off in error-tolerant applications at runtime. Typically, the multiplier accuracy is adjusted by adding a constant correction factor equal to the multiplier mean error to the result, [...] Read more.
In the last few years, dynamically configurable approximate multipliers have been explored to tune the energy-quality trade-off in error-tolerant applications at runtime. Typically, the multiplier accuracy is adjusted by adding a constant correction factor equal to the multiplier mean error to the result, which is found offline assuming a predetermined input distribution. This paper describes a simple approach to update the correction term at runtime, thus adapting it to the actual incoming inputs. It takes advantage of the spatial and/or temporal correlation typically shown by input data in error-tolerant applications, such as image and video processing. When applied to a typical case study implemented with a commercial UTBB FDSOI 28 nm technology, the proposed approach shows an energy reduction of up to 34% at iso-quality and a quality improvement of up to +9 dB, −4× and +35% at iso-energy, in terms of peak-to-noise ratio (PSNR), normalized error distance (NED) and structural similarity index metric (SSIM) respectively, compared to the traditional technique based on a constant correction factor. Full article
(This article belongs to the Special Issue Circuits and Systems for Approximate Computing)
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13 pages, 1506 KiB  
Article
A High-Accuracy Stochastic FIR Filter with Adaptive Scaling Algorithm and Antithetic Variables Method
by Ying Zhang, Yubin Zhu, Kaining Han, Junchao Wang and Jianhao Hu
Electronics 2021, 10(16), 1937; https://doi.org/10.3390/electronics10161937 - 11 Aug 2021
Cited by 2 | Viewed by 2413
Abstract
Digital filter is an important fundamental component in digital signal processing (DSP) systems. Among the digital filters, the finite impulse response (FIR) filter is one of the most commonly used schemes. As a low-complexity hardware implementation technique, stochastic computing has been applied to [...] Read more.
Digital filter is an important fundamental component in digital signal processing (DSP) systems. Among the digital filters, the finite impulse response (FIR) filter is one of the most commonly used schemes. As a low-complexity hardware implementation technique, stochastic computing has been applied to overcome the huge hardware cost problem of high-order FIR filters. However, the stochastic FIR filter (SFIR) scheme suffers from long processing latency and accuracy degradation. In this paper, the bit stream representation noise is theoretically analyzed, and an adaptive scaling algorithm (ASA) is proposed to improve the accuracy of SFIR with the same bit stream length. Furthermore, a novel antithetic variables method is proposed to further improve the accuracy. According to the simulation results on a 64-tap FIR filter, the ASA and AV methods gain 17 dB and 6 dB on the signal-to-noise ratio (SNR), respectively. The hardware implementation results are also presented in this paper, which illustrates that the proposed ASA-AV-SFIR filter increases 4.6 times hardware efficiency with respect to the existing SFIR schemes. Full article
(This article belongs to the Special Issue Circuits and Systems for Approximate Computing)
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20 pages, 7647 KiB  
Article
Approximate Array Multipliers
by Padmanabhan Balasubramanian, Raunaq Nayar and Douglas L. Maskell
Electronics 2021, 10(5), 630; https://doi.org/10.3390/electronics10050630 - 9 Mar 2021
Cited by 13 | Viewed by 4421 | Correction
Abstract
This article describes the design of approximate array multipliers by making vertical or horizontal cuts in an accurate array multiplier followed by different input and output assignments within the multiplier. We consider a digital image denoising application and show how different combinations of [...] Read more.
This article describes the design of approximate array multipliers by making vertical or horizontal cuts in an accurate array multiplier followed by different input and output assignments within the multiplier. We consider a digital image denoising application and show how different combinations of input and output assignments in an approximate array multiplier affect the quality of the denoised images. We consider the accurate array multiplier and several approximate array multipliers for synthesis. The multipliers were described in Verilog hardware description language and synthesized by Synopsys Design Compiler using a 32/28-nm complementary metal-oxide-semiconductor technology. The results show that compared to the accurate array multiplier, one of the proposed approximate array multipliers viz. PAAM01-V7 achieves a 28% reduction in critical path delay, 75.8% reduction in power, and 64.6% reduction in area while enabling the production of a denoised image that is comparable in quality to the image denoised using the accurate array multiplier. The standard design metrics such as critical path delay, total power dissipation, and area of the accurate and approximate multipliers are given, the error parameters of the approximate array multipliers are provided, and the original image, the noisy image, and the denoised images are also depicted for comparison. Full article
(This article belongs to the Special Issue Circuits and Systems for Approximate Computing)
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11 pages, 450 KiB  
Article
ASAD-RD: Accuracy Scalable Approximate Divider Based on Restoring Division for Energy Efficiency
by Jonghyun Jeong and Youngmin Kim
Electronics 2021, 10(1), 31; https://doi.org/10.3390/electronics10010031 - 28 Dec 2020
Cited by 4 | Viewed by 3050
Abstract
Approximate computing can considerably improve energy efficiency by mitigating the accuracy requirements of calculations in error resilient application programming, such as machine learning, audio–video signal processing, data mining, and search engines. In this study, we propose an approximate divider for dynamic energy-quality scaling, [...] Read more.
Approximate computing can considerably improve energy efficiency by mitigating the accuracy requirements of calculations in error resilient application programming, such as machine learning, audio–video signal processing, data mining, and search engines. In this study, we propose an approximate divider for dynamic energy-quality scaling, which involves a trade-off between accuracy and latency. Previous approximate dividers for dynamic energy-quality scaling are well-configured, but lack energy-quality scalability. The key is to create a more accurate dynamic approximate divider while extending the limits of accuracy to maximize energy efficiency and meet various accuracy requirements. The proposed divider, called the accuracy scalable approximate divider based on restoring division (ASAD-RD), uses restoring division to significantly improve the error of the approximate divider and to use less latency. For the 8-bit division, SAADI, the previous design, has an average accuracy of 90.78% to 98.77%; however, ASAD-RD can improve the accuracy between 95.2% and 99.23% and hardly requires additional power consumption. Furthermore, for the same target accuracy, ASAD-RD requires fewer cycle iterations than SAADI. Thus, ASAD-RD requires lower energy than SAADI and can operate as an energy-efficient approximate divider. Full article
(This article belongs to the Special Issue Circuits and Systems for Approximate Computing)
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13 pages, 3125 KiB  
Article
Approximate LSTM Computing for Energy-Efficient Speech Recognition
by Junseo Jo, Jaeha Kung and Youngjoo Lee
Electronics 2020, 9(12), 2004; https://doi.org/10.3390/electronics9122004 - 25 Nov 2020
Cited by 21 | Viewed by 3419
Abstract
This paper presents an approximate computing method of long short-term memory (LSTM) operations for energy-efficient end-to-end speech recognition. We newly introduce the concept of similarity score, which can measure how much the inputs of two adjacent LSTM cells are similar to each other. [...] Read more.
This paper presents an approximate computing method of long short-term memory (LSTM) operations for energy-efficient end-to-end speech recognition. We newly introduce the concept of similarity score, which can measure how much the inputs of two adjacent LSTM cells are similar to each other. Then, we disable the highly-similar LSTM operations and directly transfer the prior results for reducing the computational costs of speech recognition. The pseudo-LSTM operation is additionally defined for providing the approximate computation with reduced processing resolution, which can further relax the processing overheads without degrading the accuracy. In order to verify the proposed idea, in addition, we design an approximate LSTM accelerator in 65 nm CMOS process. The proposed accelerator newly utilizes a number of approximate processing elements (PEs) to support the proposed skipped-LSTM and pseudo-LSTM operations without degrading the energy efficiency. Moreover, sparsity-aware scheduling is introduced by introducing the small-sized on-chip SRAM buffer. As a result, the proposed work provides an energy-efficient but still accurate speech recognition system, which consumes 2.19 times less energy than the baseline architecture. Full article
(This article belongs to the Special Issue Circuits and Systems for Approximate Computing)
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19 pages, 5448 KiB  
Article
Efficient Approximate Adders for FPGA-Based Data-Paths
by Stefania Perri, Fanny Spagnolo, Fabio Frustaci and Pasquale Corsonello
Electronics 2020, 9(9), 1529; https://doi.org/10.3390/electronics9091529 - 18 Sep 2020
Cited by 16 | Viewed by 5268
Abstract
Approximate computing represents a powerful technique to reduce energy consumption and computational delay in error-resilient applications, such as multimedia processing, machine learning, and many others. In these contexts, designing efficient digital data-paths is a crucial concern. For this reason, the addition operation has [...] Read more.
Approximate computing represents a powerful technique to reduce energy consumption and computational delay in error-resilient applications, such as multimedia processing, machine learning, and many others. In these contexts, designing efficient digital data-paths is a crucial concern. For this reason, the addition operation has received a great deal of attention. However, most of the approximate adders proposed in the literature are oriented to Application Specific Integrated Circuits (ASICs), and their deployment on different devices, such as Field Programmable Gate Arrays (FPGAs), appears to be unfeasible (or at least ineffective). This paper presents a novel approximate addition technique thought to efficiently exploit the configurable resources available within an FPGA device. The proposed approximation strategy sums the k least significant bits two-by-two by using 4-input Look-up-Tables (LUTs), each performing a precise 2-bit addition with the zeroed carry-in. In comparison with several FPGA-based approximate adders in the existing literature, the novel adder achieves markedly improved error characteristics without compromising either the power consumption or the delay. As an example, when implemented within the Artix-7 xc7a100tcsg324-3 chip, the 32-bit adder designed as proposed here with k = 8 performs as fast as its competitors and reduces the Mean Error Distance (MED) by up to 72% over the state-of-the-art approximate adders, with an energy penalty of just 8% in the worst scenario. The integration of the new approximate adder within a more complex application, such as the 2D digital image filtering, has shown even better results. In such a case, the MED is reduced by up to 97% with respect to the FPGA-based counterparts proposed in the literature. Full article
(This article belongs to the Special Issue Circuits and Systems for Approximate Computing)
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Review

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23 pages, 5042 KiB  
Review
Asynchronous Floating-Point Adders and Communication Protocols: A Survey
by Pallavi Srivastava, Edwin Chung and Stepan Ozana
Electronics 2020, 9(10), 1687; https://doi.org/10.3390/electronics9101687 - 15 Oct 2020
Cited by 7 | Viewed by 4607
Abstract
Addition is the key operation in digital systems, and floating-point adder (FPA) is frequently used for real number addition because floating-point representation provides a large dynamic range. Most of the existing FPA designs are synchronous and their activities are coordinated by clock signal(s). [...] Read more.
Addition is the key operation in digital systems, and floating-point adder (FPA) is frequently used for real number addition because floating-point representation provides a large dynamic range. Most of the existing FPA designs are synchronous and their activities are coordinated by clock signal(s). However, technology scaling has imposed several challenges like clock skew, clock distribution, etc., on synchronous design due to presence of clock signal(s). Asynchronous design is an alternate approach to eliminate these challenges imposed by the clock, as it replaces the global clock with handshaking signals and utilizes a communication protocol to indicate the completion of activities. Bundled data and dual-rail coding are the most common communication protocols used in asynchronous design. All existing asynchronous floating-point adder (AFPA) designs utilize dual-rail coding for completion detection, as it allows the circuit to acknowledge as soon as the computation is done; while bundled data and synchronous designs utilizing single-rail encoding will have to wait for the worst-case delay irrespective of the actual completion time. This paper reviews all the existing AFPA designs and examines the effects of the selected communication protocol on its performance. It also discusses the probable outcome of AFPA designed using protocols other than dual-rail coding. Full article
(This article belongs to the Special Issue Circuits and Systems for Approximate Computing)
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