Approximate multipliers attract a large interest in the scientific literature that proposes several circuits built with approximate 4-2 compressors. Due to the large number of proposed solutions, the designer who wishes to use an approximate 4-2 compressor is faced with the problem of selecting the right topology. In this paper, we present a comprehensive survey and comparison of approximate 4-2 compressors previously proposed in literature. We present also a novel approximate compressor, so that a total of twelve different approximate 4-2 compressors are analyzed. The investigated circuits are employed to design $8\times 8$ and $16\times 16$ multipliers, implemented in 28nm CMOS technology. For each operand size we analyze two multiplier configurations, with different levels of approximations, both signed and unsigned. Our study highlights that there is no unique winning approximate compressor topology since the best solution depends on the required precision, on the signedness of the multiplier and on the considered error metric.

中文翻译：

---

低功耗近似乘法器的近似4-2压缩器的比较和扩展

近似乘法器在科学文献中引起了极大的兴趣，这些文献提出了用大约 4-2 个压缩机构建的几个电路。由于提议的解决方案数量众多，希望使用近似 4-2 压缩机的设计人员面临着选择正确拓扑的问题。在本文中，我们对先前在文献中提出的大约 4-2 台压缩机进行了全面调查和比较。我们还提出了一种新颖的近似压缩机，以便分析总共十二种不同的近似 4-2 压缩机。所研究的电路用于设计 $8\乘以8$ 和 $16\乘以16$ 乘法器，采用 28nm CMOS 技术实现。对于每个操作数大小，我们分析两个乘法器配置，具有不同级别的近似值，有符号和无符号。我们的研究强调，没有唯一获胜的近似压缩器拓扑结构，因为最佳解决方案取决于所需的精度、乘法器的符号和所考虑的误差度量。