This paper presents FIR digital filters based on stochastic/binary hybrid computation with reduced hardware complexity and high computational accuracy. Recently, some attempts have been made to apply stochastic computation to realization of digital filters. Such realization methods lead to significant reduction of hardware complexity over the conventional filter realizations based on binary computation. However, the stochastic digital filters suffer from lower computational accuracy than the digital filters based on binary computation because of the random error fluctuations that are generated in stochastic bit streams, stochastic multipliers, and stochastic adders. This becomes a serious problem in the case of FIR filter realizations compared with the IIR counterparts because FIR filters usually require larger number of multiplications and additions than IIR filters. To improve the computational accuracy, this paper presents a stochastic/binary hybrid realization, where multipliers are realized using stochastic computation but adders are realized using binary computation. In addition, a coefficient-scaling technique is proposed to further improve the computational accuracy of stochastic FIR filters. Furthermore, the transposed structure is applied to the FIR filter realization, leading to reduction of hardware complexity. Evaluation results demonstrate that our method achieves at most 40dB improvement in minimum stopband attenuation compared with the conventional pure stochastic design.

FDTD (Finite-Difference Time-Domain) method has been widely used for the analysis of photonic devices consisting of sub-wavelength structures. In recent years, increasing efforts have been made to implement the FDTD on GPGPUs (General-Purpose Graphic Processing Units), to shorten simulation time. On the other hand, it is widely recognized that most of the middle- and low-end GPGPUs have difference of computational performance, between single-precision and double-precision type arithmetics. Therefore the type selection of single/double precision for electromagnetic field variables in FDTD becomes a key issue from the viewpoint of the total simulation performance. In this study we investigated the difference of results between the use of single-precision and double-precision. As a most fundamental sub-wavelength photonic structure, we focused on an alternating multilayer (one dimensional periodic structure). Obtained results indicate that significant difference appears for the amplitudes of higher order spatial harmonic waves.

Electromagnetic scattering problems of canonical 2D structures can be analyzed with a high degree of accuracy by using the point matching method with mode expansion. In this paper, we will extend our previous method to 3D electromagnetic scattering problems and investigate the radar cross section of spherical shells and the computational accuracy.