Subthreshold Current Mode Design of Gabortype CNN Image Filters.pdf

Proc. European Conf erence on Circuit Theory and Design, Stresa, Italy, pp. 1163-1166, Aug. 99 Subthreshold Current Mode Design of Gabor-type CNN Image Filters Bertram E. SHI1 Abstract measured results from a 32 pixel 1D prototype which verify the expected operation, as well as an initial com- We have reported CNN implementations of 1D and 2D parison with previous above threshold designs. focal plane architectures for filtering images with odd and even symmetric orientation selective filters similar 2 Current Mode Architecture for Gabor-type to Gabor filters. These implementations used transistor Filtering circuits operating above threshold. While these imple- mentations are fast, they also require a large amount of We distinguish between a voltage versus current mode power. Since many applications may not require circuit by the way in which the signals of interest are extremely fast frame rates, it is reasonable to trade represented. A voltage mode circuit architecture for some of the computing speed for reduced power con- Gabor-type filtering in 1D is shown in Figure 1. sumption. In this paper, we describe a circuit architec- ture for Gabor-type image filtering using transistors G0 operating in subthreshold. We exploit the concept of G G the transistor as a pseudo-conductance or diffuser and vi(m – 1) 1 vi(m) 1 vi(m + 1) use a current, rather than voltage as the primary repre- sentati