Yuzo Hirai Kuninori Nishizawa Hardware Implementation of a PCA Learning Network by an Asynchronous PDM Digital Circuit. 65-70 2000 IJCNN (2) http://csdl.computer.org/comp/proceedings/ijcnn/2000/0619/02/06192065abs.htm db/conf/ijcnn/ijcnn2000-2.html#HiraiN00