NMOS-based gaussian-element-matching analog associative memory

An analog associative memory technology has been developed based on a Gaussian-type element matching circuit aiming at high density integration. The Gausian-like current voltage characteristics of the matching cell is produced by cross-connected four NMOS transistors. It has two floating gates and two complementary analog signals are supplied via capacitance coupling. A compact digital-to-analog converter (DAC) circuit has been developed for on-chip element parallel conversion. A cyclic DAC architecture was employed using a single CMOS-inverter as its gain stage. We have introduced a double reset scheme to the switched-capacitor inverter and significantly improved the buffer characteristics of the CMOS inverter in spite of its finite gain. The circuit ideas have been verified by measurements on experimental chips fabricated in a 0.6-µm double-poly CMOS process.