EEPROM device as a reconfigurable analog element for neural networks

Abstract

An investigation into the use of EEPROMs (electrically erasable programmable read-only memories) for analog storage is presented, with special consideration given to the problem of reconfigurable weight storage in neural net implementations. Control of either programming voltage or programming time can be used to program the threshold voltage of industry-standard digital EEPROMs to any analog value. Variations in the programming curves of different devices on the same chip as well as changes in the programming curve of a single device with age suggest the need for feedback in any EEPROM-based analog programming strategy. EEPROM charge retention appears to be very good in the analog range and, to first order, temperature compensation of EEPROMs is no more complicated than that for conventional MOS circuits. A particular analog programming scheme which provides about 8 b of resolution per EEPROM device is presented, and the potential uses of EEPROMs in neural net designs are discussed. >