Embedded Analog Nonvolatile Memory With Bidirectional and Linear Programmability

Nonvolatile storage of analog values with floating-gate transistors has been useful for many applications. While most proposed analog nonvolatile memory devices employ electron tunneling to modify floating-gate charges, this brief presents an embedded analog nonvolatile memory device that employs only hot-carrier injections to achieve bidirectional programmability. Without using electron tunneling, the proposed circuit not only avoids multiplexing high-voltage signals but also facilitates direct storage of new data. In addition, each memory cell incorporates a simple inverter to make the programming process nearly linear, facilitating bidirectional and linear adaptability for neuromorphic systems. A prototype array of the analog memory has been fabricated with the standard CMOS 0.35- technology. The chip includes a simple on-chip comparator to program the analog memory accurately and automatically by negative feedback. The effective resolution is more than 8 bits over a dynamic range of 1.4 V. The intercell disturbance during programming and the data retention ability are also examined.