Smart Sensing of Multi-bit Resistive Memory using a Single Reference

Emerging Non-Volatile Memories (NVMs) are increasingly being researched for multi-bit capabilities which can be exploited not only for storage (increased memory density) but also for novel applications like in-memory computing e.g. matrix vector multiplication. Such applications require readout circuits, i.e. Sense Amplifiers (SAs) which convert the resistance of the memory cell to digital data. In this work, we propose such a Sense Amplifier (SA) to distinguish between the four states of a ReRAM cell. Unlike conventional multi-bit sensing schemes which require three references to sense four states, the proposed sensing technique requires only a single voltage reference. The proposed SA uses current comparison to sense the first bit and based on the value of the sensed bit, the crucial currents of the SA are manipulated to sense the second bit. The proposed SA is very energy efficient when compared to the state-of-theart (consuming 82.4 fJ in 130 nm process node) while avoiding the need to generate multiple voltage/current references on-chip. Requiring only 25 transistors and a single V_REF , the proposed SA is one of the most compact SA among others in the state-ofthe- art.