AND8T SRAM Macro with Improved Linearity for Multi-bit In-Memory Computing

In this work, we propose a multi-bit precision (4b input, 4b weight and 4b output) in-memory computing (IMC) architecture, based on the voltage scaling and charge sharing scheme, for the artificial intelligence (AI) edge devices. To achieve the efficient computation, a new AND logic based 8T SRAM cell (AND8T) has been used which employs the charge-domain based computation. For such computation, AND8T incorporates an overlaying metal-oxide-metal capacitor (MOM cap) with no bit-cell area overhead. The proposed cell mitigates the linearity issue of multiply and accumulate (MAC) operation for the IMC unit which is highly desirable for the reliable operation of complex neural networks (CNN). Moreover, our high precision AND8T based IMC architecture allows 128 parallel MAC operations avoiding the need of serial multi-bits input implementation through multiple cycles. The proposed design has been successfully verified by the monte carlo simulation results while working at 50MHz clock frequency and 1V supply using standard 65nm node.