A Temperature and Process Robust Logarithmic Circuit for CIM Application

This paper presents a logarithmic interface circuit for reading current from a CIM (Computing-In-Memory) array. A BJT array is used to generate a logarithmic voltage, which is then compensated for temperature-induced variations in the output current using a cross-linear analog multiplier and a temperature-insensitive reference current generated on-chip. The proposed circuit is implemented in a standard 65 nm CMOS process and occupies an analog core area of 241 μm × 116 μm. Modules that scale with the array size require an additional 3, 000 μm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. Post-layout simulation results show that, under a 1.2 V supply voltage and an input current from 10 μA to 100 μA, the circuit maintains less than 4% variation due to process and temperature fluctuations across a temperature range of 45°C to 95°C. Additionally, at 45°C, the circuit exhibits good dynamic performance for periodic exponential input currents with a frequency of 1 MHz.