Energy-Efficient Approximate Bus Encoder for I2 C in an Industrial Photoplethysmography Smart Sensor

In ultra-low-power wearable sensors, serial buses such as $\mathbf{I}^{\mathbf{2}} \mathbf{C}$ significantly impact the total energy budget. Approximate bus encoding has emerged as a key strategy for energy-efficient data transmission. While ACME, a state-of-the-art encoding method, has proven effective, it lacks $\mathbf{I}^{\mathbf{2}} \mathbf{C}$ compatibility. This work presents the first fully integrated ACME encoder into the $\mathbf{I}^{\mathbf{2}} \mathbf{C}$ interface of a novel PPG sensor prototype, redesigning it for compatibility and filling the gap from an industrial perspective by providing accurate power evaluations that reflect realistic application scenarios. The results demonstrate that transmission energy and system energy savings reach 33.4% and 8.16%, respectively, with negligible error and overhead.