Minimum energy point tracking for sub-threshold digital CMOS circuits using an in-situ energy sensor

The design of an energy sensor and a minimum energy point tracking algorithm are presented. When synthesized with standard cells in a 0.13μm CMOS process, the tracking algorithm requires 2021 gates (0.008mm²), which consume 32μW when clocked at 100MHz. The proposed energy sensor operates by integrating the voltage drop across a power gating device. A digitally-assisted integrator ensures a wide dynamic range. When operated from a 1.2V supply, the sensor dissipates only 80μW, which is further reduced by a comparator-sharing scheme. The sensor has a resolution of 10fJ and can resolve 0.0025 activity changes in a 0.7MHz bandwidth.