Imager with Dynamic LSB Adaptation and Ratiometric Readout for Low-Bit Depth 5-μW Peak Power in Purely-Harvested Systems

An imager with μW peak power is introduced for purely-harvested operation. The LSB is dynamically adapted to the light intensity of the scene for aggressive bit depth downscaling, avoiding traditional dynamic range over-margining across practical light intensities under fixed LSB. Ratiometric readout of pixel current cancels threshold voltage mismatch. A 256×256-pixel 180-nm imager shows 5-μW power at 1 fps and 4 bits, while keeping ImageNet classification accuracy drop to percentage points under 75-dB ambient light range, across original and brightness-adjusted images.