Mixed-mode correlator for micropower acoustic transient classification

A mixed-mode very large scale integration (VLSI) processor for acoustic transient classification performs a running correlation between a time-frequency decomposed analog input signal and a corresponding template. Differential encoding of the inputs allows simplification of the multiply-and-accumulate operations, operating on binary templates and positive-valued inputs, implemented in current mode with eight MOS transistors per cell including SRAM template storage. The use of a bucket-brigade device (BED) instead of a charge-coupled device (CCD) for shift-and-accumulate operations allows long integration times necessary for acoustic transients spanning several hundred milliseconds. Correlated double sampling at the output compensates for dark current losses in the BED and other common-mode effects. The 64×16 time-frequency correlator measures 700 μm×1170 μm in a 1.2-μm CMOS process and dissipates an average of 30 μW in continuous operation