Compact calibration circuit for large neuromorphic arrays

Low current applications, like neuromorphic circuits, where operating currents can be as low as few nano amps or less, suffer from huge transistor mismatches, resulting in around or less than 1-bit precision. Here we present a new calibration approach based on individually calibrated current sources made with MOS transistors of digitally adjustable length, which require only N unit transistors. The scheme includes a translinear circuit based tuning scheme, which allows to expand the operating range of the calibrated circuits with graceful precision degradation, over 4 decades of operating currents. Experimental results are provided for 5-bit resolution DACs operating at 20 nA.