Low current applications, like neuromorphic circuits, where operating currents can be as low as a few nanoamperes or less, suffer from huge transistor mismatches, resulting in around or less than 1-bit precisions. Recently, a neuromorphic programmable-\udkernel 2-D convolution chip has been reported where each pixel included two compact calibrated digital-to-analog\udconverters (DACs) of 5-bit resolution, for currents down to picoamperes. Those DACs were based on MOS ladder structures,\udwhich although compact require unit transistors ( is\udthe number of calibration bits). Here, we present a new calibration\udapproach not based on ladders, but on individually calibratable\udcurrent sources made with MOS transistors of digitally adjustable\udlength, which require only -sized transistors. The scheme includes\uda translinear circuit-based tuning scheme, which allows\udus to expand the operating range of the calibrated circuits with\udgraceful precision degradation, over four decades of operating\udcurrents. Experimental results are provided for 5-bit resolution\udDACs operating at 20 nA using two different translinear tuning\udschemes. Maximum measured precision is 5.05 and 7.15 b, respectively,\udfor the two DAC schemes.
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