Sub-W Auto-Calibration Bandgap Voltage Reference With 1 Inaccuracy of 0.12% Within-40 C to 120 C

This article presents an auto-calibration technique for current-based bandgap voltage references (BGRs), based on a digitally-assisted auto-calibration loop for calibration cost reduction. We first present a theoretical study of the process variation induced V-EB and Delta V-EB variations in the BJT, which contribute to residual errors in the reference voltage ( V-REF) and its temperature coefficient (TC) after applying conventional one-point trimming. Based on the study, we further propose an automatic one-point trimming methodology using a current digital-to-analog converter (IDAC), which can simultaneously relax the V-EB and Delta V-EB variations, resulting in a small drift in both V-REF and its TC after calibration. Fabricated in 65 nm standard CMOS, the proposed auto-calibrated BGR achieves a measured TC of 22.3 ppm/degrees C at 1.2 V supply within -40 degrees C to 120 degrees C. The line regulation is 1.26 mV/V or 0.13%/V from 1.2 to 2.5 V. Based on ten-chip measurement results, the achieved s/ mu variation in VREF improves from +/- 0.53% to +/- 0.12% within the entire temperature spectrum after applying the proposed auto-calibration technique at 27 degrees C.