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 $V_{\mathrm{EB}}$ and $\Delta V_{\text {EB}}$ variations in the BJT, which contribute to residual errors in the reference voltage ( $V_{\mathrm{REF}}$ ) 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 $A{V}$ EBand $\Delta V_{\mathrm{EB}}$ variations, resulting in a small drift in both $V_{\mathrm{REF}}$ and its TC after calibration. Fabricated in 65 nm standard CMOS, the proposed auto-calibrated BGR achieves a measured TC of 22.3 ppm/°C at 1.2 V supply within −40 °C to 120 °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 $\sigma /\mu$ variation in $V_{\mathrm{REF}}$ improves from ±0.53% to ±0.12% within the entire temperature spectrum after applying the proposed auto-calibration technique at 27 °C.