Sub-μW Auto-Calibration Bandgap Voltage Reference With 1σ Inaccuracy of ± 0.12% Within − 40°C to 120°C
U Chi-Wa, Man‐Kay Law, Rui P. Martins, Chi‐Seng Lam
Abstract
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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm{EB}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta V_{\text {EB}}$ </tex-math></inline-formula> variations in the BJT, which contribute to residual errors in the reference voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm{REF}}$ </tex-math></inline-formula> ) 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$A{V}$ </tex-math></inline-formula> EBand <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta V_{\mathrm{EB}}$ </tex-math></inline-formula> variations, resulting in a small drift in both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm{REF}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma /\mu $ </tex-math></inline-formula> variation in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm{REF}}$ </tex-math></inline-formula> improves from ±0.53% to ±0.12% within the entire temperature spectrum after applying the proposed auto-calibration technique at 27 °C.