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In this paper, a 65nm 1.2V 7-bit 1GSPS A/D converter with a self-calibration technique is proposed. The A/D converter is based on a folding-interpolation structure whose folding rate is 2, interpolation rate is 8. An offset self-calibration circuit with a feedback loop and a recursive digital code inspection is described. The offset self-calibration circuit reduces the variation of the offset voltage, due to process mismatches, parasitic resistors, and parasitic capacitances. The chip has been fabricated with a 65nm 1-poly 6-metal CMOS technology. The effective chip area is 0.87mm2 and the power consumption is about 110mW at 1.2V power supply. The measured SNDR is about 38.48dB when the input frequency is 250MHz at 1GHz sampling frequency. The measured SNDR is 3dB higher than the same ADC without any calibration.