This paper presents a calibration scheme for reference error caused by signal dependent switching transient in a high speed SAR ADC. The scheme has a little hardware overhead, which is not dependent on the type of the input signal and is able to run in the background without interrupting the ADC's normal operation. The calibration along with the SAR ADC are implemented in a 65 nm CMOS and the measurement results show that the proposed scheme effectively improves the SNDR of an 11b SAR ADC by ∼9 dB. The calibration allows the placement of only 3 pF decoupling capacitance in the reference voltages. The prototype achieves 100 MS/s sampling rate with a total power consumption of 1.6 mW at a 1.2 V supply. Plus, it exhibits a 59.03 dB and 60.4 dB SNDR at Nyquist and low input frequency, respectively, yielding a Walden FoM@Nyquist of 21.9 fJ/conv.-step. The total core area is 0.011 mm which includes the decoupling capacitor.