An 11-Bit 10 MS/s SAR ADC with C–R DAC Calibration and Comparator Offset Calibration

Abstract

An 11-bit 10 MS/s successive approximation register (SAR) analog-to-digital converter (ADC) is proposed for low-power and small-area applications. A 10-bit differential capacitor–resistor (C–R) digital-to-analog converter (DAC) is used to minimize the area of a DAC. The use of a C–R DAC reduces the capacitor area of a SAR ADC used CDAC by 75%. A capacitor calibration for the upper 5-bit capacitors of the C–R DAC is proposed to increase the linearity of the C–R DAC. To evaluate the proposed SAR ADC, an 11-bit 10 MS/s SAR ADC is implemented using a 180 nm 1-poly six-metal CMOS process with a supply of 1.8 V. The proposed SAR ADC has an effective number of bits (ENOBs) of 10.3 bits at a sampling rate of 10 MS/s for a 3.6-VPP differential sinusoidal analog input with a frequency of 4.789 MHz. The measured ENOBs is 10.45 bits when the frequency of the analog input signal is 42.39 kHz. The proposed C–R DAC calibration including comparator offset calibration improves the performances of differential nonlinearity (DNL) and integral nonlinearity (INL) from −1/+1.26 LSBs and −1.98/+1.96 LSBs to −0.97/+0.85 LSBs and −0.79/+0.83 LSBs, respectively.