A slope analog-to-digital converter (ADC) amenable to be fully implemented on a digital field programmable gate array (FPGA) without requiring any external active or passive components is proposed in this paper. The amplitude information, encoded in the transition times of a standard LVDS differential input-driven by the analog input and by the reference slope generated by an FPGA output buffer-is retrieved by an FPGA time-to-digital converter. Along with the ADC, a new online calibration algorithm is developed to mitigate the influence of process, voltage, and temperature variations on its performance. Measurements on an ADC prototype reveal an analog input range from 0.3 V to 1.5 V, a least significant bit (LSB) of 2.6 mV, and an effective number of bits (ENOB) of 7.4-bit at 600 MS/s. The differential nonlinearity (DNL) is in the range between -0.78 and 0.70 LSB, and the integral nonlinearity (INL) is in the range from -0.72 to 0.78 LSB.
Keywords: FPGA; analog-to-digital converter (ADC); differential nonlinearity (DNL); effective number of bits (ENOB); integral nonlinearity (INL); time-to-digital converter (TDC).