High resolution TDC and high linearity DTC for all-digital spur calibration

This paper presents an all-digital spur calibration method based on a high resolution time-to-digital converter (TDC) and high linearity digital-to-time converters (DTC). The proposed TDC achieves high resolution with small area while the high linearity DTCs reduce the calibration time. The timing errors are measured with a Vernier TDC which can amplify the errors to improve the time resolution. The errors will be corrected by DTCs later. By using the proposed TDC, the resolution achieves 200 fs with a total conversion range of ±4.2 ps. The proposed DTCs are based on constant slope charging method driven by two digital-to-analog converters (dAC). Rising and falling edge delay can be controlled independently. With 8-bit DACs and 9 ps linear range for each edge, the maxim integral nonlinearity (iNl) is 41.6 fs. After calibration, time error of each multi-phase signal will be reduced to less than 120 fs on average.