Harmonic distortion correction for 8-bit delay line ADC using gray code

Abstract

Harmonic distortion correction (HDC) is an effective digital calibration technique to estimate and correct errors and distortions in an analog circuit. However, the convergence time is still a concern. In this paper, we propose the injection of a periodic 3-bit gray code sequence for HDC to digitally calibrate an 8-bit delay line ADC. In our simulation results, digital calibration with the gray code injection improves SNDR and SFDR to 42.5 dB and 45.4 dB, respectively, compared with the original SNDR of 25.6 dB and the original SFDR of 25.7 dB, with a 13.5 milliseconds calibration time, which is 64X faster than with injection of pseudorandom numbers (860 milliseconds). Also the SNDR converges to 41.6 dB after averaging 224 samples, while the SNDR with injection of pseudorandom numbers converges to 41.5 dB after 237 samples.