Minimizing the Jitter of Duty Cycle Distortion Correction Technology Based on Cross Point Eye Diagram Correction

Pattern jitter is a primary contributor to the increase of the bit error rate (BER) in high-speed communications, which occurs in large part due to duty cycle distortion (DCD). By considering DCD caused by transmission links and the distribution of jitter in DCD due to the pattern of the transmission link, this paper proposes a precise control method based on the cross point of the eye diagram to minimize the jitter associated with DCD and to effectively decrease the BER of high-speed digital communications. By capitalizing on the theoretical basis that the main form of DCD is the offset of the cross point of the eye diagram, the technology presented here reconstructs the pattern waveform by using a digital method and incorporates a time variable to precisely control the data edge position during the reconstruction process, thereby stabilizing the cross point at 50% to correct its drift. Accordingly, after fanning out the original pattern buffer and then passing two controllable delay lines with different delays through the buffer in a process that is driven by digital logic operation, the cross point of the waveform is reconstructed by changing the relative time delay of the two signals. As a result, the change in the position of the cross point of the eye diagram is transformed into the precise control of the relative time delay, minimizing the DCD jitter. The theoretical model is verified by experiments, indicating that this method can control the cross point of the non-return-to-zero (NRZ) pattern in the range of 30% to 70% under 3 Gbps with a resolution as great as 1%. Furthermore, this approach can solve the problem of cross point drift of the eye diagram and can significantly decrease the BER caused by DCD jitter.