Analysis of DPD signal offset caused by optical asymmetry

A simple model to clearly show the causes of offset in DPD (Differential Phase Detection) signal is suggested. From this model, we can see the offset mechanism in case lens shift and disc tilt occur, respectively. We also suggest the feasibility of using 2-segment DPD. Comparison of 2-seg. DPD with conventional 4-seg. DPD is made.