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How to force D event to open Z window

Question asked by bandudej.kamorn on Jul 19, 2012
Refer to AN1130 on page 15, 
"If the motor speed is suddenly increased by the user so the Z event will happen earlier. If BEMF signal is already be positive when the phase extremity becomes a floating point thus the signal will not cross the threshold voltage and the ST72141 will not detect the End of demagnetisation event. As a consequence, the ST72141won’t open the Z event detection window. We force an End of demagnetisation event and so the Z window detection is opened in all cases."

Can someone please explain how to detect Z event before End of D is not finish yet? and how/when we can force D event in this case?

Do you have timing diagram of phase current and phase voltage similarly to figure 9. in case of Z event is happen early.