Problem in detecting sine signal with arduino due in simulink in external mode s

I am using arduino due and at the analog input I am applying the output of voltage sensor. And in simulink I have taken analog input pin and i am checking signal on scope. But instead of sine I am getting distorted signal which is no where near sine. What should I do to get sine signal. I have tried with sample time 0.00001 and sample time 0 in analog pin still it is showing detecting distorted signal. Is this problem due to external mode?