If the offset is equal to the peak value of the input, the negative peak will rise up to zero volts and the diode will never turn on (meaning that it will not load the input and change the wave shape)...If the offset is equal to the peak value of the input, the negative peak will rise up to zero volts and the diode will never turn on (meaning that it will not load the input and change the wave shape). At this point, the capacitor has a voltage across it that is equivalent to the negative peak value of the input signal and it will behave just like the fixed DC voltage source in the prototype.
