Xmega for high-voltage ADC and processing

Hi all,

I am trying to use Xmega microcontroller's ADC to read and process signal for my project. The project is as follow

The input signal is a 1kV-4kV DC superimposed by a small AC sine signal (can be a couple of volts, maybe on the order of 100Hz).

I need to extract the AC component of the mixed AC-DC signal and obtain it's magnitude and phase (relative phase shift compared to the input AC).

I have a following questions hope you can help me with:

1. Is voltage divider to lower the input voltage range to a rated input voltage range of the Xmega possible? (Obviously I need to be very careful with this large voltage input).

2. Is it possible to implement the digital signal processing algorithm to the code to extract the AC component?

3. If 2 is not a solution, can I design a simple circuit (high-pass filter?) to achieve this task?

4. What Xmega would you recommend for this task?

Thanks