Why are some people always negative?

Hi ,

I am finding it difficult to handle negative people. It is ok if the person who is negative is a friend or colleague but here it is my father. I love my father a lot but these days talking to him really drains me off. He keeps talking all negative things and this really makes me irritated. There is nothing which comes positive from him. Every tiime he sees me he says something negative. How to handle it.? some course of some way of bringing positive change.. please advice.