Set Current caretposition in viewport Top wpf richtextbox?

Question

I am working in WPF. I want to show current caretposition in viewport top. I already tried the BringIntoView() Method. It works, but it only working moved to hide part.

FrameworkContentElement fce = (mycaret.Parent as FrameworkContentElement);
if (fce != null)
{
    fce.BringIntoView();
}

I got an other method in this below code.

System.Windows.Rect rc = currentline.GetCharacterRect(LogicalDirection.Forward);
rtb.ScrollToVerticalOffset(rc.Bottom + rtb.VerticalOffset - txtAppendValue.ViewportHeight);

It gives bottom up panning. So how can I get top down panning through this way?