Looking for books on the history of the Franks

More specifically I'm asking for suggestions on:

1. The Merovingian kingdom
2. The Carolingian kingdom
3. Specifically Charlemagne and the aftermath of his death

I'm mostly interested in the 8th and 9th centuries, but would love an introduction starting from the Merovingians, leading to the Carolingians, and culminating in the life and death of Charlemagne.

Any help is much appreciated.