A common misconception is that The Min Pin is the result of breeding smaller and smaller Dobermans. The truth is, these are two breeds completely separated even though they have some similarities. Dobermans have Rottweilers as their main ancestors.
But the Min Pin has the Dachshunds and the Italian Greyhounds as their ancestors.
There's speculation that they both descend from the German Pinscher, but there's no evidence to point that way. It seems that the fact that the Doberman and the Min Pin look similar is mere coincidence.