class AB output stage

[liusupeng]

I see two types of class AB output stage. One of them is having PMOS on top and NMOS at the bottom. both transistors are common source configuration. the other one is having NMOS on top and PMOS at the bottom. both transistors are source follower configuration. Can any one tell me the advantage and disadvantages of each of these two configurations?

 

[checkmate]

The first is on common-source configuration. The advantage is gain and swing. The second is on source follower configuration, allowing for much lower output impedance for driving resistive loads.

 

[fcfusion]

Common source AB has much better linearity than source follower.

In source followers, there is a point were both transistor are cut off, near AVDD/2