This is typically a vacuum tube phase inverter topology, but the same principles apply to transistors. How it works, well one bias chain is AC grounded, and the other part of the topology works in a normal common emitter mode. When the common emitter circuit raises the output voltage, the current on the emitter constant current source falls. By falling it allows the other stage's current to rise by exactly the same value, thus inverting thr output. Perfect symmetry is obtained when both stages are connected to a constant current source.
