Hi Lofty, there is the standard turbo, and also the pressure wave supercharger (A hybrid device)
a normal turbo uses the expansion of exhaust gases to drive a turbine, the other end of the turbine is connected to another turbine that compresses the incoming air.. there is no connection between the exhaust gas and the incoming air.
The pressure wave device uses a common chamber and rotating vane, the pusles of exhaust gas compress a column of air for the inlet cycle, the chamber is designed so that even though the inlet air and exhaust gas share the chamber, the 2 exhaust gas is never re-inhaled. (or virtually never - some slight ingestion can actually be used to reburb any unburnt mixture to aid emissions (this is more commonly known as egr - or exhaust gas recirculation)
Joe