As AB is all prior art, it is not necessary to give a specific circuit, and a block diagram can be used, but at least the connection mode between the output of A and the input of B (that is, how the circuit B is integrated into the electrical appliance A), the function of the output port of A and part of the function of the input port of B should be given.
It is best to give a detailed circuit diagram. You don't have to be completely clear about the function, just be clear about the function you invented.