Flip-Flop Using CMOS NAND Gates

Using just two NAND or inverter gates its possible to build a D type (or ‘toggle’) flip-flop with a pushbutton input.At power-up the output of gate N2 is at a logical ‘1’, ensuring that transistor T2 is switched off. When the pushbutton is pressed the output of N2 changes to a logical ‘0’ and transistor T2 conducts. The coupling between N1 and N2 ensures that the output of N1 will always be the inverse of N2 so T1 and T2 will always be in opposite states and will flip each time the pushbutton is pressed.