A latch or a flip-flop is a circuit that has two stable states and can be used to store state information. They typically constructed using feedback that crosses over between two arms of the circuit, to provide the circuit with a state. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic . Latches and flip-flops are fundamental building blocks of digital electronics systems used in computers, communications, and many other types of systems.
In addition to global negative feedback, amplifiers usually have some form of local negative feedback, but sometimes this is not as apparent. A cathode follower is an example of an amplifier stage with 100% negative feedback. This is what gives it the high input impedance and low output impedance, and the near-unity maximum gain. Some amplifiers will use a single-stage inverting amplifier circuit with local feedback from the plate to the grid via a large resistor and coupling cap. The gain of these inverting stages is set by the value of the feedback resistor in proportion to the value of the input resistor.