How latches work?

Answer 1

Computer Architectures - Digital Circuits - Latches and flip-flops

In the same way that gates are the building blocks of combinatorial circuits, latches and flip-flops are the building blocks of sequential circuits.

While gates had to be built directly from transistors, latches can be built from gates, and flip-flops can be built from latches. This fact will make it somewhat easier to understand latches and flip-flops.

Both latches and flip-flops are circuit elements whose output depends not only on the current inputs, but also on previous inputs and outputs. The difference between a latch and a flip-flop is that a latch does not have a clock signal, whereas a flip-flop always does.

Latches

How can we make a circuit out of gates that is not combinatorial? The answer is feed-back, which means that we create loops in the circuit diagrams so that output values depend, indirectly, on themselves. If such feed-back is positive then the circuit tends to have stable states, and if it is negative the circuit will tend to oscillate.

A latch has positive feedback. Here is an example of a simple latch: