7. Introduction to Sequential Circuits

Introduction to Sequential Circuits

Sequential circuits are a type of digital logic circuit where the output depends not only on the present input but also on the history of past inputs. This is in contrast to combinational circuits, where the output is solely a function of the present input.

Key Characteristics:

  • Memory Elements: Sequential circuits contain memory elements (like flip-flops) that store past input states.
  • Feedback Path: They have a feedback path that allows the circuit to "remember" previous states.
  • Clock Signal: Many sequential circuits are synchronized by a clock signal, which controls the timing of state changes.

Types of Sequential Circuits

 

Synchronous Sequential Circuits:

These circuits use a clock to synchronize the behavior of the flip-flops or memory elements. All state changes occur at the edge of the clock pulse.

  • These circuits use a clock signal to synchronize state changes.
  • The state changes only at specific times, typically at the rising or falling edge of the clock.
  • Examples: Counters, Shift Registers, Finite State Machines (FSMs).

Asynchronous Sequential Circuits:

  • These circuits do not use a clock signal; instead, state changes occur in response to input changes.
  • They are more complex to design and analyze due to potential race conditions and hazards.
  • Examples: Asynchronous counters, some types of FSMs.