Digital Circuits/Digital Circuit Types

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Digital circuit: A digital circuit is a circuit where the signal must be one of two discrete levels. Each level is interpreted as one of two different states (for example, on/off, 0/1, true/false). Digital circuits use transistors to create logic gates in order to perform Boolean logic. This logic is the foundation of digital electronics and computer processing. Digital circuits are less susceptible to noise or degradation in quality than analog circuits. It is also easier to perform error detection and correction with digital signals. To automate the process of designing digital circuits, engineers use electronic design automation (EDA) tools, a type of software that optimizes the logic in a digital circuit.

The goal of this text is to review the design techniques for digital circuits starting from NAND gates and Boolean Algebra. The end result is a student should be able to design these types of circuits:

  • Combinational Logic Circuits directly respond to input change
  • Sequential Networks remember the present state and combine with input changes to create a new state
  • Synchronous Sequential Network Design (Mealy and Moore) is a method of designing complex sequential logic circuits that only look at inputs at times determined by a clock. This results in circuits with fewer glitches, more predictability but are slower and use more hardware.
  • Asynchronous Sequential Network Design is a method of designing complex sequential logic circuits that are very fast, simple and respond to inputs at speeds determined by the devices themselves rather than a clock. They are harder to design but are closer to nature (including to brain operation)