Description
The unit introduces the two main branches of digital electronics, combinational and sequential. Thus, the student gains familiarity in the fundamental elements of digital circuits, notably different types of logic gates and bistables. The techniques by which such circuits are analysed, introduced and applied, including Truth Tables, Boolean Algebra, Karnaugh Maps, and Timing Diagrams.
The theory of digital electronics has little use unless the circuits can be built – at low cost, high circuit density, and in large quantity. Thus the key digital technologies are introduced. These include the conventional TTL (Transistor-Transistor Logic) and CMOS (Complementary Metal Oxide Semiconductor). Importantly, the unit moves on to programmable logic, including the Field Programmable Gate Array (FPGA). Finally, some standard digital subsystems, which become important elements of major systems such as microprocessors, are introduced and evaluated.
On successful completion of this unit students will have a good grasp of the principles of digital electronic circuits, and will be able to proceed with confidence to further study.
Learning Outcomes
By the end of this unit students will be able to:
1. Explain and analyse simple combinational logic circuits.
Concepts of combinational logic:
Simple logic circuits implemented with electro-mechanical switches and transistors. Circuits built from AND, OR, NAND, NOR, XOR gates to achieve logic functions, e.g. majority voting, simple logical controls, adders
Number systems, and binary arithmetic:
Binary, Decimal, Hexadecimal number representation, converting between, applications and relative advantages. Addition and subtraction in binary, range of n-bit numbers
Analysis of logic circuits:
Truth Tables, Boolean Algebra, de Morgan’s theorem, Karnaugh Maps
Simplification and optimisation of circuits using these techniques
2. Explain and analyse simple sequential logic circuits.
Sequential logic elements and circuits:
SR latch built from NAND or NOR gates
Clocked and edge-triggered bistables, D and JK types
Simple sequential circuits, including shift registers and counters
Timing Diagrams
Memory technologies:
Memory terminology, overview of memory technologies including Static RAM, Dynamic RAM and Flash memory cells
Relative advantages in terms of density, volatility and power consumption
Typical applications, e.g. in memory stick, mobile phone, laptop
3. Describe and evaluate the technologies used to implement digital electronic circuits.
Logic values represented by voltages:
The benefit of digital representation of information
The concept of logic input and output values and thresholds
Digital technologies:
Introduction to discrete logic families, CMOS and TTL, relative advantages in terms of speed, power consumption, density
Programmable logic, FPGAs, relative advantages and applications
4. Describe and analyse a range of digital subsystems, hence establishing the building blocks for larger systems.
User interface:
Examples to include switches, light emitting diodes and simple displays
Digital subsystems:
Examples to be drawn from adders (half, full, n-bit), multiplexers and demultiplexers, coders and decoders, counters applied as timers, shift registers applied to serial data transmission, elements of the ALU (Arithmetic Logic Unit).
Emphasis on how these can be applied, and how they might fit into a larger system