Digital Electronics

Lecturer: Dr S.W. Moore

No. of lectures and practicals: 11 + 7

Aims

The aims of this course are to present the principles of combinational and sequential digital logic design and optimisation at a gate level. The use of transistors for interfacing and constructing gates is also introduced.

Lectures

• Introduction. The parts of a simple computer. Binary and representation of integers in binary. ASCII codes for characters. Switch logic.

• Boolean algebra. Truth tables and boolean algebra. Idealised logic gates and symbols. DeMorgan's rules. Logic to perform addition with ripple carry.

• Logic minimisation. Normal forms. Boolean cubes and Karnaugh maps for boolean optimisation.

• Complexities of logic design. Multilevel logic. An introduction to timing diagrams. Digital signals in the analog world. Hazards and hazard elimination. Fast carry propagation.

• Flip-flops. Memory elements, state and state diagrams. RS asynchronous flip-flop. Synchronous flip-flops: D, T and JK flip-flops. Setup and hold times.

• Synchronous state machines. More and Mealy finite state machines. Reset and self starting. State transition diagrams.

• Further state machines. State assignment and unique state encoding. One hot encoding. State minimisation.

• Asynchronous state machines. Fundamental mode machines and Muller C-elements. Asynchronous state machines in terms of RS flip-flops.

• Discrete components. Revision of resistance, Ohm's law and capacitance. Characteristics of diodes, NMOS and PMOS field effect transistors. NMOS and CMOS inverters. Rise and fall times. Voltage followers.

• Programmable logic. The structure and use of programmable logic arrays (PLAs). A brief introduction to FPGAs.

• Memories and interfaces. Use of SRAM and ROM: addressing, control signals, buses and tristate drivers.

Objectives

At the end of the course students should

• understand the relationships between combination logic and boolean algebra, and between sequential logic and finite state machines

• be able to design and minimise combinational logic

• appreciate tradeoffs in complexity and speed of combinational designs

• understand how state can be stored in a digital logic circuit

• understand the difference between asynchronous and synchronous logic

• know how to design a simple finite state machine from a specification and be able to implement this in gates and edge triggered flip-flops

• understand how to use MOS transistors

Recommended books

* Katz, R.H. (1994). Contemporary logic design, Benjamin/Cummings.
Hayes, J.P. (1993). Introduction to digital logic design. Addison-Wesley.

Books for reference

Mead, C. & Conway, L. (1980). Introduction to VLSI systems. Addison-Wesley (used in Part II VLSI).
Horowitz, P. & Hill, W. (1989). The art of electronics. Cambridge University Press (2nd ed.) (more analog).