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## Digital Electronics

This course is taken by Part IA (50% Option), Part II (General) and Diploma students.

Lecturer: Dr I.J. Wassell

No. of lectures and practical classes: 11 + 7

This course is a prerequisite for ECAD (Part IB) and VLSI Design (Part II).

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. 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.

• Introduction to practical classes. Use of prototyping box, breadboard and digital logic integrated circuits (ICs or chips).

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

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

• Memories and programmable logic. SRAM, ROM addressing, busses and control. Tri-state drivers. The structure and use of programmable logic arrays (PLAs). A brief introduction to FPGAs.

• 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. [2 lectures]

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

• 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

* Harris, D.M. & Harris, S.L. (2007). Digital design and computer architecture. Morgan Kaufmann.
Katz, R.H. (2004). Contemporary logic design. Benjamin/Cummings. The 1994 edition is more than sufficient.
Hayes, J.P. (1993). Introduction to digital logic design. Addison-Wesley.

Books for reference:

Horowitz, P. & Hill, W. (1989). The art of electronics. Cambridge University Press (2nd ed.) (more analog).
Weste, N.H.E. & Harris, D. (2005). CMOS VLSI Design - a circuits and systems perspective. Addison-Wesley (3rd ed.).
Mead, C. & Conway, L. (1980). Introduction to VLSI systems. Addison-Wesley (used in Part II VLSI).
Crowe, J. & Hayes-Gill, B. (1998). Introduction to digital electronics. Butterworth-Heinemann.
Gibson, J.R. (1992). Electronic logic circuits. Butterworth-Heinemann.

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