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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

**Recommended reading**

* 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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