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## Digital Electronics

Lecturer: Professor I.M. Leslie (iml@cl.cam.ac.uk)

No. of lectures + practicals: 11 + 7

Aims

The aims of this course are to present the principles of combinational and sequential digital logic, to provide techniques for designing digital logic and to introduce basic physical electronics and MOS gate realisation.

Lectures

• Introduction, and combinational logic. The parts of a simple computer. Logic versus technology. Number representation. Boolean algebra. Idealised logic gates. Boolean algebra describes ideal combinational circuits. Normal forms. Simplification of combinational functions. Complexity in combination logic: adders. Dynamic behaviour of combination logic: hazards. Logic levels in real implementations.

• Sequential logic design. State. Finite state automata. State diagrams. Asynchronous and synchronous machines. Sequential logic, flip-flops and delays. Basis for a sequential machine. Fundamental and pulse mode. State assignment and state control. Race conditions. Designing with edge triggered devices. Synchronisation. State minimisation. Initial conditions. Examples.

• Technology. Requirements for logic implementation. Simple electricity. Semiconductors, holes and electrons, junctions, depletion layers. Devices and their properties. Diodes and MOS transistors. nMOS and CMOS circuits. Capacitance and rise and fall times. Output stages and bus arrangements. Fabrication of integrated circuits. Memory implementation and programmable logic.

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 edge triggered 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

• have a basic understanding of how CMOS technology works and what factors limit its speed of operation

Recommended books

Lewin, M.H. (1983). Logic Design and Computer Organization. Addison-Wesley (out of print).
Dowsing, R.D. & Woodhams, F.W.D. (1990). Computers from Logic to Architecture. Chapman and Hall.
Hayes, J.P. (1993). Introduction to Digital Logic Design. Addison-Wesley.