Manufacture of integrated circuits

An integrated circuit design is constructed from a library of standard cells, at least some of which are available in different sizes having different input requirements, output capabilities and response times. Details of a proposed integrated circuit design are entered into a computer which stores the properties of the standard cells. The computer selects among the standard cells required in the proposed design for compatible sizes of the cells providing the smallest circuit or the fastest circuit. The computer can also check race conditions in the circuit and that input and output criteria are satisfied. When a satisfactory design has been reached its details are produced as an output which is used to produce layout diagrams from which the integrated circuit is manufactured.