E-Books →Nano Electronics and Sensors

microprocessors, and (3) logic. Memory devices store random information such as the contents of a spreadsheet or database. Microprocessors execute software instructions to perform a wide variety of tasks such as running a word processing program or video game. Logic devices provide specific functions, including devicetodevice interfacing, data communication, signal processing, data display, timing and control operations, and almost every other function a system must perform.
Logic devices can be classified into two broad categories - (i) fixed and (ii) programmable. As the name suggests, the circuits in a fixed logic device are permanent, they perform one function or set of functions once manufactured, they cannot be changed. On the other hand, programmable logic devices (PLDs) are standard, offtheshelf parts that offer customers a wide range of logic capacity, features, speed, and voltage characteristics and these devices can be changed at any time to perform any number of functions. With fixed logic devices, the time required to go from design, to prototypes, to a final manufacturing run can take from several months to more than a year, depending on the complexity of the device. And, if the device does not work properly, or if the requirements change, a new design must be developed. The upfront work of designing and verifying fixed logic devices involves substantial "nonrecurring engineering" costs, or NRE. NRE represents all the costs customers incur before the final fixed logic device emerges from a silicon foundry, including engineering resources, expensive software design tools, expensive photolithography mask sets for manufacturing the various metal layers of the chip, and the cost of initial prototype devices. These NRE costs can run from a few hundred thousand to several million dollars.