These type of programmable devices are based on the basic structure equivalent to programmable logic array or PLA. Over the years, programmable arrays have increased in size and complexity. Highly configurable macrocells have been induced to enhance their flexibility and capability. Field-programmable gate array or FPGA has been developed with the concept of alternate architecture, to increase the effective size and to provide more functional flexibility in a single programmable device. The densities of FPGAs are much higher than any other PLDs. Each FPGA accommodates 1,200 to 20,000 equivalent gates whereas PLDs range in size from a few hundred to 2,000 equivalent gates.

An FPGA contains a number of relatively independent configurable logic modules, configurable I/Os and programmable interconnection paths or routing channels. All the resources of this device are uncommitted and these must be selected, configured, and interconnected by the user to form a logic system for his application. FPGAs are specified by their size, configuration of their logic modules, and interconnection requirements. FPGA with larger logic modules may not be sufficiently utilized to perform simple logic functions and thereby wasting the logic modules. Use of smaller logic modules leads to a larger number of interconnections with the device causing significant propagation delay as well as consuming a large percentage of FPGA area. The designer must optimize the logic module size and interconnection requirements according to the application of logic system design. For a given FPGA device, there are many possible ways to configure to meet the design requirements. Different types of FPGAs are available that differ in their architecture, technologies, and programming techniques.