Less complex devices such as simple programmable logic devices (SPLDs) and complex programmable logic devices (CPLDs) bridge the gap between discrete logic devices and entry-level FPGAs.Įntry-level FPGAs emphasize low power consumption, low logic density and low complexity per chip. Originally, FPGAs included the blocks in Figure 1 and little else, but now designers can choose from products with a large range of features. Mux 6 determines whether the operation is asynchronous or synchronized to the FPGA clock via the D flip-flop.Ĭurrent-generation FPGAs include more complex CLBs capable of multiple operations with a single block CLBs can combine for more complex operations such as multipliers, registers, counters and even digital signal processing (DSP) functions. Mux 4 selects between the FA output or the LUT output. In normal mode, the LUTs are combined with Mux 2 to form a four-input LUT in arithmetic mode, the LUT outputs are fed as inputs to the FA together with a carry input from another CLB. This simplified CLB has two modes of operation. The number and arrangement of components in the CLB varies by device the simplified example in Figure 2 contains two three-input LUTs (1), an FA (3) and a D-type flip-flop (5), plus a standard mux (2) and two muxes, (4) and (6), that are configured during FPGA programming. Input/output (I/O) blocks interface between the FPGA and external devices.ĭepending on the manufacturer, the CLB may also be referred to as a logic block (LB), a logic element (LE) or a logic cell (LC).įigure 2: A simplified CLB: The four-input LUT is formed from two three-input units. FPGA ArchitectureĪ basic FPGA architecture ( Figure 1) consists of thousands of fundamental elements called configurable logic blocks (CLBs) surrounded by a system of programmable interconnects, called a fabric, that routes signals between CLBs. FPGA manufacturers include Intel, Lattice Semiconductor, Microchip Technology and Microsemi. In contrast, FPGA stores its configuration information in a re-programmable medium such as static RAM (SRAM) or flash memory. These devices could be programmed either at the factory or in the field, but they used fuse technology (hence, the expression “burning a PROM”) and could not be changed once programmed. The FPGA has its roots in earlier devices such as programmable read-only memories (PROMs) and programmable logic devices (PLDs). The interconnects can readily be reprogrammed, allowing an FPGA to accommodate changes to a design or even support a new application during the lifetime of the part. Field Programmable Gate Array (FPGA) is an integrated circuit that consists of internal hardware blocks with user-programmable interconnects to customize operation for a specific application.
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