ASIC vs FPGA
This page on ASIC vs FPGA describes difference between ASIC and FPGA.
ASIC contains rows of logic gates connected with wires. The wires are located between gate rows in a specific routing channels. ASIC stands for Application Specific Integrated Circuit.
FPGA is a programmable logic device.FPGA stands for Field Programmable Gate Array. FPGA contains CLBs (Configurable Logic Blocks), Input/Output blocks and inter-connection wires and switches.
FPGAs usually will have fast time to the market as no layout, mask processing and other manufacturing procedures are required. ASIC need all these.
FPGA can be reprogrammed on the field as needed but ASIC can not.
ASICs will possess all the capabilities as manufactured taking into consideration design specifications. Hence it will have small form factor, high clock speed compare to FPGA counterpart.
The circuit design flow is same in both the FPGA and ASIC. But both need different tools for implementation.FPGA need Xilinx ISE and ModelSim while ASIC need Synopsys design compiler(for synthesis) and Astro(for layout). Resulting circuit structures are different in both FPGA and ASIC.
The most popular FPGA implementation is carried on Xilinx Virtex LX50 Evaluation board. ASIC synthesis is done on ST 65nm CMOS design kit.
ASIC and FPGA Design Flow

Figure-1 depicts ASIC design flow. ASIC tools are generally driven by scripts.

Figure-2 depicts FPGA design flow. FPGA tools are generally GUI driven with push button flows. They too have scripting capabilities.
ASIC and FPGA Implementation Steps

Figure-3 depicts ASIC implementation flow.

Figure-4 depicts FPGA implementation flow.
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