FPGAs Vs ASICs

Basically Field Programmable Gate Arrays(FPGAs) and Application Specific ICs(ASICs) are Programmable Logic Devices(PLDs). Difference between ASICs and FPGAs mainly depends on costs, tool availability, performance and design flexibility. They have their own pros and cons.A comparison of the advanatages and disadvantages of both of them are given below.

FPGA Design Advanatages

• Faster time-to-market: No layout, masks or other manufacturing steps are needed for FPGA design. Readymade FPGA is available and developer can directly burn the HDL code.
  

• No NRE (Non Recurring Expenses): This cost is typically associated with an ASIC design. For FPGA this is not there. FPGA tools are cheap. Sometimes its free. ASIC youpay huge NRE and tools are expensive.
  

• Simpler design cycle: This is due to software that handles much of the routing, placement, and timing. Manual intervention is less.The FPGA design flow eliminates the complex and time-consuming floorplanning, place and route, timing analysis.

• More predictable project cycle: The FPGA design flow eliminates potential re-spins of the project since the design logic is already synthesized and verified in FPGA device.

• Field Reprogramability: A new program can be uploaded remotely, instantly. FPGA can be reprogrammed in a snap while an ASIC can take a huge amount of money and time to make the same changes. FPGA costs start from a couple of dollars to several hundreds or more depending on the hardware features.

• Reusability: Reusability of FPGA is the main advantage. Prototype of the design can be implemented on FPGA which could be verified for almost accurate results so that it can be implemented on an ASIC. If design has faults change the HDL code, generate bit stream, program to FPGA and test again.Modern FPGAs are reconfigurable both partially and dynamically.

• FPGAs are good for prototyping and limited production.If you are going to make 100-200 boards it isn't worth to make an ASIC.

• Generally FPGAs are used for lower speed, lower complexity and lower volume designs. But today's FPGAs even run at 500 MHz with superior performance. With unprecedented logic density increases and a host of other features, such as embedded processors, DSP blocks, clocking, and high-speed serial at ever lower price, FPGAs are suitable for almost any type of design.

• Unlike ASICs, FPGA's have special hardwares such as Multiply and Accumulator modules (MACs) , memories and highspeed I/O, embedded CPU etc inbuilt, which can be used to get better performace. Modern FPGAs are packed with features. Advanced FPGAs usually come with phase-locked loops, low-voltage differential signal, clock data recovery, more internal routing, high speed, hardware multipliers for DSPs, memory,programmable I/O, IP cores and microprocessor cores. Power PC (hardcore) and Microblaze (softcore) in Xilinx and ARM (hardcore) and Nios(softcore) in Altera are examples. There are FPGAs available now with built in ADC. Using all these features designers can build a system on a chip.
  

FPGA Design Disadvanatges

• Powe consumption in FPGA is more. You don't have any control over the power optimization. This is where ASIC wins the race.
  

• You have to use the resources available in the FPGA. Thus FPGA limits the design size.

• Good for low quantity production. As quantity increases cost per product increases compared to the ASIC implementation.

ASIC Design Advantages

• Lower unit costs: For very high volume designs costs comes out to be very less. Larger volumes of ASIC design proves to be cheaper than implementing design using FPGA.

• ASICs are faster than FPGA: ASIC gives design flexibility. This gives enoromous opportunity for speed optimizations.

• Low power: ASIC can be optimized for required low power. There are several low power techniques such as power gating, clock gating, multi vt cell libraries, pipelining etc are available to achieve the power target. This is where FPGA fails badly !!! Can you think of a cell phone which has to be charged for every call.....never.....low power ASICs helps battery live longer life.
  

• In ASIC you can implement analog circuit, mixed signal designs. This is generally not possible in FPGA.

• In ASIC DFT (Design For Test) is inserted. In FPGA DFT is not carried out.

ASIC Design Disadvantages

• Time-to-market: Some large ASICs can take a year or more to design. A good way to shorten development time is to make prototypes using FPGAs and then switch to an ASIC.

• Design Issues: Signal Integrity isuues and many more. In FPGA you don't have all these because ASIC designer takes care of all these. ( Don't forget FPGA is an IC and designed by ASIC design enginner !!)

• Expensive Tools: ASIC design tools are very much expensive. You spend a huge amount of NRE.

A good article (more technical one) comparing each factors determining the selection fo ASICs and FPGAs is available here:

http://www.soccentral.com/results.asp?CategoryID=488&EntryID=15887

Note: Analysis , Synthesis, floorplanning, place and route, timing analysis and verification are some of the steps in the design flow of ICs. Will explain about these steps in some other post.