Xilinx FPGA vs Altera FPGA: A Comprehensive Comparison

1. Introduction to FPGA

FPGA, or Field - Programmable Gate Array, is a significant advancement in the field of programmable devices. It emerged as a semi - custom circuit solution in the ASIC domain, addressing the limitations of custom circuits and the restricted gate - circuit capacity of traditional programmable devices. FPGAs are based on the principle of lookup tables (LUTs), which are essentially RAMs. By altering the content of the LUTs through programming files, FPGAs can achieve different logic functions, enabling them to be reconfigured multiple times.

2. Structural Differences

2.1 Xilinx's Structure

Taking Spartan - II as an example, Xilinx's FPGA mainly consists of CLBs (Configurable Logic Blocks), I/O blocks, RAM blocks, and programmable interconnections. In Spartan - II, each CLB contains two Slices, and each Slice includes two LUTs, two flip - flops, and related logic such as carry logic, arithmetic logic, and storage logic. Slices are the basic units for implementing logic in Spartan - II. In newer generations, there are also 6 - input Slices. For instance, a 6 - input Slice includes 4 6 - input LUTs and 8 registers, with a significantly enhanced logic capacity compared to traditional 4 - input Slices.

2.2 Altera's Structure

Altera's FLEX/ACEX chips are structured with LABs (Logic Array Blocks), I/O blocks, EAB blocks (Embedded Array Blocks), and internal row - column interconnections. One LAB contains 8 LEs (Logic Elements), and each LE includes a LUT, a flip - flop, and dedicated related logic. Thus, the LE is the basic unit for implementing logic in Altera's FLEX/ACEX chips.

In summary, Xilinx interconnects at the CLB unit level, while Altera interconnects at the LAB unit level. The basic logic units are also different, with Xilinx using Slices and Altera using LEs.

3. Performance Comparison

3.1 Top - level Device Performance

In the comparison of top - level devices, Xilinx generally outperforms Altera in terms of speed and other performance metrics. Xilinx has been able to maintain a slight edge in providing high - performance solutions, which makes it a preferred choice for applications where high - speed operation is crucial.

3.2 Logic Resource Utilization and Routing

Xilinx has more abundant short - line resources compared to Altera. When the logic resources are fully utilized, Xilinx FPGAs are easier to route. However, due to the design of more short - line resources, the cost of Xilinx devices at the same speed grade and logic resource level is higher than that of Altera. This cost difference is reflected in the final selling price. Therefore, if Altera's FPGAs can meet the design requirements, they offer a higher cost - performance ratio.

4. Software and Development Tools

4.1 Xilinx's Tools

Xilinx offers the Vivado Design Suite, a leading FPGA development tool in the industry. It integrates functions such as synthesis, implementation, verification, and debugging. Vivado supports languages like VHDL, Verilog, and SystemVerilog, and also has features such as high - level synthesis (HLS) and support for Zynq programmable SoC development. Additionally, Xilinx's ISE has good script support, which is very useful for experienced users in large - scale design projects, allowing for more precise control and automation of backend design.

4.2 Altera's Tools

Altera uses the Quartus Prime tool. It supports languages including VHDL, Verilog, SystemVerilog, and OpenCL. Quartus Prime integrates design, simulation, verification, programming, and debugging functions, and is suitable for the design of Cyclone and Arria series FPGAs. Its integrated interface has better usability, making it easier for beginners to get started.

5. Application Areas

5.1 Xilinx's Application Areas

Xilinx's FPGAs are widely used in data centers and artificial intelligence fields. Their high - performance chips, such as those in the Virtex and Kintex series, are well - suited for handling complex algorithms and large - scale data processing in these areas. Xilinx also has a presence in aerospace military applications, as it offers aerospace - grade FPGAs, which Altera lacks.

5.2 Altera's Application Areas

Altera's FPGAs are more commonly used in communication, video, and graphics fields. The company's products, like the Cyclone and Arria series, are designed to meet the requirements of high - bandwidth data transmission and real - time processing in these applications.

6. Other Differences

6.1 Pin Definitions

There are significant differences in pin definitions between the two companies. In Altera, any pin can be connected to a signal like'sig' in the statement 'always @ (posedge(sig)) ……', but in Xilinx's FPGAs, only clk signals can be assigned such signals. Also, Altera's clk pins can only be used as inputs, while Xilinx's clk pins can be used as ordinary I/O pins when not used for clock input.

6.2 IO Structure

Altera's IO feature does not have pull - down resistors, while Xilinx's IO structure has both pull - up and pull - down resistors. For example, in a transmitter project where a low - level output is required upon power - on, using Altera's Cyclone 3 may result in a high - level output during the configuration process due to the tri - state and weak pull - up on the pins. In contrast, Xilinx's VII and V5 series can easily solve this problem by enabling the pull - down feature of the pins.

6.3 Power Requirements

Xilinx FPGAs generally require a very low power supply voltage, making them well - suited for low - power environments. On the other hand, Altera FPGAs need a relatively higher power supply voltage, which is a disadvantage in low - power applications.

In conclusion, both Xilinx and Altera are leading players in the FPGA market, each with its own unique features and advantages. When choosing between them, engineers and designers need to consider factors such as performance requirements, cost, development tool familiarity, and application areas to select the most suitable FPGA for their projects.