What is Xilinx Spartan FPGA?

Xilinx Spartan field programmable gate arrays (FPGAs) are integrated circuits that can be configured by engineers and designers to implement custom digital logic functions. The Spartan family provides an affordable and scalable alternative to high-end Virtex FPGAs for applications with lower complexity.

This article provides a comprehensive overview of Xilinx Spartan FPGAs covering their architecture, design methodology, available features, key benefits, target applications and examples of real-world usage across various industries.

Introduction to Xilinx Spartan FPGAs

Xilinx first introduced the Spartan FPGA product line in 1997 to address applications with gate counts between 10K and 100K. The Spartan series has the following defining characteristics:

• Cost-optimized architecture by removing advanced features of Virtex FPGAs
• Lower power consumption due to smaller chip size and optimized design
• Reduced pin counts and smaller packages
• Built-in hardcore blocks like memory controllers and processors
• Support for 3.3V and 1.8V board voltages
• Programming using low-cost cables and interfaces
• Target applications in embedded electronics, IoT, consumer devices

Newer Spartan families also integrate advanced capabilities like DSP blocks, PCI Express, integrated ARM cores and high-performance memory interfaces required in modern embedded systems.

Over successive generations, the Spartan architecture has achieved optimal balance between programmable logic performance, abundant I/Os and competitive pricing. This combination has resulted in the enormous popularity of Spartan FPGAs across a range of industries and applications globally.

Spartan FPGA Architecture

The Spartan architecture consists of three fundamental configurable elements:

1. Configurable Logic Blocks (CLBs) – The basic logic cell used to implement logic gates and datapath functions
2. Programmable I/O Blocks – Enables interfacing to external devices and systems
3. Programmable Interconnects – Wiring network connecting logic and I/O blocks

Configurable Logic Blocks

The core programmable logic capability in Spartan FPGAs is provided by standardized CLBs (Configurable Logic Blocks). Each CLB includes:

• 4 to 6 LUTs (Look Up Tables) – provide boolean logic functionality
• 8 flip-flops per LUT for sequential logic
• Arithmetic carry logic for multi-bit functions

By customizing the LUT programming and connecting flip-flops, complex logic functionality can be implemented using CLBs. The number of CLBs in a Spartan device depends on its density and can range from a few hundreds to tens of thousands.

Programmable I/O Blocks

Spartan FPGAs provide flexible interfacing to external signals through programmable I/O blocks surrounding the periphery of the device. Key characteristics include:

• Support for common I/O standards like LVTTL, LVCMOS, LVDS
• High speed 3.3V HSTL and SSTL memory interfaces
• Differential I/O for noise immunity
• Programmable drive strength and delay/rise/fall times
• On-die termination (ODT) for memory interfaces

Based on PCB interface requirements, each I/O pin can be customized independently for optimal signal quality.

Programmable Interconnect

Spartan FPGAs utilize a hierarchy of versatile programmable interconnects for wiring logic blocks together into a functional system:

• Local routing directly connects adjacent logic elements
• Global horizontal and vertical routing enables long distance connections
• I/O routing connects I/O pins to internal logic
• Fast carry chains rapidly propagates arithmetic carries between CLBs

Such flexible connectivity is made possible due to the programmable nature of FPGAs, which allows implementing any routing scheme digitally.

Embedded Hard IP Cores

In addition to the fundamental CLB, I/O and interconnect fabric, many Spartan families also integrate on-chip memory and processing through dedicated blocks including:

• Embedded block RAM (BRAM) – provides fast local data storage close to logic
• Digital signal processing (DSP) slices – for arithmetic intensive functions
• MicroBlaze soft processor – enables programmable software control
• Multi-port memory controllers – interfaces external memories like DDR SDRAM
• Serial transceivers – enables high speed interfacing for protocols like PCIe, Ethernet, USB etc.
• Analog-to-digital converters (ADCs) – allows analog data acquisition

These hardened blocks boost system performance while reducing cost and complexity of additional external components.

Spartan Product Families

Xilinx has released several successive generations of Spartan FPGA product families as the technology evolved over the last two decades:

Spartan-3 – The first high performance Spartan family featuring 90nm node, integrated DSP slices and abundant I/Os for interfacing.

Spartan-3E – Low cost optimized variant with reduced power consumption.

Spartan-3A/3A DSP – Automotive and industrial grade variants with -40°C to +125°C temperature rating.

Spartan-6 – Modernized Spartan built on a 45nm low-power process with 6.5 Gbps transceivers.

Spartan-7 – Latest Spartan family using 28nm technology with PCI Express interface support.

Each generation expanded capabilities and performance envelopes compared to prior versions for catering to evolving application requirements and fabrication technology improvements.

Within each Spartan family, there are multiple device density options providing different amounts of programmable resources. This flexible scaling allows matching device size to target application needs for optimization of utilization and costs.

Spartan FPGA Design Flow

Designing systems using Spartan FPGAs involves:

1. Design entry – Creating the desired logic functionality using schematics or HDL code (Verilog or VHDL). Xilinx’s Vivado Design Suite provides the development environment.
2. Simulation – Simulating the functionality using testbenches to verify intended behavior before implementation.
3. Synthesis – The HDL code is synthesized to produce a logical representation using the FPGA’s library primitives.
4. Implementation – Device-specific netlists are generated that map design to physical Spartan resources.
5. Programming – The final bitstream is generated for configuring the Spartan FPGA to implement the design.
6. In-system verification – Operation of programmed Spartan device is validated in the complete system context.

FPGA’s programmable nature enables verifying and optimizing the implementation iteratively until all functional and performance criteria are met. Once successfully prototyped, the same design can be seamlessly migrated to high volume production.

Key Benefits of Spartan FPGAs

Some major benefits of using Xilinx’s Spartan family for digital systems are:

• Cost-efficient – Spartan’s well-balanced architecture removes unneeded advanced features enabling very cost competitive pricing.
• Low power – Smaller Spartan FPGAs dissipate less static and dynamic power which reduces cooling needs.
• Reduced BOM – Integrated memory and processing blocks minimize external IC count.
• Flexible I/O – Wide range of interfacing standards allows matching PCB-level signals.
• Scalability – Multiple Spartan density options available within each FPGA family.
• Easy programming – Low-cost tools and interfaces facilitates rapid prototyping.
• Accelerated time-to-market – FPGA’s reprogrammability accelerates system development and design iterations.
• Design security – FPGA configuration bitstream provides inherent IP protection against cloning.

For applications needing moderate programmable logic capability along with essential peripherals like interfacing, memory and DSP, Spartan provides the ultimate blend of capabilities and affordability.

Target Applications

Some major application areas where Spartan FPGAs are commonly used include:

Industrial Automation

• Motor drives
• Industrial sensors
• PLC systems
• Process controllers

Automotive Electronics

• RADAR systems
• Driver assistance systems
• Infotainment systems
• Telematics gateways

Aerospace and Defense

• GPS navigation
• RADAR and Sonar signal processing
• Video tracking systems
• Encryption/decryption

Instrumentation

• Data acquisition systems
• Protocol bridging
• Video test generators
• Mixed signal analysis

Consumer Electronics

• IoT edge nodes
• Wearables
• Appliance control
• Wireless communications

From mission critical guidance systems to high volume consumer goods, Spartan FPGAs deliver the flexibility, performance and reliability needed at aggressive price points.

Real-World Spartan FPGA Applications

Here are some examples highlighting the diverse real-world applications leveraging Xilinx’s Spartan family:

Industrial Motor Control

Spartan-6 FPGAs are widely used for controlling high power industrial motors. Key functions implemented include closed loop control, safety mechanisms and communication interfaces. Spartan’s integrated ADCs allow easy interface to position/speed sensors.

5G Wireless Baseband Processing

Spartan’s low power consumption enables cellular baseband processing for 5G remote radio heads deployed in places like stadiums and malls. Signal modulation, encoding and filtering algorithms run efficiently on Spartan’s DSP slices.

Automotive Driver Assistance

Spartan 7 FPGAs perform real-time processing of camera and RADAR feeds for advanced driver assistance applications like pedestrian detection, lane keeping and forward collision warning.

Space Satellite Payloads

Spartan’s radiation tolerant automotive grade FPGAs are deployed in satellite payloads for functions like data multiplexing, payload control and interfacing with communication buses.

Consumer Wireless Access Points

Spartan 3A DSP enables software defined radio capability in consumer grade WiFi access points. Flexible air interface protocols are implemented leveraging Spartan’s programmability coupled with high speed DSP blocks.

High Resolution Medical Imaging

Spartan 6 FPGAs perform image reconstruction algorithms for MRI, CT and ultrasound scanners. Parallel processing capability accelerates image generation from sensor data.

This demonstrates the wide applicability of Spartan FPGAs across diverse market segments thanks to their unique balance of capabilities, modularity and affordability.

Comparing Spartan vs. Virtex FPGA Lines

Xilinx’s higher tier Virtex FPGA line offers more advanced architectural features compared to Spartan series:

Programmable Logic

• Higher density of logic cells
• More LUTs and flip-flops per CLB
• Fast FPGA interconnect using longer lines
• Advanced 3D fabric with stacked silicon interconnect

Hardened Blocks

• Up to 100Gbps transceivers
• Integrated ARM processors up to 16 cores
• More BRAM and larger capacity DDR controllers
• High speed AMS interfaces like PCIe Gen5, CCIX, Ethernet, Interlaken

Reliability

• Extended -2 to 100oC temperature range
• Up to 1000K rad(Si) radiation tolerance
• SEU mitigation techniques

Software and IP

• Advanced Vivado design tools
• Broad portfolio of optimized IP cores

This superior performance, capacity and reliability comes at a significant cost premium over Spartan. Virtex FPGAs are geared for high complexity systems requiring absolute max throughput and bulletproof robustness like core routing and switching equipment.

Spartan FPGAs address applications where cost is a key factor but balanced features and reasonable performance is still needed like IoT, industrial controls, experimental research and entry level aerospace/defense projects.

Conclusion

For over 25 years, Xilinx’s Spartan family has delivered enormous value to the electronics industry by making FPGAs accessible to much wider range of applications where a balanced tradeoff between capabilities and costs is required.

Spartan FPGAs now integrate key peripherals like communication interfaces, embedded memory, DSP blocks along with abundant I/Os to interface the analog world. These elements multiply the utility of Spartan’s flexible programmable fabric for solving some of the most complex and demanding challenges across automation, defense, consumer and industrial market segments both today and tomorrow.

Frequently Asked Questions

Q: What are the key characteristics of Xilinx Spartan FPGAs?

A: Spartan FPGAs provide a cost-optimized, lower power FPGA option by removing unneeded advanced features. They target applications needing 10K to 100K logic gates.

Q: What are the main configurable elements in a Spartan FPGA?

A: Configurable logic blocks (CLBs) for implementing digital logic, flexible I/O blocks for interfacing signals and programmable interconnect for wiring it together.

Q: What embedded blocks are integrated in newer Spartan FPGAs?

A: Newer Spartan families include embedded RAM, DSP slices, ARM processors, memory controllers, ADC/DAC, high speed serial transceivers etc.

Q: How are designs implemented on a Spartan FPGA?

A: Using Xilinx’s Vivado tool, engineers can design at RTL or gate level, simulate functionality, synthesize into FPGA primitives and generate final bitstreams.

Q: When should Spartan FPGAs be chosen over higher-end Virtex FPGAs?

A: Spartan offers better cost-performance tradeoff for applications not needing the ultimate in speed, density and ruggedness offered by premium Virtex families.