FPGA to ASIC: A Practical Transition to Silicon

FPGA to ASIC: A Practical Transition to Silicon

From Prototype to Production

In the world of digital design, Field-Programmable Gate Arrays (FPGAs) and Application-Specific Integrated Circuits (ASICs) represent two ends of a spectrum — one offering flexibility, the other offering performance and efficiency.

• FPGAs are reconfigurable chips, ideal for prototyping and validation.

• ASICs are custom-built chips, optimized for mass production.

The journey from FPGA to ASIC marks the moment when an idea becomes a permanent, silicon-based product.

This transition is more than just technology—it’s a strategic step that can transform a functional prototype into a cost-effective, high-performance commercial chip.

1. FPGA vs. ASIC: Understanding the Difference

In short:
FPGAs are for experimentation, ASICs are for execution.

2. Why Transition from FPGA to ASIC?

Many projects begin with FPGAs because they:

• Allow rapid prototyping and debugging

• Enable real-time verification of algorithms

• Avoid expensive fabrication risks

However, as a product matures, FPGAs may hit limits in:

• Power efficiency (especially for portable devices)

• Performance (due to programmable routing overhead)

• Unit cost (for high-volume manufacturing)

That’s when ASICs make sense.

Typical transition triggers:

1. Production volume exceeds ~10,000 units.

2. Power or performance goals exceed FPGA capability.

3. Form factor or cost constraints tighten.

4. Long-term product stability is required (no reprogrammable parts).

3. The FPGA-to-ASIC Transition Flow

Transitioning from FPGA to ASIC involves reusing much of your existing design — but with deeper physical and timing considerations.

Here’s a step-by-step roadmap:

Step 1: RTL Refinement

Your FPGA design (written in Verilog/VHDL) becomes the foundation of the ASIC.

However, FPGA RTL often contains:

• Vendor-specific primitives (like Xilinx DSP48 or Intel ALM blocks)

• Proprietary IPs (like PLLs, block RAMs)

• Behavioral shortcuts that don’t map well to ASICs

Actions:

• Replace FPGA-specific blocks with technology-independent RTL.

• Re-architect memory using ASIC SRAM macros.

• Substitute clock managers and IOs with ASIC equivalents.

Think of this stage as making your RTL “portable” — clean, generic, and synthesis-friendly.

Step 2: ASIC Design Flow Integration

After RTL refinement, the ASIC design flow begins. It’s more rigorous than FPGA design and includes synthesis, physical design, and verification.

ASIC Flow Overview:

1. RTL → Logic Synthesis (using Synopsys Design Compiler or Cadence Genus)

2. Gate-level Netlist Generation

3. Static Timing Analysis (STA)

4. Place & Route (Physical Design)

5. Layout Verification (DRC, LVS)

6. Tape-out (mask generation)

FPGA engineers entering this world must learn timing closure, clock tree synthesis, and power domain management — all crucial for silicon success.

Step 3: Technology Mapping

FPGA LUTs and flip-flops are replaced with ASIC standard cells from a technology library.

ASIC libraries are process-dependent — each foundry (TSMC, GlobalFoundries, Samsung) provides optimized cell sets.

Step 4: Timing and Power Optimization

FPGAs abstract much of timing; ASICs require explicit timing closure.

Key timing issues to manage:

• Setup and hold times

• Clock skew and jitter

• Interconnect delay

Power optimization involves:

• Clock gating

• Multi-Vt (threshold voltage) libraries

• Dynamic Voltage and Frequency Scaling (DVFS)

• Power gating for inactive blocks

ASIC tools allow fine-grained control over each transistor, enabling dramatic power savings — often 10×–100× better than FPGA equivalents.

Step 5: Physical Design and Verification

Physical design transforms the netlist into a layout — a geometric representation of the circuit.

Steps include:

• Floorplanning — defining block locations.

• Placement — arranging standard cells.

• Routing — connecting all cells with metal layers.

• Clock Tree Synthesis (CTS) — ensuring uniform clock distribution.

• Signoff Verification — DRC (Design Rule Check), LVS (Layout vs. Schematic), and IR drop analysis.

Finally, the GDSII file (layout database) is generated and sent to the foundry for tape-out.

Step 6: Fabrication and Testing

ASIC fabrication involves multiple layers of photolithography, etching, and doping on silicon wafers.
After manufacturing, each chip is:

• Packaged into its final form factor (QFN, BGA, etc.)

• Tested for defects using ATE (Automatic Test Equipment)

• Characterized across voltage and temperature corners

This is followed by bring-up and validation — running the chip in its target environment for real-world verification.

4. FPGA vs. ASIC Design Challenges

ASIC design introduces new domains: DFT (Design for Test), DFM (Design for Manufacturability), and yield optimization — essential for large-scale production.

5. Design for Test (DFT): Ensuring Reliability

Since ASICs are fixed once fabricated, testing is critical.
DFT techniques ensure you can detect faults after fabrication.

Common DFT methods:

• Scan Insertion – Adds scan chains to check flip-flop states.

• BIST (Built-In Self-Test) – Automatically tests memories and logic.

• JTAG (IEEE 1149.1) – Standard boundary scan interface.

DFT design ensures chips can be tested quickly and reliably during manufacturing — a must for commercial-grade ASICs.

6. Verification: The Cornerstone of ASIC Success

Verification complexity grows dramatically when moving from FPGA to ASIC.

ASIC verification includes:

• Functional simulation (behavioral correctness)

• Formal verification (mathematical equivalence)

• Gate-level simulation (timing accuracy)

• Static timing analysis

• Power-aware simulation

Modern ASIC verification leverages SystemVerilog UVM (Universal Verification Methodology) and coverage-driven testing to ensure every logic path is validated before tape-out.

7. Economic Considerations

Thus, the FPGA-to-ASIC transition only makes sense for medium to high-volume products — or when performance/power needs justify it.

8. Tools and Platforms for FPGA-to-ASIC Migration

Additionally, OpenLane and SkyWater 130 nm PDK provide open-source flows for academic and startup experimentation.

9. Practical Tips for a Smooth Transition

1. Clean RTL early. Avoid vendor-specific macros.

2. Use parameterized modules. Easier to retarget in ASIC.

3. Separate clock/reset logic. ASIC timing is more sensitive.

4. Plan for DFT upfront. Retrofits are costly.

5. Run static linting tools. Catch synthesizability issues.

6. Prototype ASIC logic on FPGA. Great for functional verification.

7. Engage foundry PDK teams early. Ensure compatibility and DRC compliance.

10. The Future: FPGA + ASIC Hybrid Ecosystems

The boundary between FPGA and ASIC is blurring:

• Structured ASICs and eASICs offer midpoints (customizable metal layers).

• Chiplet architectures integrate FPGA tiles and ASIC dies in one package.

• AI-assisted design automation accelerates FPGA-to-ASIC migration.

These innovations shorten the transition cycle — enabling startups to move from prototype to production faster than ever before.

From Reconfigurable to Real Silicon

Transitioning from FPGA to ASIC is a rite of passage for digital design engineers — it transforms ideas into tangible products.
It’s a journey from flexibility to finality, from bits to atoms.

Mastering this process means understanding:

• Design portability

• Physical and timing constraints

• Verification and test strategies

• Economics of scale

With today’s open-source EDA ecosystems and accessible foundry programs, the FPGA-to-ASIC path is no longer reserved for semiconductor giants — it’s open to startups, researchers, and innovators alike.

The world’s most powerful chips often start on an FPGA.
But their destiny — and true potential — lies in custom silicon.

VLSI Expert India: Dr. Pallavi Agrawal, Ph.D., M.Tech, B.Tech (MANIT Bhopal) – Electronics and Telecommunications Engineering