IEC 61523-3:2004

Overview

IEC 61523-3:2004 / IEEE 1497-2001 - Standard Delay Format (SDF) defines a textual, tool- and language-independent file format for representing delay and timing data across the electronic design process. SDF is an ASCII, human- and machine-readable format used to convey path delays, timing constraint values, interconnect delays and high‑level technology parameters for timing analysis, verification and annotation. Published as an IEC/IEEE dual‑logo standard, SDF enables consistent exchange of timing data between EDA tools and design teams.

Key Topics

• File structure and syntax: standardized header, cell definitions, labels and timing environment constructs (see Annexes for syntax and examples).
• Delay representation: path delays, interconnect delays and device delay entries represented in a portable ASCII format.
• Timing checks and constraints: constructs for specifying setup/hold checks, pulse width and other timing verification items.
• Annotation modes:
  • Back‑annotation - attaching measured or post‑layout delays to RTL/netlist for accurate timing analysis.
  • Forward‑annotation - passing timing constraints from analysis tools to synthesis, floorplanning or layout tools.
• Timing environments: support for multiple environments (different process, voltage, temperature corners) and multiple SDF files per design.
• Tool interoperability: designed for EDA tool implementers and for sharing timing data between vendors, leveraging the SDF conventions analogous to Verilog specify blocks.

Applications

SDF is widely used in electronic design automation (EDA) for:

• Timing verification and static timing analysis - applying back‑annotated delays to verify design timing margins.
• Post‑layout timing signoff - communicating layout/interconnect delays to logic simulation and timing tools.
• Design synthesis and floorplanning - forward‑annotating timing constraints to guide implementation.
• Cross‑tool data exchange - moving timing models between vendors, labs and design teams in a consistent, ASCII format. Typical users include EDA tool developers, ASIC/SoC design engineers, verification engineers, layout and synthesis tool chains, and timing analysts.

Related Standards

• IEC 61523 (series) - Part 1: Integrated circuit delay and power calculation systems; Part 2: Pre‑layout delay specification for CMOS ASIC libraries.
• IEEE 1497-2001 - original SDF publication (dual‑logo adoption as IEC 61523-3:2004).

SDF keywords: Standard Delay Format, SDF, timing data, delay back‑annotation, delay forward‑annotation, timing constraints, EDA interoperability, path delays, interconnect delays.