15.2 Design for Testability
2 min read•july 25, 2024
() is a crucial aspect of digital circuit design. It involves adding extra hardware and techniques to make testing easier, improving and reducing . This approach is essential for efficient manufacturing and .
Key DFT techniques include , (), and . Early consideration of testability reduces design iterations, lowers test costs, and improves product quality. Implementing DFT principles involves analyzing designs, incorporating test structures, and using automation tools.
Design for Testability Fundamentals
Concept of design for testability
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- Enhances testing ease of digital circuits by incorporating additional hardware and design techniques
- Improves fault coverage and reduces test time leading to more efficient manufacturing processes
- Enables detection and diagnosis of manufacturing defects through various test methods (functional, structural, parametric testing)
- Facilitates integration of complex systems-on-chip (SoC) and IP blocks
- Supports and extending product lifecycle management
Key techniques in DFT
- Scan chain design converts flip-flops into scan cells forming shift register for test pattern application and response capture
- Built-in self-test (BIST) integrates and on-chip reducing external test equipment dependence (Logic BIST, Memory BIST)
- Boundary scan (IEEE 1149.1 JTAG) provides access to I/O pins and internal nodes supporting board-level interconnect testing
- selectively scans subset of flip-flops reducing area overhead while maintaining testability
- adds control and observation points improving overall circuit testability
- and facilitate post-silicon validation and debugging processes
Importance of early testability considerations
- Reduces design iterations and time-to-market accelerating product development cycles
- Lowers overall test cost by simplifying test generation and application processes
- Improves fault coverage and diagnostic resolution enhancing product quality
- Enables easier integration of IP blocks and system-on-chip (SoC) designs
- Supports in-system testing and field diagnostics extending product lifecycle
- Facilitates compliance with industry standards and regulations (, )
- Enhances product quality and reliability through comprehensive testing strategies
Designing with DFT principles
- Analyze design for potential testability issues
- Implement scan chain architecture
- Insert scan cells ()
- Connect scan cells to form scan chains
- Add scan enable and
- Incorporate BIST structures
- Integrate test pattern generator ()
- Add response analyzer ()
- Implement for test sequencing
- Apply design rules for improved testability
- Avoid asynchronous logic and gated clocks
- Ensure all flip-flops are controllable and observable
- Implement reset logic for initialization
- Include test modes and multiplexing for test access
- Utilize for DFT insertion and verification (, )
- Perform and optimize design if necessary
- Document testability features and test procedures for manufacturing and field testing
Key Terms to Review (30)
BIST: BIST stands for Built-In Self-Test, a design technique used to facilitate the testing and verification of digital circuits and systems. It integrates testing capabilities directly into the hardware, allowing for automated testing without needing external test equipment. BIST enhances reliability and reduces testing time, making it easier to identify faults during the manufacturing process and throughout the product lifecycle.
BIST Controller: A BIST (Built-In Self-Test) controller is a specialized circuit used in digital systems to enable self-testing of components or systems. It generates test patterns, applies them to the device under test, and evaluates the output to determine if the device is functioning correctly. This approach enhances design for testability by allowing for easier fault detection and diagnosis during manufacturing and in-field operation.
Boundary scan: Boundary scan is a method used in digital design that allows for testing interconnections between integrated circuits (ICs) on a circuit board without the need for physical access to the pins. This technique involves adding a test access port and boundary scan cells to the ICs, enabling efficient testing and diagnosis of faults while minimizing the impact on the design. It is especially valuable in ensuring high reliability and ease of troubleshooting in complex electronic systems.
Built-in self-test: A built-in self-test (BIST) is a mechanism that allows a system to test itself for faults during operation or upon power-up without needing external test equipment. This feature enhances reliability and reduces the time and cost associated with traditional testing methods by integrating testing capabilities directly into the design of the system. By using BIST, designers can improve design for testability, enabling more efficient fault detection and diagnostics.
Design Automation Tools: Design automation tools are software applications that facilitate and streamline the design process in engineering and architecture by automating repetitive tasks and optimizing design workflows. These tools enhance efficiency, accuracy, and productivity, allowing designers to focus on creative aspects while minimizing the risk of human error.
Design for testability: Design for testability is an approach in digital design that enhances the ease and efficiency of testing a system or component. This concept focuses on creating designs that allow for simpler, more effective testing processes, which ultimately leads to higher quality products and reduced development time. By implementing design strategies that facilitate easier access to internal components and signals, engineers can ensure that potential issues are identified and resolved earlier in the development cycle.
DFT: DFT stands for Design for Testability, which is a set of techniques and methodologies used in electronic design to improve the ease with which a circuit can be tested for faults. By integrating testability features into the design phase, DFT helps ensure that devices can be thoroughly tested to confirm they function correctly and meet specifications, ultimately reducing costs and improving reliability.
DO-254: DO-254 is a guidance document that provides a framework for the development of airborne electronic hardware in safety-critical systems. It aims to ensure that the hardware meets the necessary reliability and safety standards, thereby minimizing risks associated with hardware failures in aviation systems. The document emphasizes design for testability, verification processes, and adherence to rigorous development standards, which are essential for certifying hardware in the aerospace industry.
Fault coverage: Fault coverage is a measure of the effectiveness of test patterns in detecting faults in a digital circuit design. It represents the percentage of faults that can be detected by a set of test vectors during testing, which is crucial for ensuring reliability and performance. High fault coverage indicates that most potential faults have been addressed, reducing the likelihood of failures in real-world applications.
Field Diagnostics: Field diagnostics refer to techniques and methods used to identify, analyze, and resolve issues in digital designs directly in the operational environment. This concept is vital for ensuring the reliability and performance of systems, allowing designers and engineers to detect faults or inefficiencies during the testing phase and after deployment. By employing field diagnostics, teams can streamline troubleshooting processes and enhance overall design for testability.
In-system testing: In-system testing refers to the process of verifying and validating the functionality of a digital design while it is still embedded in its operational environment or system. This approach allows for real-time monitoring and assessment of the design's performance, ensuring that it meets specifications under actual working conditions. It plays a crucial role in identifying potential issues that could arise during normal operation, thus enhancing reliability and performance.
Integration testing: Integration testing is a phase in software testing where individual components or systems are combined and tested as a group to identify interface defects and ensure they work together correctly. This type of testing plays a crucial role in verifying that different modules function together as intended, enhancing the reliability of the overall system. It bridges the gap between unit testing, which focuses on individual components, and system testing, which assesses the complete system's behavior.
ISO 26262: ISO 26262 is an international standard for functional safety of electrical and electronic systems in production automobiles, aiming to ensure safety throughout the lifecycle of automotive systems. It provides guidelines for the development process, addressing aspects like risk assessment, validation, and verification to mitigate potential hazards in automotive systems. By implementing ISO 26262, manufacturers enhance reliability and performance while prioritizing safety in vehicle design.
Linear feedback shift register: A linear feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state. It is commonly used in digital circuits for applications such as pseudorandom number generation and error detection, providing a way to generate sequences of bits that appear random. The connection polynomial of the LFSR determines the sequence generated and can be used to design for testability in digital systems by allowing easier testing and fault isolation.
Mentor Graphics FastScan: Mentor Graphics FastScan is a high-performance automatic test pattern generation (ATPG) tool designed for digital circuits. It helps engineers create efficient test patterns that enable the detection of faults within integrated circuits, ensuring that designs are reliable and manufacturable. By improving design for testability, FastScan enhances the ability to diagnose and fix issues early in the design process.
Multiple input signature register: A multiple input signature register (MISR) is a digital circuit used in testing to compactly capture the outputs of a circuit under test and create a unique signature for its behavior. By feeding multiple inputs into the register, it can efficiently generate a single signature that represents the state of the circuit, helping to identify faults and verify functionality during testing processes. This technique enhances design for testability by simplifying the process of checking complex systems.
Multiplexed d flip-flops: Multiplexed d flip-flops are digital storage elements that use a multiplexer to select between multiple input data lines, allowing for the storage of a single bit of information based on a control signal. This design enhances testability by simplifying the circuit layout and reducing the number of individual components needed, making it easier to manage and diagnose faults in digital systems.
On-chip debug: On-chip debug refers to the methods and tools embedded within integrated circuits that allow for the testing, monitoring, and debugging of hardware designs during the development process. This approach enhances design for testability by enabling engineers to observe internal operations, inspect signals, and identify faults without the need for external test equipment. By integrating debug features directly into the chip, designers can streamline the verification process and improve product quality.
Partial Scan: Partial scan is a design technique used in digital circuits to improve testability by selectively connecting a portion of a circuit to scan chains, allowing for easier observation and control of the internal states during testing. This method helps reduce the complexity and area overhead associated with full scan techniques, making it more efficient while still enhancing fault detection capabilities. By implementing partial scan, designers can maintain a balance between test coverage and design resources.
Product Lifecycle Management: Product Lifecycle Management (PLM) is a systematic approach to managing the entire lifecycle of a product from inception, through engineering design and manufacturing, to service and disposal. PLM integrates people, processes, business systems, and information to facilitate the efficient flow of product-related data across all stages, enhancing collaboration and decision-making.
Response Analysis: Response analysis is a method used to evaluate how a digital system reacts to various stimuli or inputs, particularly during the testing phase. This involves assessing performance metrics such as speed, accuracy, and reliability, which helps in identifying potential flaws and optimizing designs for better functionality.
Scan chain design: Scan chain design is a technique used in digital circuits to facilitate testing and debugging by adding extra circuitry that allows the observation and control of internal flip-flops during test operations. This method connects flip-flops in a series, forming a chain that can be easily accessed, which helps in verifying the functionality of the circuit by shifting in test patterns and shifting out response data. This design improves fault detection and simplifies the process of ensuring that digital circuits operate as intended.
Scan enable ports: Scan enable ports are specialized input/output ports used in digital design to facilitate the testing and debugging of integrated circuits. These ports allow for easier access to internal circuit states during testing by enabling the connection of test equipment, which can manipulate and observe the data flow within a digital system. Their primary purpose is to improve design for testability by making it simpler to identify and diagnose faults in the circuitry.
Scan input/output ports: Scan input/output ports refer to the special interfaces on a digital system that allow for the testing and verification of circuit behavior through the application of test vectors. These ports are crucial for enabling automated testing processes, allowing engineers to easily diagnose faults and ensure that the design meets its intended specifications. By integrating scan capabilities, designers can enhance the reliability of digital circuits and simplify the overall testing procedure.
Synopsys Tetramax: Synopsys Tetramax is a software tool used in the electronic design automation (EDA) industry for testing integrated circuits by implementing design-for-testability (DFT) techniques. This tool focuses on enhancing test coverage and reducing test time through optimized test patterns and fault simulation, which are crucial for ensuring that complex digital designs function correctly before production.
Test coverage analysis: Test coverage analysis is a method used to evaluate the extent to which a system's code, requirements, or functionalities are exercised during testing. This process helps identify untested parts of an application, ensuring that all aspects are examined and potential issues are uncovered. It is closely linked to design for testability, as it highlights the importance of creating systems that can be easily tested and verified.
Test pattern generation: Test pattern generation refers to the process of creating specific input sequences or patterns that are used to verify the functionality and performance of digital circuits. This technique is essential for ensuring that the design of a digital system meets its specifications and operates correctly under various conditions. By generating these patterns, designers can identify faults and errors during testing, leading to improved reliability and efficiency in the final product.
Test point insertion: Test point insertion is the practice of adding specific locations within a circuit where test signals can be applied and measured to assess the performance and functionality of that circuit. This technique is crucial in design for testability, as it enables easier fault detection and isolation during manufacturing and testing processes. By strategically placing these test points, designers can facilitate more efficient testing methods, which ultimately enhances reliability and reduces costs.
Test time: Test time refers to the period allocated for evaluating a digital design's functionality and performance after it has been fabricated. This stage is crucial as it involves various testing procedures to identify defects, verify design specifications, and ensure the product meets quality standards. Efficient test time management can significantly reduce costs and improve reliability in digital systems.
Trace capabilities: Trace capabilities refer to the ability of a digital design to monitor and record its internal states and signals during operation, facilitating effective testing and debugging. This feature allows engineers to observe the behavior of a system in real time, which is crucial for identifying faults and ensuring the reliability of the design. By implementing trace capabilities, designers can greatly enhance the testability of their circuits and systems.