Extended Scan Flip-Flops for High-Coverage Circuit Testing

Solution Overview

Problem

Integrated circuits, such as microcontrollers, require high test coverage but adding additional flip-flops for observation points increases cost and chip size, making it undesirable.

Innovation Solution

Implementing extended scan flip-flops with additional input circuitry to function as both input wrapper cells and observation points, reducing the need for dedicated observation points and minimizing chip area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If additional flip-flops are added to implement observation points for high test coverage, then test coverage is improved, but chip cost and size increase

Engineering Contradiction:

Improvetest coverageVSAvoidchip area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The scan flip-flops are designed to perform dual functions: serving as input wrapper cells during normal operation and as observation points during testing. The test input circuit includes a multiplexer that can switch between receiving data from the preceding flip-flop in the sequence or from a test result signal, enabling the same hardware to support both operational and testing requirements without adding dedicated observation point flip-flops.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If additional flip-flops are added to implement observation points for high test coverage, then test coverage is improved, but chip cost increases

Engineering Contradiction:

Improvetest coverageVSAvoidchip cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The scan flip-flops are designed to perform dual functions: serving as input wrapper cells during normal operation and as observation points during testing. The test input circuit includes a multiplexer that can switch between receiving data from the preceding flip-flop in the sequence or from a test result signal, enabling the same hardware to support both operational and testing requirements without adding dedicated observation point flip-flops.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Area of stationary object

If scan flip-flops are extended with additional input circuitry to function as both input wrapper cells and observation points, then chip area is reduced, but device complexity increases

Engineering Contradiction:

Improvechip areaVSAvoidflip-flop structure

Core Design Contradiction:

Area of stationary objectVSDevice complexity

Solution Approach 1:

A test input circuit is introduced as an intermediary component between the sequential input wrapper scan flip-flops and the test result output. This circuit includes a multiplexer that mediates the signal flow by selecting whether to capture data from the preceding flip-flop or from the test result signal, thereby managing the added complexity in a controlled manner while achieving the goal of reduced chip area.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12449472B2Circuit and method for testing a circuit

Publication Date: 2025.10.21 INFINEON TECHNOLOGIES AG

AI summary

According to various embodiments, a circuit is described including a plurality of scan flip-flops including a sequence of input wrapper scan flip-flops and including, for each input wrapper scan flip-flop of at least a subset of the input wrapper scan flip-flops, at the input wrapper scan flip-flop's test input a respective test input circuit configured to, when supplied with a mode control signal having a first value, connect the test input to the output of the preceding input wrapper scan flip-flop such that the test input of the flip-flop is supplied with the content of the preceding input wrapper scan flip-flop and when supplied with the mode control signal having a second value, connect the test input to an output of a part of the circuit such that the test input of the flip-flop is supplied with a value depending on a test result.