Scan Flipflop Input Control for Unknown-Value Capture in Testing

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Solution Overview

Problem

In semiconductor integrated circuits, scan flipflops capturing unknown values during testing complicate failure detection, reducing fault coverage and increasing the number of test patterns required.

Innovation Solution

Incorporating a scan control circuitry that allows scan flipflops to select between data inputs and scan inputs based on operation modes, enabling effective capture of values in capture mode and improving fault detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If scan flipflops capture data from circuit outputs during testing, then test coverage is improved, but unknown values are captured making failure detection difficult

Engineering Contradiction:

Improvefault coverageVSAvoidunknown value capture

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The patent segments the data capture function by providing separate input paths: a data input for capturing circuit outputs and a scan input for capturing known test patterns. The scan flipflop can be selectively connected to either input based on operation mode, preventing unknown value capture while maintaining test coverage.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces scan control circuitry as an intermediary that manages the scan flipflop's input selection. This control circuitry receives control signals and selectively connects the scan flipflop to either the data input or scan input, ensuring that known values are captured during testing rather than unknown circuit outputs.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If scan flipflops capture unknown values, then more test patterns are required, but this increases testing complexity and time

Engineering Contradiction:

Improvefailure detection capabilityVSAvoidnumber of test patterns

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies preliminary action by pre-loading known test patterns through the scan input before capturing circuit outputs. By establishing a known initial state in the scan flipflops, the system can subsequently capture and detect failures more efficiently without requiring additional test patterns to resolve unknown values.

Inventive Principle:

Principle #10Preliminary action

3Loss of information

If scan flipflops are controlled to capture from scan input in capture mode, then unknown value capture is prevented, but additional control circuitry is required

Engineering Contradiction:

Improvedefinitive value captureVSAvoidscan control circuitry

Core Design Contradiction:

Loss of informationVSDevice complexity

Solution Approach 1:

The scan control circuitry is designed with multi-functionality, serving both to select the input source for the scan flipflop and to coordinate the capture and shift operations. This universal control mechanism manages multiple functions within a single circuit block, minimizing the increase in overall device complexity while enabling definitive value capture.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11005458B2Semiconductor integrated circuit adapted to scan testing, and method of designing the same

Publication Date: 2021.05.11 SYNAPTICS INC

AI summary

A semiconductor integrated circuit comprises a scan flipflop comprising a scan input and a data input; and scan control circuitry. The scan control circuitry is configured to control the scan flipflop to capture a value inputted to the scan input in a capture mode.