Scan-Chain Flip-Flops Using Functional Registers as Test Points

Solution Overview

Problem

Existing scan testing methods for large gate count devices face challenges in achieving high scan test coverage while minimizing circuit overhead, routing congestion, and power consumption, particularly due to the addition of dedicated test flip-flops and test point insertion.

Innovation Solution

Repurpose existing functional shift registers and standalone flip-flops in the device to insert test points for controlling and observing circuit nodes during scan testing, reducing the need for additional dedicated test flip-flops and minimizing circuit overhead and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If dedicated test flip-flops are added to improve scan test coverage, then test coverage is improved, but circuit overhead and area increase

Engineering Contradiction:

Improvescan test coverageVSAvoidcircuit overhead

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent makes existing functional flip-flops serve dual purposes: their primary functional role in the circuit and their secondary role as test points for scan testing. By configuring existing flip-flops to output values received at their scan-in inputs during scan testing, the invention eliminates the need for separate dedicated test flip-flops, thereby improving scan test coverage without increasing circuit area.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Productivity

If dedicated test flip-flops are added to reduce test time, then productivity is improved, but device complexity increases

Engineering Contradiction:

Improvetest timeVSAvoidcircuit complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The invention enables existing functional flip-flops to serve themselves as test points by configuring them to output values received at their scan-in inputs during scan testing. This self-service approach eliminates the need for additional dedicated test circuitry, thereby reducing device complexity while maintaining improved test coverage and reduced test time.

Inventive Principle:

Principle #25Self-service

3Reliability

If test point insertion is used to improve controllability and observability, then scan test coverage is improved, but power consumption increases

Engineering Contradiction:

Improvescan test coverageVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by stationary object

Solution Approach 1:

The patent makes existing functional flip-flops serve dual purposes: their primary functional role in the circuit and their secondary role as test points for scan testing. By configuring existing flip-flops to output values received at their scan-in inputs during scan testing, the invention eliminates the need for separate dedicated test flip-flops, thereby improving scan test coverage without increasing circuit area.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20260036623A1Flip-flops for circuit testing based on scan chains

Publication Date: 2026.02.05 TEXAS INSTRUMENTS INC

AI summary

An example device described herein includes first functional circuitry, second functional circuitry, and a shift register coupled to the first functional circuitry. The shift register of the example device includes a flip-flop, the flip-flop including a scan-in input coupled to the second functional circuitry, a scan-enable input, and an output. The example device also includes first test circuitry coupled to the scan-enable input and configured to cause the flip-flop to output a first value received by the flip-flop at the scan-in input from the second functional circuitry.