Bidirectional Scan Cells for Reduced Silicon Overhead

Solution Overview

Problem

Conventional scan chain diagnosis methods face challenges in accurately diagnosing un-modeled faults in logic test chips, particularly intermittent faulty behaviors, which degrades diagnostic accuracy and resolution, and often require additional hardware or complex software algorithms.

Innovation Solution

The implementation of bidirectional scan chains with tri-state buffers and multiplexers allows for shift operations in both directions based on a control signal, reducing silicon area overhead and routing congestion, enabling more effective fault detection and diagnosis without the need for extra hardware.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If bidirectional scan chains are implemented using conventional methods with separate forward and backward paths, then diagnostic accuracy is improved, but silicon area overhead and routing congestion increase

Engineering Contradiction:

Improvediagnostic accuracyVSAvoidsilicon area overhead

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent merges the forward and backward scan paths into a single shared physical path. The same scan chain infrastructure is used for both directions by controlling the direction of data flow through tri-state buffers, eliminating the need for separate forward and backward path hardware and reducing silicon area overhead.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces dynamic control mechanisms (tri-state buffers and multiplexers) that allow the scan chain to switch between forward and backward operation modes. This dynamic reconfiguration enables a single static physical structure to perform multiple directional functions, reducing hardware overhead while maintaining diagnostic accuracy.

Inventive Principle:

Principle #15Dynamics

2Measurement precision

If bidirectional scan chains are implemented using conventional methods with separate forward and backward paths, then diagnostic accuracy is improved, but routing congestion increases

Engineering Contradiction:

Improvediagnostic accuracyVSAvoidrouting congestion

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges the forward and backward scan paths into a single shared physical path. The same scan chain infrastructure is used for both directions by controlling the direction of data flow through tri-state buffers, eliminating the need for separate forward and backward path hardware and reducing silicon area overhead.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces dynamic control mechanisms (tri-state buffers and multiplexers) that allow the scan chain to switch between forward and backward operation modes. This dynamic reconfiguration enables a single static physical structure to perform multiple directional functions, reducing hardware overhead while maintaining diagnostic accuracy.

Inventive Principle:

Principle #15Dynamics

3Device complexity

If conventional scan chain diagnosis methods are used, then hardware complexity is reduced, but diagnostic accuracy for un-modeled faults degrades

Engineering Contradiction:

Improvehardware complexityVSAvoiddiagnostic accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent introduces dynamic control mechanisms (tri-state buffers and multiplexers) that allow the scan chain to switch between forward and backward operation modes. This dynamic reconfiguration enables a single static physical structure to perform multiple directional functions, reducing hardware overhead while maintaining diagnostic accuracy.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The bidirectional scan chain structure enables the system to perform its own diagnosis by shifting test patterns in both directions and comparing results, eliminating the need for external physical failure analysis instruments and providing self-diagnostic capability for detecting intermittent and un-modeled faults.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS11408938B2Bidirectional scan cells for single-path reversible scan chains

Publication Date: 2022.08.09 SIEMENS INDUSTRY SOFTWARE INC

AI summary

A circuit comprises a plurality of scan chains. The plurality of scan chains comprises bidirectional scan cells. Each of the bidirectional scan cells comprises two serial input-output ports serving as either a serial data input port or a serial data output port based on a control signal. Each of the plurality of scan chains is configured to perform a shift operation in either a first direction or a second direction based on the control signal. The first direction is opposite to the second direction.