Multi-Core IC Scan Testing with Shared TDI and TDO Pads
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Solution Overview
Problem
Multi-core integrated circuits require a large number of test pads for scan testing, which increases the number of external pins and prolongs test time, especially when testing multiple cores simultaneously.
Innovation Solution
Implementing common scan test data input and output pads for all cores, allowing simultaneous parallel testing of nominally similar cores, reducing the number of test pads required and enabling efficient diagnosis of defective cores by combining test response signals for comparison with expected responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If separate TDI and TDO pads are provided for each scan chain in each core, then diagnostic capability is improved, but the number of external pins increases
Solution Approach 1:
The patent combines multiple TDO signals from different cores and scan chains into a single shared TDO pad. Specifically, response signals from multiple scan chains are multiplexed and combined through logic circuits (OR gates, multiplexers) before being output through a common TDO pad, thereby reducing the number of external pins required while maintaining the ability to diagnose defects in individual cores
Solution Approach 2:
The shared TDO pad serves multiple functions by receiving and outputting test response signals from multiple different scan chains and cores. The pad is universally used for diagnosing defects across all cores, eliminating the need for dedicated TDO pads for each core while preserving diagnostic capabilities through intelligent signal combining
2Productivity
If common TDI pads are used for all cores with simultaneous parallel testing, then test time is reduced, but the number of TDO pads must still be m*(n+1)
Solution Approach 1:
The patent merges multiple TDO pads into a single shared TDO pad by combining response signals from multiple scan chains using logic circuits. This allows all cores to be tested in parallel using common TDI pads while also using a common TDO pad, thereby reducing both test time and the number of external pins required
3Difficulty of detecting and measuring
If separate TDI and TDO pads are provided for each core, then testing of each core can be performed independently, but test time is multiplied by the number of cores
Solution Approach 1:
The patent combines TDO output signals from multiple cores through logic circuits and multiplexers, enabling parallel testing of multiple cores through shared TDI and TDO pads. This maintains the ability to independently diagnose each core while reducing total test time by testing all cores simultaneously rather than sequentially
Data Source
AI summary
Testing an integrated circuit (IC) that has a set of nominally similar cores and pairs of test data input (TDI) and test data output (TDO) pads common to the different cores. Similar scan chains in parallel in the different cores provide response signals as functions of corresponding TDI signals. Respective combined TDO signals are provided to the TDO pads. In the absence of a defect, the combined TDO signals are asserted and de-asserted like the response signals from corresponding chains in the different cores and like corresponding expected response signals. The combined TDO signals are different from the corresponding expected response signals in the presence of a defect in at least one of the cores. If the result is a fail, the ATE may identify a defective core using a diagnosis module in the IC providing response signals from a selected core.