Sequential Decompressor Overscanning for Test Compression Efficiency
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Solution Overview
Problem
Existing test compression methods, such as XOR decompressors, are inefficient as they are restricted to using only scan data available in the same scan cycle, leading to unused data and the need for additional hardware or control pins to load variables into the PRPG during the ATPG process.
Innovation Solution
Implementing a sequential decompressor system that overscans for additional cycles to bring in variables into the PRPG, allowing reuse of scan data across multiple slices and eliminating the need for additional hardware or control pins by clocking the PRPG and scan channels simultaneously.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If XOR decompressors are used for test compression, then test data volume is reduced, but scan data from sparse slices cannot be reused in dense slices leading to inefficiency
Solution Approach 1:
The patent transitions from static XOR decompressors that operate slice-by-slice to a dynamic sequential decompressor that processes the entire test pattern across multiple scan cycles. The decompressor dynamically adapts its operation by loading care bits from sparse slices during early cycles and reusing them in later cycles when solving dense slices, maximizing data utilization efficiency.
Solution Approach 2:
The sequential decompressor maintains continuous useful action by keeping the scan engine running throughout the entire test pattern generation process. Instead of pausing between slices, the system continuously shifts scan data through the decompressor, allowing care bits to be propagated and reused across multiple slices without idle time, thereby eliminating data waste.
2Productivity
If sequential decompressor loads scan input variables into PRPG during early cycles, then all care bits can be solved, but additional hardware or control pins are required to freeze scan channels
Solution Approach 1:
The patent merges the operation of the PRPG loading process with the normal scan channel clocking. Instead of freezing scan channels to load variables, the system combines variable loading with continuous scan operation by using the same clock signal for both PRPG updates and scan channel shifting, eliminating the need for separate control mechanisms.
Solution Approach 2:
The sequential decompressor performs self-service by automatically managing the loading and propagation of care bits through the scan engine without requiring external control pins. The system uses its own internal state and the natural flow of scan data to determine when and how to load variables, making the process autonomous and hardware-efficient.
3Ease of manufacture
If XOR decompressor uses only same-cycle scan data, then implementation is simple, but care bits in sparse slices cannot be utilized for dense slices
Solution Approach 1:
The patent adds a temporal dimension to the decompression process by extending it across multiple scan cycles rather than confining it to a single cycle. This dimensional expansion allows scan data to flow through time, enabling care bits from early cycles to be reused in later cycles, thereby converting unused data into valuable test information without complicating the basic XOR logic.
Data Source
AI summary
Systems and methods efficiently bring additional variables into a Pseudo-Random Pattern Generator (“PRPG”) in the early cycles of an automatic test pattern generation (“ATPG”) process without utilizing any additional hardware or control pins. Overscanning (e.g., scanning longer than the length of the longest channel) for some additional cycles brings in enough variables into the PRPG. Data corresponding to earlier cycles of the ATPG process is removed.