Local Capture Clock Generation for Accurate Scan Testing
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Solution Overview
Problem
Existing scan testing methods face inaccuracies due to distortions and phase delays in capture pulses caused by transmission line effects and power supply transients, leading to unreliable test results, especially in large systems with high-frequency clocks.
Innovation Solution
The system divides the electronic system into blocks with separate power supply traces and uses a Capture Clock Generator with shadow registers to stabilize the Clock Distribution Network and generate non-overlapping capture pulses, ensuring accurate timing and reducing power supply transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the clock distribution network is deactivated during capture mode, then power consumption is reduced, but the capture pulses become distorted due to transmission line effects and power supply transients
Solution Approach 1:
The clock distribution network is kept active and stabilized before capture mode begins. Functional clock pulses are applied to the circuit under test prior to capturing, ensuring the clock network is fully charged and stable. This preliminary action prevents transmission line effects and power supply transients from distorting the capture pulses, while still allowing power reduction during non-capture periods through selective clock gating.
2Productivity
If capture pulses are generated without stabilizing the clock distribution network first, then testing speed is improved, but timing accuracy deteriorates due to transmission line effects
Solution Approach 1:
Before generating capture pulses, the system performs a stabilization phase where functional clock pulses are applied to the clock distribution network. This ensures all transmission lines are charged and stable before the actual capture operation, eliminating timing errors caused by transient effects while maintaining high-speed testing capability.
Solution Approach 2:
The system uses periodic functional clock pulses to stabilize the clock distribution network before capture. By applying regular clock cycles, the network reaches a steady state with predictable timing characteristics, ensuring accurate capture pulse timing without sacrificing overall test speed.
3Reliability
If the clock distribution network is always active, then capture pulse distortion is eliminated, but power consumption increases
Solution Approach 1:
The clock distribution network is activated and stabilized in advance before capture mode begins, then can be selectively gated off during non-capture periods. This approach ensures capture pulse accuracy when needed while reducing overall power consumption by keeping the network inactive during scan-in and scan-out operations.
Solution Approach 2:
The system dynamically controls the clock distribution network, switching between active and inactive states based on the test phase. During capture mode, the network is active and stabilized; during other phases, it can be gated off. This dynamic control maintains capture pulse accuracy while optimizing power consumption throughout the test cycle.
Data Source
AI summary
An electronic system is configured for scan testing, with a clock distribution network going to a plurality of blocks of the system, and a test capture clock being generated locally at each block. Capture clock pulses may optionally be generated at different times for different blocks, and may optionally be suppressed for some blocks.