BIST methodology for low-cost parametric timing measurement of high-speed source synchronous interfaces
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With the scaling of technology nodes, the speed performance of microprocessors has rapidly improved but the scaling of off-chip input/output (I/O) bandwidth is limited by physical pin resources and interconnect technologies. In order to reduce the performance gaps, new interface techniques have emerged and the marketplace has moved towards higher levels of integration with system on a chip (SoC) implementations. The advent of new techniques, however, has led to new challenges on the semiconductor and automated test equipment (ATE) industries. The relatively slow growing ATE technology comparing to I/O speeds especially intensifies manufacturing test issues. Testing high speed I/O timing parameters requires expensive high performance test equipment with high accuracy and resolution. The requirements increase integrated circuit (IC) manufacturing costs and thus test issues have become critical. This thesis focuses on on-chip test methods to improve test accuracy and reduce test costs for high speed double data rate (DDR) memory I/Os using source synchronous clocking. For testing the I/O timing parameters, a phase interpolator based on-chip timing sampler using a cycle-by-cycle control method was developed. This circuit generates data and clock patterns and controls the time delay between data and clock to detect the timing mismatch which indicates timing degradations. The on-chip timing sampler was implemented as a built-in self test (BIST) circuit for low-cost parametric timing measurements. The BIST scheme was fabricated with a 0.18-um CMOS process technology. Using the static and dynamic modes, measurement results are obtained for the I/O timing parameters such as the setup and hold times, input voltage-level variations tolerances, duty distortion tolerances and data skews. Moreover, a delay mismatch measurement method was developed to improve measurement accuracy using a simple control circuit. This delay mismatch detector measures timing mismatches between data and clock paths and then the timing mismatches are converted to timing specifications. This scheme is also implemented along with analog to digital converter (ADC) to collect digital test results supporting low-cost system-level tests. Thus, the low-frequency test results show that our on-chip measurement techniques provide an attractive low-cost solution and is effectively applied for testing high speed source synchronous systems.