Date of Degree
PhD (Doctor of Philosophy)
Electrical and Computer Engineering
Sudhakar M. Reddy
With the ever increasing integration capability of semiconductor technology, today's large integrated circuits require an increasing amount of data to test them which increases test time and elevated requirements of tester memory.
At the same time, as VLSI design sizes and their operating frequencies continue to increase, timing-related defects are high proportion of the total chip defects and at-speed test is crucial. DFT techniques are widely used in order to improve the testability of a design. While DFT techniques facilitate generation and application of tests, they may cause the test vectors to contain non-functional states which result in higher switching activities compared to the functional mode of operation. Excessive switching activity causes higher power dissipation as well as higher peak supply currents. Excessive power dissipation may cause hot spots that could cause damage the circuit. Excessive peak supply currents may cause higher IR drops which increase signal propagation delays during test causing yield loss.
Several methods have been proposed to reduce the switching activity in the circuit under test during shift and capture cycles. While these methods reduce switching activity during test and eliminate the abnormal IR drop, circuits may now operate faster on the tester than they would in the actual system. For speed related and high resistance defect mechanisms, this type of undertesting means that the device could be rejected by the systems integrator or by the end consumer and thus increasing the DPPM of the devices. Therefore, it is critical to ensure that the peak switching activity generated during the two functional clock cycles of an at-speed test is as close as possible to the functional switching activity levels specified for the device.
The first part of this dissertation proposes a new method to generate test vectors that mimic functional operation from the switching activity point of view. It uses states obtained by applying a number of functional clock cycles starting from the scan-in state of a test vector to fill unspecified scan cells in test cubes. Experimental results indicate that for industrial designs, the proposed techniques can reduce the peak capture switching on average by 49% while keeping the quality of test very close to conventional ATPG.
The second part of this dissertation addresses IR-drop and power minimization techniques in embedded deterministic test environment. The proposed technique employs a controller that allows a given scan chain to be driven by either the decompressor or pseudo functional background. Experimental results indicate an average of 36% reduction in peak switching activity during capture using the proposed technique.
In the last part of this dissertation, a new low power test data compression scheme using clock gater circuitry is proposed to simultaneously reduce test data volume and test power by enabling only a subset of the scan chains in each test phase. Since, most of the total power during test is typically in clock tree, by disabling significant portion of clock tree in each test phase, significant reduction in the test power in both combinational logic and clock distribution network are achieved. Using this technique, transitions in the scan chains during both loading of test stimuli and unloading of test responses decrease which will permit increased scan shift frequency and also increase in the number of cores that can be tested in parallel in multi-core designs. The proposed method has the ability of decreasing, in a power aware fashion, the test data volume. Experimental results presented for industrial designs demonstrate that on average reduction factors of 2 and 4 in test data volume and test power are achievable, respectively.
Copyright 2011 Elham khayat moghaddam
Khayat Moghaddam, Elham. "On low power test and low power compression techniques." doctoral dissertation, University of Iowa, 2011.