Optimal testing of VLSI analog circuits

Abstract
The high cost of capital equipment for production testing coupled with the time that an analog circuit spends on a tester has made it imperative to minimize average chip testing time during production. Testing time can be reduced by decreasing the number of tests that need to be performed on a circuit and by optimizing the order of the tests. This can be done by studying performance data for a sample of chips or using simulation data. The advantage of simulation data is that a large number of circuits do not have to be nonoptimally tested in order to generate the data set. Generating simulation data for very large scale integration (VLSI) analog circuits has been considered to be very difficult because of the computational cost of simulating a large system, the very large number of random variables needed to model the manufacturing process, and the need to model and simulate not only random parameter variations but also spot defects. These problems are overcome by decomposing a circuit into several blocks, which are linked together by a behavioral model of the system. In order for this to work, the blocks must not depend on a large set of significant random variables, and the blocks should not be tightly coupled. In this paper we demonstrate our statistical simulation methodology for a VLSI analog circuit. The proposed approach to defect simulation is applied to a parallel filter bank which has a total of 32 channels, is composed of 67 blocks, and has over 4040 transistors and 750 capacitors. Simulation results are used to optimize the test set for this circuit, by showing that the frequency response tests at many frequencies are redundant.

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