Experimental Validation of Predictive Oscillation Based Test J. Font, E. Isern, M. Roca, R. Picos, E. García!Moreno Electronic Technology Group, Physics Department, University of Balearic Islands, Palma de Mallorca, 07122, SPAIN e!mail: joan.font@uib.es — ! "# $ %$ " & # ’ $ %$ # ($ & %$ %$ $ # ’ $ $ %$# I. INTRODUCTION The difficulties to access the internal nodes and the price of the automatic test equipment (ATE) to test the performance parameters of integrated circuits (IC) have opened the door to innovative and alternative test solutions such as the OBT technique and the Predictive Test approach. Analogue integrated circuits are very sensitive to process variations. It means that, though preserving the layout integrity, the fulfilment of the circuit specifications is not often guaranteed. That is why parametrical test is necessary. Oscillation Based Test (OBT) consists in converting the circuit under test (CUT) into an oscillator during the test mode by adding an external feedback network [1]. The structural (hard) defects, or the process variations (soft defects), will cause the frequency and the amplitude of the oscillation in the faulty circuit to change compared to those of the fault!free circuit. The advantages of this technique are its simplicity, its robustness and the elimination of the test vector generation. Recently the OBT strategy has been applied to performance prediction. Instead of measuring directly the performance parameters of the CUT they can be predicted from the test observables in test mode (OBT) by using statistical tools [2, 3]. Up to now the combination of the OBT strategy and test prediction, known as Predictive Oscillation Based Test (POBT), had led to encouraging results. It has been proved the efficiency of this methodology focused on a biquad filter composed of two OTAs [4]. By simulation through HSPICE and Monte Carlo analysis it was demonstrated the high correlation between the filter parameters and the test observables. In this paper, on the contrary, we validate experimentally the POBT technique by applying it to a set of samples of commercial OpAmps from different manufacturers. It is important to remark that here we do not deal only with encouraging simulation results but with experimental results. The POBT strategy has been applied to commercial Integrated Circuits like the well!known TL071 operational amplifiers. The experimental measurements have been made in test mode and when the CUT works in normal operation as a filter. The paper is organized in six sections. After this introduction, Section 2 presents an overview of the predictive test strategy combined with the oscillation based test. Section 3 describes the CUT performance in normal operation. Section 4 describes the test mode operation. In section 5 the experimental results in terms of their prediction accuracies of some parameters are evaluated. Section 6 shows the simulation results verifying the above experimental results. Finally, Section 7 provides the main conclusions and future work to do. II. PREDICTIVE OSCILLATION BASED TEST OVERVIEW Predictive Test [2,3] is intended to predict some performance parameters of the CUT by measuring some selected observables when it is configured in test mode. That way, performance parameter estimation can be done faster and without using costly external stimuli generators. The technique we use to make the CUT working in test mode is the well!known strategy of the Oscillation Based Test (OBT) [1,2]. That is the reason why the combination of Predictive Test and OBT is called Predictive Oscillation Based Test (POBT). Oscillation Based Test (OBT) consists of adding an external circuitry to the circuit under test (CUT) to