Matthieu Dubois

Hierarchical parametric test metrics estimation: A ΣΔ converter BIST case study

In this paper we propose a method for evaluating test measurements for complex circuits that are difficult to simulate. The evaluation aims at estimating test metrics, such as parametric test escape and yield loss, with parts per million (ppm) accuracy. To achieve this, the method combines behavioral modeling, density estimation, and regression. The method is demonstrated for a previously proposed Built-In Self-Test (BIST) technique for ΣΔ Analog-to-Digital Converters (ADC) explaining in detail the derivation of a behavioral model that captures the main nonidealities in the circuit. The estimated test metrics are further analyzed in order to uncover trends in a large device sample that explain the source of erroneous test decisions.

Ternary Stimulus for Fully Digital Dynamic Testing of SC S? ADCs

In this paper, a ternary stimulus is proposed for testing ΣΔ Analog-to-Digital Converters (ADCs). The ternary stimulus is composed of three logic levels {-1,0,1} and is obtained by adding a binary stream with a delayed version of itself. Only four switches are added to the input stage of the modulator of the ΣΔ ADC for facilitating the injection of the ternary stimulus. Compared to a binary stimulus, the ternary stimulus contains less quantization noise and allows measuring the SNDR of the ΣΔ ADC for the whole input dynamic range. We discuss the optimization of the ternary stimulus and we demonstrate its efficiency using behavioral simulations of a second-order switched-capacitor (SC) ΣΔ modulator.

Evaluation of digital ternary stimuli for dynamic test of ΣΔ ADCs

Validation of an embedded test technique in terms of its expected yield loss and test escape metrics is a key step before it can be deployed in high-volume manufacturing. However, performing this validation at the design stage usually demands extensive computational resources, which may render electrical simulations infeasible. In this paper, we propose a digital test technique for dynamic test of ΣΔ ADCs based on a digital ternary stimulus together with an advanced simulation framework for its validation. The proposed simulation strategy relies on a combination of transistor-level simulations, behavioural simulations, and statistical tools. To show the feasibility of our approach, we use the proposed validation framework to compare the ternary stimulus with a digital bitstream stimulus, as well as with a standard high-resolution analog sine-wave stimulus.

A Fully-Digital BIST Wrapper Based on Ternary Test Stimuli for the Dynamic Test of a 40 nm CMOS 18-bit Stereo Audio

This paper proposes a fully-digital BIST architecture for the dynamic test of ΣΔ ADCs. The proposed BIST relies on generating a ternary stream that encodes a high-linearity analog sinusoidal and injecting it directly at the input of the ΣΔ modulator. Compared to the well-known bitstream, the use of three logic levels in the ternary stream reduces the quantization noise and, thereby, results in a test with a higher dynamic range that covers the full scale of the ADC. The output response is analyzed on-chip using a simplified version of the sine-wave fitting algorithm to compute the SNDR. A standard SPI bus provides digital external access to the embedded test instruments. The proposed BIST wrapper has been integrated into a 40 nm CMOS 18-bit stereo audio ΣΔ ADC IP core provided by ST Microelectronics. It incurs an overall area overhead of 7.1% and the total test time is 28 ms per channel. Experimental results on fabricated chips demonstrate an excellent correlation between the BIST and the standard functional specification test.

\Sigma\Delta

Digital techniques for an embedded dynamic test of \(\varSigma \varDelta \) ADCs have been recently presented in the literature. These techniques are based on the use of \(\varSigma \varDelta \) streams for the stimulation of the ADC. Binary and ternary test stimuli have been proposed. In this chapter, we aim at the validation of these embedded test techniques, comparing the results obtained with the different types of digital stimuli with a standard high-resolution analog sinusoidal stimulus. This validation is done in terms of the expected yield loss and test escapes of the proposed embedded techniques. However, performing this validation at the design stage demands extensive computational resources, which may render electrical simulations infeasible. Thus, we propose an advanced simulation framework for this validation. The proposed simulation strategy relies on a combination of transistor-level simulations, behavioral simulations, and statistical tools.

ADC

The aim of this work is to understand the evolutions of the β1 metastable austenite phase of a CuAlBe Shape Memory Alloy at macroscopic and microscopic scales under mechanical solicitation by neutron diffraction. The tensile specimen, taken in the raw material is subjected to superelastic cycles at room temperature on SMARTS diffractometer. Before loading, the mater ial is fully austenitic. During loading, after elastic deformation of austenite, phase transformation starts, martensite variants appear. The material follows a law of pseudo elastic behavior. At the end of the first mechanical cycle after unloading, the macroscopic curve does not fully return into its original point. A macroscopic deformation is observed. The evolution of first order microdeformations during mechanical cycles shows a large deformation of {400} plane family. This deformation is linked to the presence of <001> partial fibber characterizing the crystallographic texture of the material after elaboration. The FWHM of the (400) diffraction peak is also largely increased during loading. This increase is the signature of the generation of stacking faults during the transformation of β1 metastable austenite into β1 martensite.

Statistical Evaluation of Digital Techniques for \varSigma \varDelta ADC BIST

This work aims to study by neutron diffraction the evolution of metastable phases of CuAlBe shape memory alloy after plastic deformation. Two samples were studied: the first one deformed by cold rolling at a reduction rate of 15% and the second, deformed by cold rolling at 15% followed by hot rolling at 200°C for a reduction rate of 30% respectively. Before plastic deformation, the material is fully austenitic at ambient temperature. Its crystallographic texture is mainly characterized by a <001> partial fibber. After deformation, this partial fibber disappears and the crystallographic texture is composed by isolated orientations. At higher reduction rates, the texture of austenitic phase remaining in the material is characterized by a <111> fibber. The rolling process modifies metastable phase quantities. After deformation at a reduction rate of 15%, the volume fraction of metastable austenite remaining is close to 8%. Plastic deformation also greatly modifies the characteristic transformation temperatures and enlarges the hysteresis. The material plastically deformed after hot rolling presents large variations of intensities of diffraction peaks belonging to martensite phase during a thermal cycle at low temperature. This effect is attributed to a reorganization of variants due to an evolution of crystallographic texture of martensite.

Study of Superelastic Behavior of CuAlBe Shape Memory Alloy by Neutron Diffraction

This work presents the texture evolution of the austenitic phase of a copper based shape memory alloy by neutron diffraction. The Cu-11%Al-0.62%Be (in mass %) alloy was subjected to cold and hot rolling processes. The texture of the rolled samples at reduction rates of 5%, 10% and 15% respectively were compared to those of the raw material. A <001> partial fiber is observed for the raw material and cold rolled samples whereas the texture of the hot rolled sample is mainly characterized by a <111> fiber. The influence of these mechanical treatments on the transition temperatures and the hysteresis evolution was also analysed by following the integrated intensity of the {220} reflection of the austenitic phase. A shift towards low temperatures of martensitic transition temperatures is observed with the increasing of the rolling rate.

Study of the Influence of Plastic Deformation on Metastable Phases of CuAlBe Shape Memory Alloy by Neutron Diffraction

This work was devoted to the study of a copper based shape memory alloy using the neutron diffraction method. We present the crystallographic texture evolution of the austenite phase of the Cu-11%Al-0.62%Be (wt. %) alloy which was subjected to cold and hot rolling processes. The texture of the cold rolled samples at reduction rates of 5%, 10% and 15% respectively was measured and compared to the raw material. A <001> partial fiber is observed for the raw material and for cold rolled samples whereas the texture of the hot rolled sample is mainly characterized by a <111> fiber. On the second part, we have studied the influence of the rolling treatment on the transition temperatures by following the integrated intensity of the {220} austenite reflection. The increase of the rolling rate seems to shift the characteristic temperatures towards low temperatures.

Neutron Diffraction Study of a CuAlBe Shape Memory Alloy

In the present study, the evaluation of the deformation and the determination of the first order residual stresses in shot peened aluminium plate have been performed by neutron diffraction on the strain imaging instrument SALSA at the Institut Laue Langevin, Grenoble, France, in order to validate a model of finite element analysis permitting to predict the final deformation. The sample used in this study is a rolled aluminium sheet (Al 2024 T3 alloy) which was clamped in a steel frame and peened following exactly the industrial production process. The first measurements were performed on the sample while it was still clamped. The second set was made after removing it from the frame. For each case, we measured the lattice strains and determined the stress repartition in the three principal directions.