Louay Abdallah

Sensors for built-in alternate RF test

The paper discusses a variety of sensors to enable a built-in test in RF devices. The list of sensors includes dummy circuits, process control monitors, DC probes, an envelope detector, and a current sensor. Dummy circuits and process control monitors are simple circuits that do not tap into the signal path of the RF device. Instead, they monitor the device by virtue of being subject to the same process variations. Their outputs form an alternative measurement pattern which can be mapped to the performances of the device using a typical alternate test flow. The rest of the sensors are physically connected to the RF device, thus they can detect random catastrophic defects within it and, as an auxiliary benefit, they can improve the accuracy in predicting its performances. The degradation that these sensors incur is carefully assessed and the RF device is co-designed with them to correct for the losses. The operation and test efficiency of the sensors is demonstrated for the case of an RF LNA using post-layout simulations.

Defect-oriented non-intrusive RF test using on-chip temperature sensors

We present a built-in, defect-oriented test approach for RF circuits that is based on thermal monitoring. A defect will change the power dissipation of the circuit under test from its expected range of values which, in turn, will induce a change in the expected temperature in the substrate near the circuit. Thus, an on-chip temperature sensor that monitors the temperature near the circuit can reveal the existence of the defect. This test approach has the key advantage of being non-intrusive and transparent to the design since the temperature sensor is not electrically connected to the circuit. We discuss the basics of thermal monitoring, the design of the temperature sensor, as well as the test scheme. The technique is demonstrated on fabricated chips where a temperature sensor is employed to monitor an RF low noise amplifier.

Experiences with non-intrusive sensors for RF built-in test

This paper discusses a new type of sensors to enable a built-in test in RF circuits. The proposed sensors provide DC or low-frequency measurements, thus they can reduce drastically the testing cost. Their key characteristic is that they are nonintrusive, e.g. they are not connected electrically to the RF circuit. Thus, the performances of the RF circuit are unaffected by the monitoring operation. The sensors function as process monitors and share the same environment with the RF circuit. The underlying principle is that the sensors and the RF circuit are subject to the same process variations, thus shifts in the performances of the RF circuit can be inferred implicitly by shifts in the outputs of the sensors. We present experimental results on fabricated samples that include an LNA with embedded sensors. The samples are collected from different sites of a wafer such that they exhibit process variations. We demonstrate that the performances of the RF circuit can be predicted with sufficient accuracy through the sensors by employing the alternate test paradigm.

RF Front-End Test Using Built-in Sensors

This article proposes a new class of sensors for built-in test in RF devices. These sensors are placed in close proximity to the DUT on the same substrate without being electrically connected to it. Instead, they monitor it by virtue of being subjected to the same process variations. The authors also describe other types of sensors they have studied, including DC probes, an envelope detector, and a current sensor.

Testing RF circuits with true non-intrusive built-in sensors

We present a set of sensors that enable a built-in test in RF circuits. The key characteristic of these sensors is that they are non-intrusive, that is, they are not electrically connected to the RF circuit, and, thereby, they do not degrade its performances. In particular, the presence of spot defects is detected by a temperature sensor, whereas the performances of the RF circuit in the presence of process variations are implicitly predicted by process sensors, namely dummy circuits and process control monitors. We discuss the principle of operation of these sensors, their design, as well as the test strategy that we have implemented. The idea is demonstrated on an RF low noise amplifier using post-layout simulations.

Fast deployment of alternate analog test using Bayesian model fusion

In this paper, we address the problem of limited training sets for learning the regression functions in alternate analog test. Typically, a large volume of real data needs to be collected from different wafers and lots over a long period of time to be able to train the regression functions with accuracy across the whole design space and apply alternate test with high confidence. To avoid this delay and achieve a fast deployment of alternate test, we propose to use the Bayesian model fusion technique that leverages prior knowledge from simulation data and fuses this information with data from few real circuits to draw accurate regression functions across the whole design space. The technique is demonstrated for an alternate test designed for RF low noise amplifiers.

Multivariate statistical techniques for analog parametric test metrics estimation

The high cost for testing the analog blocks of a modern chip has sparked research efforts to replace the standard tests with less costly alternative tests. However, test engineers are rather reluctant to adopt alternative tests unless they are evaluated thoroughly before moving to production and they are proven to maintain test quality. This paper gives a comprehensive overview of statistical techniques based on density estimation for evaluating analog parametric test metrics during the test development phase. A large-scale simulation study is carried out for the first time with the aim to demonstrate these techniques in action.

Accurate estimation of analog test metrics with extreme circuits

Specification-based testing of analog/RF circuits is very costly due to lengthy test times and highly sophisticated test equipment. Alternative test measures, extracted by means of Built-In Test (BIT) techniques, are a promising approach to replace standard specification-based tests. However, these test measures must be evaluated at the design stage, before the real production, by estimating parametric test errors such as Test Escapes (TE) and Yield Loss (YL). An accurate estimation of these metrics requires a large non-biased sample of circuit instances including parametric defective ones. Since these extreme circuits are rare events, they cannot be obtained with a Monte Carlo simulation of an affordable size. However, statistical learning techniques, in combination with Monte Carlo simulation, can allow the generation of such a sample for multivariate test metrics estimation. In this paper, we will demonstrate this technique for the evaluation of an RF LNA BIT technique for which a large database of 106 circuits has been simulated for comparison purposes.

Adaptive logical control of RF LNA performances for efficient energy consumption

This paper presents a new approach for controlling power consumption in RF devices. The approach is based on the definition of application-dependent performance modes for power hungry RF circuits and a logical control strategy that adjusts the power supply of each circuit to the mode required by the application. The control strategy uses embedded sensors, a recursive parameter identification approach and regression models for performance prediction, while demanding minimum embedded resources for computation. The control strategy is robust with respect to circuit parametric deviations due to the manufacturing process or ageing mechanisms. The strategy is illustrated for the case of an RF LNA using envelope detectors as embedded sensors. Simulation results of the control strategy at the transistor-level illustrate the energy savings that can be obtained for an example application.

True non-intrusive sensors for RF built-in test

In this summary paper, we discuss two types of sensors that provide a built-in test solution for RF circuits. The key characteristic of the sensors is that they are non-intrusive, in the sense that they are not electrically connected to the RF circuit under test. This has the important advantage that the design of the RF circuit becomes totally independent from the design of the sensors. In other words, the RF circuit design methodology and performance trade-offs are totally transparent to the insertion of the built-in test strategy. In particular, we propose variation-aware sensors to implement an implicit functional test and a temperature sensor to implement a defect-oriented test. The proposed sensors provide DC or low-frequency measurements, thus they have the potential to reduce drastically the test cost. We discuss the principle of operation of the sensors, we provide design guidelines, and we demonstrate the concept on a set of fabricated chips. To the best of our knowledge, this is the first proof-of-concept of RF test based on non-intrusive sensors.