Vishwanath Natarajan

Pro-VIZOR: process tunable virtually zero margin low power adaptive RF for wireless systems

In this paper, a process tunable, continuously adaptive wireless front end architecture and related adaptation algorithms are presented that allow an RF transceiver to function at minimum power irrespective of channel conditions and process variability induced performance loss in the RF front end and baseband interface. Current wireless transceiver front ends are designed for worst case channel conditions and a limited degree of post manufacture tuning is performed to compensate for process variations. It is shown how the proposed architecture can result in significant power savings over current practice without compromising system-level bit error rate. The adaptation methodology is applied to a WLAN transceiver design and hardware measurement data for an adaptive receiver is presented.

Analog Signature- Driven Postmanufacture Multidimensional Tuning of RF Systems

Tuning knobs are becoming common in analog and RF devices for postsilicon calibration for variation tolerance and compensation. This article presents a low-cost, hardware-iterative technique based on a steepest-descent-based gradient search algorithm and demonstrates its utility in performance tuning of a 2.4-GHz transmitter system.

Alternate electrical tests for extracting mechanical parameters of MEMS accelerometer sensors

Recent advances in thin film micromachining techniques have spurred a new generation of smart systems incorporating microelectromechanical systems (MEMS). Extracting the mechanical properties of MEMS devices has always been a challenge in terms of test time and test cost due to difficulties associated with accurate characterization of thin films. This paper describes a novel technique for diagnosing the mechanical parameters of a cantilever-beam accelerometer using purely electrical test stimulus. The beam is stimulated with an optimized test stimulus, generated by a gradient-based search method. The response measurements made on the MEMS device are mapped to the mechanical properties of the beam using a regression-based mapping technique. Using this method, the mechanical parameters associated with the beam can be estimated within an accuracy of 5% of their actual values. In addition, the test approach is amenable to a compact built-in test solution.

Optimized Multitone Test Stimulus Driven Diagnosis of RF Transceivers Using Model Parameter Estimation

Test time and test complexity reduction has become a critical challenge in modern RF testing. Prior “alternative” test methods have achieved fast testing at the cost of using supervised learning algorithms that require “training”. In contrast, behavioral model parameter estimation based test methods require the use of accurate models but no “training” is necessary, reducing test deployment costs. In this work, a new test generation approach is proposed that allows behavioral model parameter estimation to be performed from a single optimized OFDM data frame. A genetic multi-tone test stimulus optimization algorithm is developed to maximize the accuracy with which a nonlinear solver can determine RF transceiver model parameters from raw downconverted test response data. The transceiver model proposed is the most comprehensive to date and includes AM-PM distortion and 5th order nonlinearity effects. Simulation results show that using the optimized multitone test stimulus, all the model parameters can be computed accurately using a single data acquisition (4X-5X faster than prior parameter estimation techniques and comparable to alternative test times). Data from an experiment performed on a hardware prototype validates the proposed concept.

A holistic approach to accurate tuning of RF systems for large and small multiparameter perturbations

In this paper, a holistic yield recovery approach based on post manufacture tuning of RF circuits and systems under large as well as small multi-parameter process variations is developed. Marginally failing devices (small parameter deviations) are tuned using a nonlinear “Augmented Lagrange” algorithm driven optimization engine that includes test specification values and power consumption in its optimization framework. A novel built-in alternate tuning test is used to explicitly evaluate all the DUT specifications at each optimization iteration. For large parameter deviations well beyond the test specification limits of the DUT, determination of the different specification values is difficult. Such devices are tuned using a golden response tuning approach which optimizes the DUT specifications implicitly until the DUT is “good enough” to be tuned by the prior Augmented Lagrange algorithm. The proposed methodology enables yield recovery of devices not possible with earlier methods, avoids local minima and can be implemented at low cost.

Iterative built-in testing and tuning of mixed-signal/RF systems

Design and test of high-speed mixed-signal/RF circuits and systems is undergoing a transformation due to the effects of process variations stemming from the use of scaled CMOS technologies that result in significant yield loss. To this effect, postmanufacture tuning for yield recovery is now a necessity for many high-speed electronic circuits and systems and is typically driven by iterative test-and-tune procedures. Such procedures create new challenges for manufacturing test and built-in self-test of advanced mixed-signal/RF systems. In this paper, key test challenges are discussed and promising solutions are presented in the hope that it will be possible to design, manufacture and test “truly self-healing” systems in the near future.

BIST Driven Power Conscious Post-Manufacture Tuning of Wireless Transceiver Systems Using Hardware-Iterated Gradient Search

In this paper, a fast RF BIST-driven post-manufacture tuning methodology for yield improvement of RF transceiver systems is presented. The core algorithms optimize multiple transceiver performance metrics concurrently using a hardware-iterated gradient search algorithm that uses diagnostic BIST data to guide the tuning of circuit and software level parameters. Intelligent “initial guess” values for the circuit and software tuning knobs at the start of the tuning process allow rapid convergence. Power consumption is given key consideration through the tuning process. Further, self-tuning is performed with little or no external tester support. The viability of the proposed scheme has been demonstrated through an experimental RF hardware prototype. Experimental results demonstrate significant yield recovery while allowing up to 10X savings in test/tuning time.

Yield Recovery of RF Transceiver Systems Using Iterative Tuning-Driven Power-Conscious Performance Optimization

This paper proposes a fast and low-cost method of calibrating RF transceiver systems using on-chip DSP resources and some additional circuit control points. Experimental results on a commercial power amplifier demonstrate significant increases in production yields using the proposed approach.

Digitally Assisted Concurrent Built-In Tuning of RF Systems Using Hamming Distance Proportional Signatures

In this paper, a novel built-in tuning technique to compensate for variability induced imperfections in RF subsystems is proposed. The test stimulus is obtained from a filtered digital pattern and the RF response is down-converted using an envelope detector. The resulting signal is mapped to a digital signature, such that the Hamming Distance between the observed and the golden signature represents the degree by which the circuit specifications (Gain, IIP3, EVM, etc) differ from the ideal. A hardware driven algorithm is used to minimize this Hamming Distance to concurrently optimize (tune) multiple RF specifications. As opposed to prior research, the method does not require the use of an on-chip digital signal processor and uses minimal on-chip hardware. Results obtained on a 2.4 GHz transmitter subsystem show significant impact of tuning on device specifications.

A theoretical study of structural and electronic properties of pentacene/Al(100) interface.

The first principle calculations within the framework of density functional theory have been performed for the pentacene molecule deposited on the aluminum Al(100) substrate to study the structural and electronic properties of the pentacene/Al(100) interface. The most stable configuration was found at bridge site with 45° rotation of the pentacene molecule on Al(100) surface with a vertical distance of 3.4 Å within LDA and 3.8 Å within GGA functionals. The calculated adsorption energy reveals that the adsorption of pentacene molecule on Al(100) surface is physisorption. For the stable adsorption geometry the electronic properties such as density of states (DOS), partial density of states (PDOS), Mulliken population analysis and Schottky barrier height are studied. The analysis of atomic charge, DOS and PDOS show that the charge is transferred from the Al(100) surface to pentacene molecule, and the transferred charge is about -0.05 electrons. For the adsorbed system, the calculated Schottky barrier height for hole and electron transport is 0.27 and 1.55 eV, respectively.