Bhaskar Choubey

Modelling of high dynamic range logarithmic CMOS image sensors

The quality of the output images from high dynamic range logarithmic sensors is limited by fixed pattern noise (FPN) which is caused by device mismatches within pixels in an array. It leads to inferior image quality in comparison to image from other sensors of similar resolution. Previous design and post-chip attempts to correct this type of noise have been either impractical or resulted in other complexities. However, FPN correction can be attempted using an accurate model approach for the response of this type of pixel. A three parameter model, previously suggested for logarithmic pixels, has been tried for this purpose. In this paper a simple parameter extraction procedure is proposed using this model to calibrate and correct FPN. The result is a model that works well over six decades of illumination but fails at high photocurrents. It is shown that this is caused by a breakdown in an assumption used to create the three parameter models. Consequently, a new four parameter model is developed that fits the data over six decades, and is usable in FPN correction for many wide current range applications that require complete and accurate characterisation.

Characterization of coupled micro/nanoresonators using inverse eigenvalue analysis

This paper reports a method of determining the system matrix of a nearest neighbor coupled array of micro/nanomechanical resonators. The simple method requires contacts to only one element of the array to determine two sets of eigenvalues related to the system matrix. The elements of the system matrix are then determined from these eigenvalues. This system matrix can then be used to determine the characteristics of the individual resonators or as the starting point for a perturbation analysis to determine the changes observed when a functionalized array of resonators is used as a sensor.

Low dark current logarithmic pixels

The sensitivity of logarithmic pixels at low light levels is limited by the dark current that flows through the load transistor in the pixel in parallel with the photocurrent. A new layout for a logarithmic pixel is reported that significantly reduces the dark current in the pixel. In addition a simple change to the bias voltages applied to the pixel means that the new layout can simultaneously exhibit a linear response to low-light levels and a logarithmic response at higher light levels.

Interocular transfer of orientation-specific fMRI adaptation reveals amblyopia-related deficits in humans

We devised an experimental strategy for assessing the cortical cross-talk between ocular subsystems. For this purpose we measured the interocular transfer of adaptation (IOTA) at different levels in the human brain, using orientation-selective fMRI adaptation. We tested 10 normally sighted and 10 stereoblind or stereodeficient amblyopic observers by adapting monocularly to phase-reversing, oblique sinusoidal gratings. Following monocular adaptation, cortical activations evoked by the same (monoptic) or the other eye (interocular) were measured for the same and for the orthogonal orientation in a two by two factorial design. In both experimental groups, we obtained significant orientation-selective monocular adaptation in area V1 and in extrastriate regions on the dorsal and ventral visual pathways. In the normally-sighted subjects we found in addition interocular adaptation in V1 and extrastriate visual areas. This interocular adaptation indicates that fMRI adaptation transfers from the adapted ocular subsystem to the non-adapted ocular subsystem, and thus provides a measure of binocular interaction in normally-sighted subjects. In the amblyopic subjects, no interocular adaptation was seen at any of the investigated cortical levels, regardless of which eye was adapted. We suggest that the abnormal pattern of interocular transfer of fMRI adaptation is related to the disturbed integration of binocular signals in amblyopia.

Determination of the Anisotropy of Young's Modulus Using a Coupled Microcantilever Array

This paper reports a simple technique to measure the anisotropy of the Youngs modulus of MEMS materials using coupled cantilevers. The technique is demonstrated in single-crystal silicon with an array of cantilevers fabricated in (100) silicon following a “wagon wheel” configuration. The long axis of the cantilevers had different angular orientations to the [110] direction. The parasitic coupling due to undercut below the cantilevers, which is often observed during etching of MEMS, led to a collective behavior in the frequency response of the cantilevers. This collective behavior was used in association with an inverse eigenvalue analysis to obtain the Youngs moduli for the different orientations. Further analysis of the technique relating to accuracy and precision required in the resonance frequency measurement has also been presented.

Secure User Authentication in Internet Banking: A Qualitative Survey

—A qualitative survey of user identification mechanisms being applied in online banking environments across the English speaking world is presented. By studying the Internet banking sites of most major banks in 7 countries, the paper reports the variations and calls for standardisation of user credentials in these environments. I INTRODUCTION Internet based technologies have revolutionised the banking industry as well as way people interact with financial institution and one another financially. However, it has raised new questions and dimensions for securing data of the financial institutions as well as the end-users. In this paper, we raise the oft-repeated question of security in online banking systems, which have been extensively studied from technological, sociological, financial and other points of views. [1]-[7]. Security covers a large spectrum of activity in banking. At one end of this spectrum is the back-end security infrastructure being applied at the banking institutions to secure their databases and servers. Somewhere in between are the encryption based security features which ensure the safety and security of data transmission between the bank and the end-user. The other end of the spectrum is the end-user him/herself. A major concern of every bank is the proper authentication of its end-user in a secure environment. The end-user is also concerned that no one else should be able to access his account [3], [8]. In this paper, we study this end of the spectrum; more specifically, we study the identification mechanism in online banking systems. For any non-personal transaction, the bank has to verify the identification of the end-user, and hence in an online environment has to trust some form of digital identity to know its customer. More importantly, it has to ensure that the form of identity has not been tampered with. Several solutions have been suggested and are being used by banks across the globe to verify the identity of its customers [2]. In this paper, we survey these features; however, we limit ourselves to the features in use in various banks and discard the ones proposed only in technical literature [1], [9]. The second section of the paper provides the methodology of our qualitative study. The third section followed by a description of the identification credentials being used by the banks. The fourth section of the paper discusses the way in which these login credentials are sought. Finally, a discussion is provided at the end of the paper. II DATA …

Methods for dichoptic stimulus presentation in functional magnetic resonance imaging - a review.

Dichoptic stimuli (different stimuli displayed to each eye) are increasingly being used in functional brain imaging experiments using visual stimulation. These studies include investigation into binocular rivalry, interocular information transfer, three-dimensional depth perception as well as impairments of the visual system like amblyopia and stereodeficiency. In this paper, we review various approaches of displaying dichoptic stimulus used in functional magnetic resonance imaging experiments. These include traditional approaches of using filters (red-green, red-blue, polarizing) with optical assemblies as well as newer approaches of using bi-screen goggles.

On Characterizing Microelectromechanical Processes Using Coupled Resonators

In this paper, a simple method of measuring process-induced variations is proposed using a chain of nominally identical microelectromechanical resonators. The method is based upon the fact that the n eigenfrequencies of a chain of mechanically coupled resonators can be determined from the response of only one resonator in the chain. However, these n values do not provide enough information to determine the 2n - 1 elements of the system matrix. The extra information needed to obtain the system matrix is therefore obtained by perturbing the characteristics of one of the resonators and measuring the resulting eigenfrequencies. A resonator whose effective spring constant can be perturbed by varying an applied voltage has therefore been used to validate the proposed method. The validity of the proposed method is then demonstrated in several different ways. First, the extracted system matrix is used to predict the effects of perturbations to one or more of the resonators. Second, the eigenvectors of the system matrix are shown to correspond to the measured eigenmodes of the system. Finally, it is shown that, as expected, a change to one resonator only changes the corresponding diagonal element of the system matrix. Most importantly, this test shows that the method can determine the critical diagonal elements of a system matrix to an accuracy of 0.1%.

A pilot study for investigating cortical binocularity in humans using fMRI adaptation.

Disrupted stereovision is a feature that accompanies strabismus. This study uses an fMRI adaptation paradigm to assess the amount of cortical binocularity in subjects with normal or impaired stereopsis. We present data from a pilot study of two normally-sighted and one stereodeficient subject with alternating fixation. We adapted one eye to diagonally oriented sinusoidal gratings and tested either the same (monocular test) or the other eye (interocular transfer), using either the same or an orthogonal orientation. In normally-sighted subjects, we observed monocular adaptation but only weak interocular transfer in the striate cortex, whereas in the extrastriate cortex we found strong monocular as well as interocular adaptation. In the stereodeficient subject, monocular adaptation but no interocular transfer was obtained in the extrastriate cortex. These results suggest that impaired stereopsis is related to reduced interocular transfer of adaptation at higher levels of the cortical visual pathway.

A Simple Technique to Readout and Characterize Coupled MEMS Resonators

Highly sensitive microelectromechanical system (MEMS) resonators have been used for extensive applications such as mass sensing. However, these arrays are prone to process variations and are difficult to characterize due to lack of connections with each resonator. Coupled array of such sensors can enhance functionality while reducing interconnections. This scheme allows a number of sensors to be read out using a single input/output channel. By perturbing the spring constant of one resonator, two sets of eigenvalues can be measured to reconstruct the system matrix of the coupled system. However, perturbation on MEMS devices can introduce non-linear or physical change. To prevent such undesired change, this paper proposes a technique to couple an electrical resonator to an array of MEMS resonators. Two sets of eigenvalues can therefore be measured by simply connecting/disconnecting the electrical resonator. Errors introduced by frequency noise, array size, coupling strength, and damping have been analyzed. The successful coupling between electrical and mechanical resonators brings huge promise for integrated MEMS devices that could be used for single input/output multi-sensor and monitoring variations in MEMS fabrication.