Optimal signal-to-noise ratio for silicon nanowire biochemical sensors

The signal-to-noise ratio (SNR) for silicon nanowire field-effect transistors operated in an electrolyte environment is an essential figure-of-merit to characterize and compare the detection limit of such devices when used in an exposed channel configuration as biochemical sensors. We employ low frequency noise measurements to determine the regime for optimal SNR. We find that SNR is not significantly affected by the electrolyte concentration, composition, or pH, leading us to conclude that the major contributions to the SNR come from the intrinsic device quality. The results presented here show that SNR is maximized at the peak transconductance.     

杂散辐射功率测量方法

介绍标准规定的传统和改进的测量方法。理论与实际相结合,在测量准确度一致的前提下,比较两种测量方法的优缺点,得到了改进的测量方法比传统的测量方法更快速和高效的结论。对提高测量的专业水平和经济效益、促进行业的发展和科技创新都起到了一定的积极作用。     

Chi-squared-based filters for high-fidelity signal-to-noise ratio enhancement of spectra

When reconstructing a measured spectrum to enhance its signal-to-noise ratio (SNR), the objective is to minimize the variance between the smooth reconstructed spectrum and the original measured spectrum, hence to attain an acceptably small chi2 value. The chi2 value thus measures the fidelity of the reconstruction to the original. Smoothness can be conceived as attenuated variation between adjacent points in a spectrum. Thus, a conceptual change in the application of the chi2 function to the difference between adjacent points of the reconstructed spectrum permits its use, in principle, as both a measure of smoothness and a measure of fidelity. We show here that implementations of this concept produce results superior to Savitzky-Golay filters.     

Bistatic coherent laser radar signal-to-noise ratio

We investigate the signal-to-noise ratio (SNR) for a bistatic coherent laser radar (CLR) system. With a bistatic configuration, the spatial resolution is determined by the overlap of the transmit beam and the virtual backpropagated local oscillator beam. This eliminates the trade-off between range resolution and the bandwidth of the transmitted pulse inherent in monostatic systems. The presented analysis is completely general in that the expressions can be applied to both monostatic and bistatic CLR systems. The heterodyne SNR is computed under the assumption of untruncated Gaussian optics and untruncated Gaussian beam profiles. The analysis also includes the effects of refractive turbulence. The results show that, for maximum SNR, small transmit and local oscillator beam profiles (e-1 intensity radius) are desired.     

Generalized signal-to-noise ratio for spectral sensors with correlated bands

Traditional spectral sensors are intentionally designed to minimize overlap among spectral response functions of different bands. In contrast, some emerging classes of spectral sensors exhibit significant band overlap. An effect introduced by such band overlap is that the photodetector noise of one band is coupled into the others in subsequent data processing steps. Because of this, the traditional band-by-band definition of signal-to-noise ratio (SNR) cannot fully describe the detector's noise level. We devise a general definition of SNR in spectral space based on a recently developed geometrical spectral imaging model [J. Opt. Soc. Am. A24, 2864 (2007)]. With this model, we can find an orthogonal basis of the spectral response functions for the spectral sensor with decreasing instrument SNRs. We can also define the average instrument SNR for the whole sensor, which makes it possible to characterize quantitatively the photodetector noise of a spectral sensor with correlated bands.     

Estimation of analogue-to-digital converter's signal-to-noise plus distortion ratio using the code histogram method

A procedure is proposed to estimate an analogue-to-digital converter's signal-to-noise plus distortion ratio using the histogram method. The procedure provides results that are in close agreement with the ones obtained with the spectral analysis and sinewave fitting methods. It is shown that the errors obtained by using former implementations of the histogram method are due to not considering the input stimulus probability density function, and it is shown how these errors can be rectified.     

An adaptive window function method for power measurement

An adaptive window function for distorted power measurement is introduced in this paper. It can automatically provide the optimal window function according to the measured signal. Thus, the applied window function is always optimal in the sense of the zeros of its frequency response corresponding to the undesired measured signal spectrum components which will result in the harmful truncation errors. As a result, the harmful truncation errors of asynchronous sampling and the influence of interharmonics in the measured signal spectrum can be totally eliminated. The correctness, accuracy, and applicability of the proposed method have been verified both theoretically and by extensive simulations     

New method for reactive power and energy measurement

The properties of an electronic reactive power and energy measurement method based on a frequency-controlled power-to-pulse-rate conversion are analyzed. The reactive power and energy measurements can be efficiently performed by using a simple integrating circuit as a phase shifter, and frequency-controlled analog-to-pulse-rate converter. A low value of the output pulse rate should not be considered as an inherent disadvantage of the method. By introducing a phase-locked loop in order to achieve high pulse-rate output, the benefit of high resolution is added to the method. The improved electronic structure for the measurement can be implemented in the design of reactive power and energy standards. For precision var-hour meters based on the proposed method, it is possible to have an efficient error-checking and adjustment procedure. The proposed method allows reactive power and energy measurement to be made in single- and poly-phase, symmetrical and unsymmetrical, and balanced and unbalanced networks     

Maximum signal-to-noise ratio of a tape recorder

Using the Wiener autocorrelation theorem, the noise power spectrum of the pole strength in a thin lamina of an erased tape is shown to be approximately white. The noise power spectrum of the reproduce head voltage is calculated for a thick tape and compared with the signal power. The wide-band signal-to-noise ratio of a tape recorder equalized flat is deduced and expressed in very simple forms, which are inversely dependent upon the square of a bandwidth. Notably, in this special case the wide-band result is independent of reproduce head-to-tape spacing. Numerical examples demonstrate that this simple theory yields results in excellent agreement with practice.     

Discrepancies between two formulations of signal-to-noise ratio for background-limited detection

Different investigators have published different relationships for the same problem of predicting the signal-to-noise ratio for incoherent passive detection of infrared radiation. The results of two authors are compared, and a possible basis for the differences is explained.     

Maximum likelihood signal-to-noise ratio estimation for coded linearly modulated signals

In this study, the authors propose an exact maximum likelihood (ML) signal-to-noise ratio (SNR) estimator for coded linearly modulated signals. The estimator is expressed in terms of the marginal a posteriori probabilities (APPs) of the coded symbols, which can be obtained efficiently by the Bahl-Cocke- Jelinek-Raviv (BCJR) algorithm for codes defined on trellises. Simulation results show that the proposed ML code-aided (CA) SNR estimator significantly outperforms the non-data-aided (NDA) estimators in the low SNR regime. The Cramer-Rao bound (CRB) for CA SNR estimator is also derived and evaluated numerically. It is shown that the proposed ML-CA estimator performs very close to the derived bound. Comparisons of the CRBs for CA and NDA scenarios with different linearly modulated signals further illustrate the intrinsic performance improvement by exploiting the channel coding constraints.     

Detection signal-to-noise ratio versus bit cell aspect ratio athigh areal densities

As areal density in hard drives increases, the bit aspect ratio (BAR) becomes an increasingly critical design issue. In this paper, we use the detection signal-to-noise ratio (SNR) as a system-level indicator to establish the relationship between the optimal BAR and all major recording system parameters that relate to the head/medium combination and servo as well as the read channel. We address practical and fundamental issues including thermal stability, medium and additive system noise, and equalization and track misregistration. The results of our analysis generally agree with the recent consensus to move toward lower BARs but also caution that the optimal BAR is a strong function of the servo capability. The results of our BAR analysis also indicate that at high areal densities, the ratio of PW50 to the bit cell is considerably smaller than found in today's drives     

Optimized radiofrequency coils for increased signal-to-noise ratio in magnetic resonance microscopy

The signal-to-noise ratio (SNR) is a major obstacle to achieving increased resolution in magnetic resonance microscopy (MRM). The SNR considerations for MRM are presented, with particular attention to the role of judicious receiver coil design in maximizing sensitivity and limiting noise contributions both from the sample and the coil. We present a number of different coil configurations that have been optimized for particular applications of MRM in the biological sciences. An overview of the literature regarding derivations of the SNR for birdcage-configuration volume coils, inductively coupled surface coils, and surgically implanted coils is presented in a unified fashion. Microscopy coils designed to reduce the total volume of excitation, thus coupling more closely to a given region of interest, are discussed. The volume coil is presented in terms of its application to lung imaging in small animals at 2 T and imaging of stroke at 7 T. The performance of traditional surface coils is demonstrated by application to spinal cord imaging in the rat. Finally, implanted coils are examined, as used in studies of the carotid arteries. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 277–284, 1997     

Hybrid multi/single layer array transducers for increased signal-to-noise ratio

In medical ultrasound imaging, two-dimensional (2-D) array transducers are necessary to implement dynamic focusing in two dimensions, phase correction in two dimensions and high speed volumetric imaging. However, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance, which decreases the transducer signal-to-noise ratio (SNR). We have previously shown that SNR is improved using transducers made from multi-layer PZT, due to their lower electrical impedance. In this work, we hypothesize that SNR is further increased using a hybrid array configuration: in the transmit mode, a 10 Omega electronic transmitter excites a 10 Omega multi-layer array element; in the receive mode, a single layer element drives a high impedance preamplifier located in the transducer handle. The preamplifier drives the coaxial cable connected to the ultrasound scanner. For comparison, the following control configuration was used: in the transmit mode, a 50 Omega source excites a single layer element, and in the receive mode, a single layer element drives a coaxial cable load. For a 5x102 hybrid array operating at 7.5 MHz, maximum transmit output power was obtained with 9 PZT layers according to the KLM transmission line model. In this case, the simulated pulse-echo SNR was improved by 23.7 dB for the hybrid configuration compared to the control. With such dramatic improvement in pulse-echo SNR, low voltage transmitters can be used. These can be fabricated on integrated circuits and incorporated into the transducer handle.     

Method for optical signal-to-noise ratio monitoring based on modulation spectrum assessment

A novel method for optical signal-to-noise ratio monitoring is presented. The method is based on twofilter narrowband filtering which, combined with the knowledge of the modulation format, allows the determination of the amount of amplified spontaneous emission noise in the channel spectrum. The major advantage of the method is simplified experimental setup. The robustness of the method against various signal impairments is discussed and assessed through simulation. It is shown that the method provides sufficient accuracy for most practical applications and is remarkably resilient against other physical phenomena reducing signal quality. In particular, the method is inherently insensitive to chromatic dispersion and polarisation-related impairments. All results are presented for 10 Gb/s return-to-zero format.     

Polarization-discrimination technique to maximize the lidar signal-to-noise ratio for daylight operations

The impact and potential of a polarization-selection technique to reduce the sky background signal for linearly polarized monostatic elastic backscatter lidar measurements are examined. Taking advantage of naturally occurring polarization properties in scattered skylight, we devised a polarization-discrimination technique in which both the lidar transmitter and the receiver track and minimize detected sky background noise while maintaining maximum lidar signal throughput. Lidar elastic backscatter measurements, carried out continuously during daylight hours at 532 nm, show as much as a factor of square root 10 improvement in the signal-to-noise ratio (SNR) over conventional unpolarized schemes. For vertically pointing lidars, the largest improvements are limited to the early morning and late afternoon hours, while for lidars scanning azimuthally and in elevation at angles other than vertical, significant improvements are achievable over more extended time periods with the specific times and improvement factors depending on the specific angle between the lidar and the solar axes. The resulting diurnal variations in SNR improvement sometimes show an asymmetry with the solar angle that analysis indicates can be attributed to changes in observed relative humidity that modifies the underlying aerosol microphysics and observed optical depth.     

Contrast and signal-to-noise ratio in long-distance starlight imaging

A small telescope on an airplane or in low Earth orbit can, in principle, resolve ground objects under starlight with useful resolution. For an ~50-cm aperture and ~100-s exposure, one can obtain a resolution of tens of centimeters from an aircraft and a few meters from orbit. Such starlight images are photon poor, and feature detection depends on photon statistics. Scattered light, atmospheric absorption, and foreground airglow all degrade image contrast. I report an investigation into image signal-to-noise ratio using first-order analytical approximations. We find that, for a given angular resolution, the signal-to-noise ratio for spaceborne images is degraded approximately a factor of 1.7, compared with airborne images, by foreground airglow. Image signal-to-noise ratio improves as the passband moves to the red and as skies become brighter from artificial illumination.     

A stable differentiator with a controllable signal-to-noise ratio

The feedback properties of operational amplifiers are used in the construction of the differentiator. The basic concept, however is device-independent. Utilizing the tracking properties of feedback and using an integrator for a plant, the resulting error signal will approximate the derivative of the input. The system is stable for positive values of the gain. The signal-to-noise ratio (S/N) is controllable and is inversely proportional to the cubic power of the unity-gain bandwidth. The differentiator can have a higher frequency range of operation than is possible with other methods of design