Processing gain of surface-acoustic-wave convolver with noise-corrupted reference waveform

An analysis is given for the output signal/noise ratio of a convolver when both input waveforms are accompanied by noise. It is shown that a close approximation to the ideal matched-filter performance can be obtained if the signal/noise ratio at the reference input is only 10 dB. Experimental measurements support the analysis.     

Measuring audio SNR on digital broadcast systems

A spectrum analysis technique is described which will measure the quantization noise in a digital audio system with a signal present. An estimate of the power density spectrum is interpreted to find the signal to quantization noise ratio. Additional information derived from real life spectrum measurements is explained     

WDM EDFA gain characterization with a reduced set of saturating channels

The advent of EDFA-based dense WDM places demanding optical source requirements for EDFA characterization. An iterative method is proposed here, based on a homogeneous amplifier model, to calculate the required signal conditions for WDM testing with a reduced set of saturating channels and a broad-band noise probe. EDFA gain measurements demonstrating this reduced-source technique agree to within 0.2 dB to those obtained with a four-channel WDM system operating near 1.55 /spl mu/m.     

Sensitivity improvement in digital microwave signal analysis

Sensitivity in digital microwave signal analysis strongly depends on the signal/noise ratio. The letter describes a method which improves the signal/noise ratio and therefore the sensitivity of monofrequent amplitude and phase measurements by means of sampling below the Nyquist frequency.     

Experimental evaluation of echo path modeling with chaotic codedspeech

An experimental evaluation of an echo-path modeling device is reported for chaotically-coded speech telephony circuits. The device provides an accurate characterization of the far-end echo path using only half-duplex near-end speech during conversational calls. The in-service nonintrusive systems of interest are usually based on a class of least-mean-square (LMS) digital adaptive filters (DAFs). The chaotic-based modulation regime exploits a logistic mapping to optimize the convergence rate of the model while preserving the signal bandwidth requirements. Experimental results show that uncoded speech is ineffective in driving the modeling device when noise-to-echo ratios exceed approximately -30 dB and thus invalidates live measurements. The chaotic modulation, however, increased the echo-to-noise ratio and allowed adaptation for far-end noise conditions exceeding 30 dBs higher than that of the uncoded case     

Quantization Noise Suppression in Digitally Segmented Amplifiers

In this paper, we consider the problem of out-of-band quantization noise suppression in the general family of direct digital-to-RF (DDRF) conversion circuits, where the RF carrier is amplitude modulated by a quantized representation of the baseband signal. Hence, it is desired to minimize the out-of-band quantization noise in order to meet stringent requirements such as receive-band noise levels in frequency-division duplex transceivers. In this paper, we address the problem of out-of-band quantization noise by introducing a novel signal-processing solution, which we refer to as “segmented filtering (SF).” We assess the capability of the proposed SF solution by means of performance analysis and results that have been obtained via circuit-level computer simulations as well as laboratory measurements. Our proposed approach has demonstrated the ability to preserve the required signal quality and power amplifier (PA) efficiency while providing more than 35-dB attenuation of the quantization noise, thus eliminating the need for substantial post-PA passband RF filtering.      

AlGaN/GaN异质结紫外探测器

采用p-AlxGa1-xN/i-GaN/n- GaN异质结构成功制备了含铝组分分别为0.1和0.07的正照射可见盲紫外探测器，并分别测试了它们的伏安特性曲线和光电响应光谱。对于Al组分为0.1的器件，在零偏压处出现了极低的暗电流密度，表明器件具有非常高的信噪比。高分辨率X射线衍射仪对材料的测试结果表明，高铝组分(0.1)窗口层薄膜材料的晶体质量较差，导致暗电流增大，而其窗口层的窗口选择作用则可以得到较高的响应率和较宽的响应波段。     

Frequency-dependent SNR for time-base distortions in magnetic recording

Time-base distortions are modelled with a linear, time-invariant system plus an uncorrelated but signal-dependent disturbing noise. The signal/noise ratio (SNR) in this model is computed and the theoretical results are compared with laboratory measurements of flutter effects in analogue magnetic recorders.     

A third-order sigma-delta modulator with extended dynamic range

Oversampling modulators based on high-order sigma-delta modulation provide an effective means of achieving high-resolution analog-to-digital conversion in VLSI technology. Because high-order noise shaping greatly reduces the quantization noise in the signal band, the dynamic range of these modulators tends to be bounded by the thermal noise of the input stage and the maximum voltage swing in the signal path. This paper introduces a third-order cascaded sigma-delta modulator that uses a modified cascaded architecture and reduced gain in the first integrator to increase the dynamic range. An experimental modulator fabricated in a 1-μm CMOS technology attains a resolution of 17 b for a 25-kHz signal bandwidth while operating from a single 5-V supply. With an oversampling ratio of 128 and a clock frequency of 6.4 MHz, the modulator achieves a 104-dB dynamic range and a peak signal-to-noise+distortion ratio (SNDR) of 98 dB. As indicated by both measurements and simulations, the cascaded architecture also greatly reduces the discrete noise peaks that can be present in a single-stage architecture     

Analog PAL-G signal degradation due to spread spectrum overlay

Performance degradation of an analog PAL-G signal due to direct sequence spread spectrum overlay is examined. An analytical expression between RF TV protection ratio (CIR) and baseband unweighted signal-to-noise ratio (SNRv), for co-channel spread spectrum and noise interference, is derived. Computer analysis results are presented and compared to experimental measurements for different spread spectrum RF bandwidths and carrier frequency offsets between the analog and digital signal. Image quality degradation is also presented and associated to different level of spread spectrum interference.     

Robust estimation of fetal heart rate variability using Doppler ultrasound

This paper presents a new measure of heart rate variability (HRV) that can be estimated using Doppler ultrasound techniques and is robust to variations in the angle of incidence of the ultrasound beam and the measurement noise. This measure employs the multiple signal characterization (MUSIC) algorithm which is a high-resolution method for estimating the frequencies of sinusoidal signals embedded in white noise from short-duration measurements. We show that the product of the square-root of the estimated signal-to-noise ratio (SNR) and the mean-square error of the frequency estimates is independent of the noise level in the signal. Since varying angles of incidence effectively changes the input SNR, this measure of HRV is robust to the input noise as well as the angle of incidence. This paper includes the results of analyzing synthetic and real Doppler ultrasound data that demonstrates the usefulness of the new measure in HRV analysis.     

N-MOSFET oxide trap characterization induced by nitridation process using RTS noise analysis

This paper presents oxide trap characterization of nitrided and non-nitrided gate oxide N-MOSFETs using low frequency noise (LFN) measurements. The identification of defects generated by the gate oxide growth and the nitridation process is carried out using random telegraph signal noise analysis. Significant properties of traps induced by the nitridation process are pointed out. Main trap parameters, such as their nature, capture and emission times, cross-sections, energy levels, and position with respect to the Si/SiO₂ interface, are extracted. These results illustrate the potential of noise investigation for oxide characterizations.     

Confidence intervals for the signal-to-noise ratio when a signalembedded in noise is observed over repeated trials

The problem of estimating the signal-to-noise ratio (SNR) when repeated measurements are made of a deterministic signal embedded in random noise is considered. An estimator is described, its asymptotic distribution is derived, and a method for constructing confidence intervals is proposed. The performance of the method is evaluated using simulated evoked potential data, and an application to real evoked potential data is presented     

In situ characterization of laser diodes from wide-band electrical noise measurements

The wide-band electrical noise characteristics of 0.8-, 1.3-, and 1.5-μm laser diodes have been studied theoretically and for the first time also experimentally. The electrical noise is related to the optical intensity noise behavior, and can therefore be used for in situ measurements and characterization of laser diodes. Since the measurements are performed without any optical components, undesired optical feedback is eliminated. The results show that several important laser parameters and characteristics can be extracted from purely electrical noise measurements. Among these are the relaxation frequency, the threshold current, the emission linewidth, optical feedback properties, and longitudinal mode hopping behavior. Good agreement between the noise theory and the electrical noise measurements has been obtained. An expression for obtaining both the spectral linewidth and lineshape from electrical noise measurements is also derived.     

Transimpedance amplifier-based full low-frequency noisecharacterization setup for Si/SiGe HBTs

An experimental setup, based on current/voltage conversion through transimpedance amplifiers (TAs), has been implemented for the direct full low-frequency noise (LFN) characterization of Si/SiGe heterojunction bipolar transistors (HBTs) in terms of base and collector short-circuit current noise sources. This setup performs a full characterization, as it measures simultaneously the two noise current sources and their correlation, thanks to an original technique based on the specific properties of a specially designed buffer amplifier using a low-noise common-base bipolar transistor (CB BJT). By means of translation formulae, the obtained measurements are compared with those carried out with a multi-impedance technique. They show a good agreement both for the noise sources spectral densities and for their correlation. The TA-based setup provides enhanced capabilities in terms of measurement speed and remote control potentialities     

2.5 V passive CMOS mixer with 20 dBm P1 dB compression

A passive CMOS downconversion mixer with LO buffer is presented in 0.25 μm SiGe BiCMOS using a 2.5 V supply. With a 60 MHz RF signal input, measurements show that the conversion loss is 2.9 dB, the input-referred 1 dB compression point is 20 dBm and the inputreferred noise is 2146.8 dBm/Hz. Compared to conventional NMOS mixers, the 1 dB compression point is improved by 9.7 dB. The tradeoffs and the design of the LO buffer, which has a strong impact on the intermodulation distortion, are also presented.     

On the ‘excess white noise’ in MOS transistors

Special silicon MOS transistors are fabricated to demonstrate that the proposed ‘excess white noise’ attributed to the mobility fluctuation does not exist. The previously observed excess noise over the white thermal noise is shown to be caused by a 1/f-type noise component due to noise measurements at insufficiently high frequencies on devices which have very high 1/f noise.     

Signal processing in the reflective acoustic microscope

We describe a new technique to enhance the image in the scanning acoustic microscope in the reflection mode. We use a 20 ns pulse modulated r.f. signal and a sampling oscilloscope to separate the incident signal from the reflected signal. The resulting image shows up details that are of the order of one micrometre with a good signal/noise ratio. We can further improve this resolution by phase measurements.     

Comparison of noise characteristics of Fabry-Perot-type and travelling-wave-type semiconductor laser amplifiers

We report results of comparative noise measurements on AlGaAs semiconductor laser amplifiers of the Fabry-Perot and travelling-wave types. We show that, for the same net gain, the electrical baseband signal/noise ratio of a photodetector placed at the amplifier output (after an optical filter) is higher for a travelling-wave-type amplifier, especially at high-gain values where the Fabry-Perot amplifier is operated at oscillation threshold. For a net gain of 20.5 dB, the signal/noise ratio of the travelling-wave-type amplifier is 4?5 dB better.     

Thermal noise of a silicon double-injection plasma diode

Measurements of the thermal noise of a silicon p⁺−π−n⁺ diode operating in the Lampert-insulating regime agree within 6 per cent with the prediction S_i = 4kT Re(Y). The noise measurements were performed in the cube-law regime with d.c.-currents from 100 μA to 4mA at room temperature.