Improvement of signal-to-noise ratio by stochastic resonance in sigmoid function threshold systems, demonstrated using a CMOS inverter

Stochastic resonance (SR) has become a well-known phenomenon that can enhance weak periodic signals with the help of noise. SR is an interesting phenomenon when applied to signal processing. Although it has been proven that SR does not always improve the signal-to-noise ratio (SNR), in a strongly nonlinear system such as simple threshold system, SR does in fact improve SNR for noisy pulsed signals at appropriate noise strength. However, even in such cases, when noise is weak, the SNR is degraded. Since the noise strength cannot be known in advance, it is difficult to apply SR to real signal processing. In this paper, we focused on the shape of the threshold at which SR did not degrade the SNR when noise was weak. To achieve output change when noise was weak, we numerically analyzed a sigmoid function threshold system. When the slope around the threshold was appropriate, SNR did not degrade when noise was weak and instead was improved at suitable noise strength. We also demonstrated SNR improvement for noisy pulsed voltages using a CMOS inverter, a very common threshold device. The input-output property of a CMOS inverter resembles the sigmoid function. By inputting the noisy signal voltage to a CMOS inverter, we measured the input and output voltages and analyzed the SNRs. The results showed that SNR was effectively improved over a wide range of noise strengths.     

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A new arc detector with ultra wide dynamic range was developed based on three gain adjustable amplifiers and microcontroller for the RF (radio frequency) windows in the high-power microwave heating systems on HL-2A/M tokamak. The gain is digitally adjustable with 8 levels in the main amplifier and the protection threshold is adjustable from 0 to 5V with accuracy of 20mV. Both the gain and threshold are remotely controlled with the help of a microcontroller. The measured maximum response time is 2.56μs. The arcing detectors work properly in different level of background light and in complicated electromagnetic environment.     

大动态范围数控弧光探测器的研制

针对HL-2A/M 高功率微波加热系统微波窗口真空侧对弧光探测的要求,基于三级放大电路和微控制器技术,完成电路设计,研制了新型弧光探测器。增益8 挡数字可调,保护阈值以20mV 的精度0~5V 数字可调,具有远程操作和数字显示功能。在不同增益和保护阈值条件下,实验测得其响应时间最大为2.56μs,能在复杂电磁环境和不同强度干扰光的条件下稳定工作,满足系统要求。     

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为了解决在功率测量中检波器输出的非线性曲线和动态输入功率范围小等问题,为500k W/3.7GHz的LHCD系统设计了对数检波器,并由其组成新型线性微波功率测量系统。测试结果表明,该测量系统具有更大的动态功率测量范围,其特征曲线在本系统功率参数内具有优良的线性特性,对数一致性误差在-1d B~+1d B范围内可输入微波功率动态范围>40d B,在系统可用范围内利用线性拟合获得的相关系数大于0.999。该结果优于以前设备测试结果。     

HL-2A 装置LHCD 微波功率测量系统设计

为了解决在功率测量中检波器输出的非线性曲线和动态输入功率范围小等问题,为500kW/3.7GHz 的LHCD 系统设计了对数检波器,并由其组成新型线性微波功率测量系统。测试结果表明,该测量系统具有更大的动态功率测量范围,其特征曲线在本系统功率参数内具有优良的线性特性,对数一致性误差在-1dB~+1dB 范围内可输入微波功率动态范围>40dB,在系统可用范围内利用线性拟合获得的相关系数大于0.999。该结果优于以前设备测试结果。     

信号调制色泵噪声和实虚部间关联量子噪声驱动下单模激光的随机共振现象

计算了受信号调制的色泵噪声和实虚部间关联的量子噪声驱动的单模激光损失模型的输出光强信噪比.发现信噪比R随泵噪声自关联时间τ、调制信号频率Ω和量子噪声实虚部间关联系数λq的变化均存在随机共振,这种现象扩展了“信噪比R对噪声强度的变化曲线具有极大值”的典型随机共振. 若以Ω为参数,当Ω增加时,Ｒ随τ的关系曲线经历了从同时出现共振和抑制到单峰共振,最后到单调上升的变化,呈现多种形式的随机共振．若以τ为参数,当τ增加时,Ｒ随Ω的关系曲线经历了从单调上升到同时出现共振和抑制,最后又到单调下降的变化过程．Ｒ随λq的关 关键词： 噪声 信噪比 随机共振     

Diffuse surface calibration method to improve accuracy and dynamic range of aerosol elastic light scattering measurements

A new method to calibrate detectors for elastic light scattering (ELS) measurement based on diffuse scattering from a Lambertian surface is presented. The method produces a calibration signal that is approximately seven orders of magnitude larger than a propane gas Rayleigh scattering calibration. The method also allows for calibration of detectors such as photodiodes, which are not sensitive enough to detect Rayleigh scattering for calibration but possess characteristics desirable for the measurement of soot ELS. Since the method is only suitable for backward scattering calibrations, transfer of calibration data from a backward- to a forward-oriented detector is accomplished with a secondary laser and integrating sphere. In demonstration experiments, calibration constants for photomultiplier tube (PMT) detectors obtained using both Rayleigh scattering and diffuse surface scattering agreed within experimental uncertainties as did measurements of in-flame scattering coefficients obtained with PMTs and photodiodes. However, achievable uncertainties with the diffuse-surface calibration approach were significantly reduced. More importantly, by enabling the use of photodiode detectors in ELS measurements, the new method facilitates operation at higher photon fluxes resulting in improved signal-to-noise ratios, reduced influence of photon shot noise, and the ability to achieve higher dynamic range in transient measurements.     

Coaxial holographic data storage without recording the dc components

A technique of recovering the data pages from Fourier holograms recorded without the dc components is demonstrated theoretically and experimentally by use of a coaxial holographic storage system. A reconstructed image is obtained by adding a phase-modulated dc component of the signal beam on reading. The bit error rate of the reconstructed image is comparable with that for the hologram recorded with the dc component as well. Since high intensities of the dc components are not recorded in this technique, the dynamic range of the recording media can be saved, which potentially contributes to increasing the number of multiplexed holograms.     

基于双平行马赫-曾德尔调制器的大动态范围微波光子下变频方法

为了提高微波光子下变频链路的性能,提出了基于集成双平行马赫-曾德尔调制器的微波光子下变频方法.通过理论推导和数值仿真分析了系统的增益和无杂散动态范围,实验搭建了基于双平行马赫-曾德尔调制器的下变频链路,控制直流偏置电压使双平行马赫-曾德尔调制器工作在高载波抑制的双边带调制模式,并对链路进行了性能测试.实验结果表明:该下变频链路的增益为7.43 d B,无杂散动态范围达到了110.85 d B/Hz2/3,工作频段可覆盖5—18 GHz的宽频范围.基于双平行马赫-曾德尔调制器的下变频方法可优化设计输出频谱,系统结构简单、易于实现,为微波光子下变频链路提供了有效的解决方案.     

Research on detection method of multi-frequency weak signal based on stochastic resonance and chaos characteristics of Duffing system

Weak signal detection has been widely used in many fields such as military and national economy. Aiming at the problem that the traditional stochastic resonance (SR) method can’t obtain the signal amplitude when detecting weak signals, the frequency and amplitude of the weak signal are obtained by combining the SR and chaos characteristics of the two-dimensional Duffing system. Firstly, the effects of two-dimensional Duffing system parameters a, b, k, noise intensity D on the Kramers rate and signal-to-noise ratio (SNR) are analyzed under the Gaussian white noise environment. The results show that the damping ratio K can hinder the SR effect of the system to some extent. Secondly, to solve the misjudgment of the state method of the weak signal amplitude in the detection, the Lyapunov exponent is used to assure the threshold's range, and the threshold of the chaotic critical state is found. Finally, the paper gives the processes of frequency and amplitude detection of multiple high-frequency signals, which realizes the effective detection of the frequency and amplitude of multiple high-frequency signals in a Gaussian white noise environment, and successfully applies the method to the accurate detection of boundary voltage amplitude in electrical impedance tomography.     

CMOS图像传感器时间域噪声分析及其应用研究

针对目前CMOS探测器的噪声研究绝大部分采取频率域的分析方法,所得的结果对于实际的探测器应用指导性不强。从时间域出发,构建了全新的探测器噪声模型,分析了在探测器的不同工作时期内噪声量大小同时间的关系。给出了探测器工作时序的优化准则,积分时间越长,系统的信噪比增加,输出信号电压值增大,等效输入端信噪比不变,系统的动态范围减小;复位时间越短,输出噪声量越小,但是图像的滞后效应也就越严重,在对弱小目标进行成像时应该尽可能地减少复位时间,增大积分时间,对于亮目标成像,应该增大复位时间,减少积分时间。     

PV型HgCdTe光电探测器中的混沌及其诊断

 对激光辐照半导体光电探测器的实验研究，发现当一束不太强的稳定连续波激光照射在PV型HgCdTe光电探测器上时，可以引起探测器出现混沌行为。利用光电探测器的光电压信号随时间变化的实验数据，通过求功率谱、计算Lyapunov指数对混沌进行了诊断。     

Radio-frequency muon spin resonance (RFμSR) experiments on condensed matter

In this paper we present an overview of the radio-frequency muon spin resonance (RFμSR) technique, an analogue to continuous-wave NMR, and an introduction to time-integral (TI) and time-differential (TD) RFμSR on muons in diamagnetic or in paramagnetic environments. The general form of the resonance line for TI-RFμSR as well as the expression for the time-dependence of the longitudinal muon spin polarization at resonance are given. Since RFμSR does not require phase coherence of the muon spin ensemble, this technique allows us to investigate muon species that are generated by transitions from, or in the course of reactions of, a precursor muon species even if in transverse-field (TF) μSR measurements the signal is lost due to dephasing. This ability of RFμSR is clearly demonstrated by measurements on doped Si. In this example, at low temperatures, a very pronounced signal from a muon species in diamagnetic environment has been found in RFμSR measurements, whereas in TFμSR experiments only a very small signal from muons in diamagnetic environment could be detected and a large fraction of the implanted muons escaped detection. These findings could be interpreted in terms of the delayed formation of a diamagnetic muonium-dopant complex, and, due to the large diamagnetic RFμSR signal, the RFμSR technique is a unique tool to study how the variation of parameters and experimental conditions such as illumination affects formation and behavior of these complexes. First results obtained on illuminated boron doped Si are reported. However, as illustrated by the example of experiments on the muonated radical in solid C₆₀, results from conventional TI-RFμSR cannot always be interpreted unambiguously since different parameters, namely the fraction of muons forming the investigated muon species, the longitudinal and the transverse relaxation rates, have similar effects on height and shape of the RFμSR resonance line. These ambiguities, however, may be resolved by collecting time-differential data. With this extension RFμSR becomes a very powerful complementary method to TFμSR in the studies of dynamic effects.     

基于Kramers逃逸速率的调参随机共振机理

根据Kramers逃逸速率的特性,阐明了随机共振信号的频率被限制在Kramers逃逸速率极限值一半的范围内,这种限制是制约大频率信号产生随机共振的原因.在进一步揭示二次采样随机共振频率尺度变换机理的基础上,证明了二次采样频率尺度可以把任意信号频率映射变换到随机共振频率尺度上的结论.相对于二次采样变换方法,由于双稳系统参数的调节很难使Kramers逃逸速率的一半达到实际信号的大频率,因此系统参数只能在随机共振的小参数频率范围内调节来实现随机共振. 关键词： 双稳随机共振 二次采样频率变换 系统参数调节 Kramers逃逸速率     

频域稀疏采样和激光成像方法

激光的单色性和自然图像频谱稀疏且集中在低频区间的特点,使图像频谱稀疏采样成像成为可能.基于小规模激光探测器,引入参考激光,本文提出了频域稀疏采样激光成像方法.介绍了频域稀疏采样激光成像的原理和成像系统结构,推导了激光回波重构复频谱的表达式,给出了重构频谱和复图像的仿真结果并分析了信号参数对重构效果的影响,同时采用相干系数、均方误差和结构相似度来评价其重构效果.规模为256×256的激光回波复图像仿真表明, 5个拼接1/4×1/4规模频域探测器组成的近似十字型稀疏采样结构,在约31.25%(5/16)的频域稀疏采样条件下,仍可获得较好的重构频谱和重构复图像.     

Optical noise reduction for dc-removed coaxial holographic data storage

A method of reconstructing positive and negative images from Fourier holograms recorded without the dc components is demonstrated by use of a coaxial holographic storage system. Reconstructed images are obtained by adding a phase-modulated dc component of the signal beam on reading. Contrast reversal of the reconstructed images can be achieved by reversing the readout reference pattern. This method can realize not only optical noise reduction but also less consumption of the dynamic range of the recording medium, potentially contributing to increasing the number of multiplexed holograms.     

A study of time over threshold (TOT) technique for plastic scintillator counter

A new charge measurement method, time over threshold (TOT), has been used in some gas detectors lately. Here TOT is studied for TOF system, made of plastic scintillator counter, which can simplify the electronics of the system. The signal characteristics are measured and analyzed with a high quality oscilloscope, including noise, pedestal, signal amplitude, total charge, rise time and the correlation between them. The TOT and charge are related and can be fitted by some empirical formula. The charge measurement resolution by TOT is given and this will help the design of TOF electronics.     

低能X射线工业CT小间隔信号采集系统

为克服探测器阵列获取速度慢、重建图像精度低的缺点,并能在低能X射线的小焦点/微焦点CT系统中完成对小型精密复杂器件的检测,研究了低能X射线工业CT的小间隔信号采集系统。系统选取DT公司0.2 mm像素尺寸、高集成度、扫描速度快的X-CARD 0.2-256G为探测器,Altera公司的Cyclone EP1C3T为主控芯片,Intel公司的LXT972A为以太网控制芯片。从数据传输的可靠、稳定、高效率角度出发,用模块化的方法给出了系统的硬件设计,用有限状态机技术完成了系统的逻辑单元设计,并对系统的动态范围进行了测试。测试实验结果表明,系统的动态范围大于4000,能够检测精密器件、准确迅速地完成信号的采集传输,满足实际工业CT对信号采集的要求。     

Gain-switched semiconductor laser amplifier as an ultrafast dynamical optical gate

A gain-switched semiconductor laser is shown to act as an optical gate with picosecond resolution and amplification for light pulses from another laser source. The amplification mechanism and the gate width change qualitatively when the gate laser undergoes a transition from a pumping rate slightly below the dynamic laser threshold to slightly above the dynamic threshold. If the gate laser is pumped below but close to its dynamical threshold, unsaturated amplification of an external signal pulse occurs over a delay time range between the external optical pulse and the electrical driving pulse of about 100–200 ps which is equivalent to the optical gate width. The signal amplification is observed to increase by two orders of magnitude and the gate width decreases by one order of magnitude if the gate laser is pumped slightly above the dynamical threshold. Amplification then occurs for input signals injected much earlier. A detailed theory of coherent, time-dependent amplification including the nonlinear dynamics of the semiconductor laser is shown to account for the observations. Both amplification regimes, below and above threshold, are reproduced in the numerical simulations. The extremely short and highly sensitive gate range above threshold is identified as being due to the gain maximum related with the first relaxation oscillation of the laser.     

Stochastic Resonance in Linear Region of a Single-Mode Laser： Effects of Amplitude Modulation of Signal

A single-mode laser noise model driven by quadratic colored pump noise and amplitude modulation signal is proposed. The real and imaginary parts of the pump noise are assumed to be cross-correlation. The effect of cross-correlation of noise and amplitude modulation of signal on laser statistical properties is studied by using the linearized approximation. The analytic expression of signal-to-noise ratio (SNR) is calculated. It is found that the phenomena of stochastic resonance (SR) respectively exist in the curves of the SNR versus the noise cross-correlation coefficient λ and the SNR versus the pump parameter a, as well as the SNR versus the signal frequency ω in our model. It is shown that there are three different typies of SR in the model: the conventional form of SR, the SR in the broad sense, and the bona fide SR.