锁相放大器直流输出分析——输入占空比可调矩形波信号

锁相放大器在微弱信号检测中具有广泛的应用,为了更好地了解锁相放大器的工作特性,采用占空比可调的矩形波信号作为信号源输入,系统研究锁相放大器的直流输出与输入信号的相位及占空比的关系。实验结果表明:采用幅值相同、不同占空比的矩形波信号通过锁相放大器其直流输出值不同,输入不同占空比的矩形波的被测信号在锁相放大器直流输出与相位和占空比的关系图像为三角波形,当占空比为0.5时有最大输出值。     

Photoelectric amplifiers F17

Conclusions The photoelectric amplifiers F17 have no electronic tubes, they are simple and reliable. Their output power is sufficient to work normal indicating and ink recording instruments. When this power is inadequate other amplifying devices can be connected to them (electronic, magnetic and other amplifiers including electric motors) thus providing any output power that may be required in practice. The zero drift in such cases remains, as it was originally insignificant.The F17 photoelectric amplifiers should extend the use of photocompensation systems to various spheres of science and technology.     

Wideband linear power amplifier for high-frequency ultrasonic coded excitation imaging

Linear power amplifiers are critical components in ultrasonic imaging systems that implement chirp-coded excitation. Bench-top commercial power amplifiers are usually used in academic laboratories for high-frequency ultrasound imaging, and the imaging performance depends greatly on these general-purpose instruments. To achieve a wide dynamic range, a power amplifier consisting of two stages is developed for chirp-coded ultrasound imaging applications through the implementation of custom-designed broadband 1:1 transformers and the optimization of feedback circuits. The amplifier has broad bandwidth (5 to 135 MHz), maintaining a linearity up to the 1-dB gain compression point (P1dB) of 41.5 dBm, allowing 16 dBm input power level at 60 MHz. The mean and the maximum values of output third-order intercept points (OIP3) are 51.8 and 53.5 dBm, respectively, between 20 and 110 MHz. With 12 dBm input power, the gain of the amplifier varies between 24 and 29 dB, offering a uniformity which would allow excitation of a 70-MHz single-element transducer with windowed chirp-coded bursts sweeping from 40 to 100 MHz. The performance in high-frequency ultrasound imaging is evaluated with a wire phantom. Echo signal-to-noise ratio (eSNR) of the designed amplifier is 7 dB better than a commercial amplifier, and spatial resolution is maintained.     

数显仪特征部分的误差分析

评价了数显仪特征部分误差分析方法,包括:采样/保持电路、模数转换单元的误差,并通过典型例子和列表数据分析了多种误差源及其综合计算方法.此外,还通过对现代动态范围内平均位误差风险因子量化(BERF)的评述,进一步探讨了传统意义上的数值化模拟系统与现代的建立在BERF-ε原理基础上的数显仪量化误差极限分析之间的关系.正因为后者建立在揭示噪声量子涨落性的直方图和量子相关性的功率谱密度测量上,所以能更客观地表征噪声的量子特性.     

Linearity and sensitivity of MIS position sensitive detectors

The linearity and sensitivity of linear Position Sensitive Detectors (PSD) are the two principal characteristics of sensors to be optimised in sensor fabrication. This work presents several efforts made to understand the internal and external parameters that influence the linearity and sensitivity of Metal Insulator Semiconductor (MIS) linear PSD with an active length of 6 cm. The use of long sensitive areas allows the PSD to achieve greater resolution without the need of a highly accurate light spot integration mechanism. The PSD is built in a multi-layered structure consisting of Cr/a-Si:H (n⁺ doped)/a-Si:H (intrinsic)/SiO_x (passivation layer)/Au, where the active a-Si:H layers were deposited by Modified Triode Plasma Enhanced Chemical Vapour Deposition (MTPECVD), which allows the deposition of good electronic grade material with a low (≈1 × 10¹⁵ cm^{− 3}) defect density inferred by CPM. The sensor linearity and sensitivity shows dependence on the sensor width to length ratio, SiO_x layer and on the value of the load resistance. Sensitivities of more than 30 mV/cm were achieved with linearity near 99%. Besides that, this type of MIS structure allows an improved spectral response in the near-UV region and has its maximum response at 540 nm.     

Absolute linearity measurements on a PbS detector in the infrared

The nonlinearity characteristics of a commercially available thin-film photoconductive PbS detector were experimentally investigated in the infrared using the National Physical Laboratory detector linearity characterization facility. The deviation from linearity of this detector was shown to be significant even for relatively low values of radiant power incident on the active area of the detector. For example, the linearity factor was approximately 0.8 when 0.6 microW of radiant power at a wavelength of 2.2 microm was illuminating a spot of 1 mm in diameter on the active area of the PbS detector. These figures demonstrate the poor linearity characteristics of this detector and provide a warning to other users of PbS detection systems. The deviation from linearity was shown to be a function of the size of the spot being illuminated on the detector active area, as well as the wavelength of the incident radiation. The deviation from linearity was shown to be a function of irradiance illuminating the detector for irradiance values lower than 1 microW mm(-2).     

Evaluation of neural network models with generalized sensitivity analysis

A sensitivity analysis method for discovering characteristic features of the input data using neural network classification models has been devised. The sensitivity is the gradient of the neural network model response function, and because neural network models are nonlinear, the gradient depends on the point where it is evaluated. Two criteria are used for measuring the sensitivity. The first criterion calculates the sensitivity or gradient of the neural network output with respect to the average of the objects that comprise each class. The second criterion measures the average sensitivity of the class objects. The sensitivity analysis was applied to temperature-constrained cascade correlation network models and evaluated with sets of synthetic data and experimental mobility spectra. The neural network models were built using temperature-constrained cascade correlation networks (TCCCNs). A weight constraint was devised for the output units of the network models. This method implements weight decay with conjugate gradient training and yields more sensitive neural network models. Temperature-constrained hidden units furnish more sensitive network models than networks without constraints. By comparing the sensitivities of the class mean input and the mean sensitivity for all the inputs of a class, the individual input variables may be assessed for linearity. If these two sensitivities for an input variable differ by a constant factor, then that variable is modeled by a simple linear relationship. If the two sensitivities vary by a nonconstant scale factor, then the variable is modeled by higher order functions in the network. The sensitivity method was used to diagnose errors in the training data, and the test for linearity indicated a TCCCN architecture that had better predictability.     

Frequency Modulation Multiplexing for Simultaneous Detection of Multiple Gases by use of Wavelength Modulation Spectroscopy with Diode Lasers

Modulation frequency multiplexing provides a straightforward method, analogous to television or radio broadcasting, for performing simultaneous detection of multiple gases by use of wavelength modulation spectroscopy with diode lasers. When fiber-optic coupled lasers are used, our approach guarantees that all beams transit the same optical path and impinge on the same detector. Each laser is modulated at a different frequency and the detector output is processed by a set of lock-in amplifiers, one for each laser, to measure the absorbance encountered by each laser.     

Absolute linearity measurements on LiTaO3 pyroelectric detectors

The nonlinearity characteristics of a number of LiTaO3 pyroelectric detectors were experimentally investigated using the National Physical Laboratory (NPL) detector linearity characterization facility. All the detectors examined were shown to exhibit a superlinear response, i.e., the responsivity of the detectors increases as the incident radiant power increases. The temperature coefficient of response of some of these LiTaO3 pyroelectric detectors was measured and found to be approximately +0.2% degrees C(-1). The superlinear behavior of the LiTaO3 pyroelectric detectors was attributed to the positive temperature coefficient of response values of these detectors. Moreover, the linearity factor of gold-black-coated LiTaO3 pyroelectric detectors was shown to exhibit a dependency on the area of the spot illuminating the active area of the detector, i.e., on the incident irradiance. Possible reasons for the observed behavior are proposed and discussed. Some variations in the slopes of the plots of the linearity factor versus irradiance for different areas being illuminated have been assigned to the poor spatial uniformity of response of these detectors.     

Absolute linearity measurements on HgCdTe detectors in the infrared region

The nonlinearity characteristics of photoconductive and photovoltaic HgCdTe detectors were experimentally investigated in the infrared wavelength region by use of the National Physical Laboratory detector linearity measurement facility. The nonlinearity of photoconductive HgCdTe detectors was shown to be a function of irradiance rather than the total radiant power incident on the detector. Photoconductive HgCdTe detectors supplied by different vendors were shown to have similar linearity characteristics for wavelengths around 10 microm. However, the nonlinearity of response of a photovoltaic HgCdTe detector was shown to be significantly lower than the corresponding value for photoconductive HgCdTe detectors at the same wavelength.     

Long-optical-path scanning mechanism for optical coherence tomography

A new scanning mechanism for changing long optical paths is proposed. This mechanism consists of corner reflectors arranged equally upon a disk and an outer mirror. Rotating the 120-mm disk causes a long-optical-path change in each reflector with a near linearity of more than 40 mm. An optical coherence tomography system is described that confirms the usefulness of the proposed mechanism. Its operating characteristics and accuracy are evaluated by analysis and experiment. The deviation of the optical-path change is less than 1.52% at a reflector rotation angle of +/-10 degrees. A high-speed lock-in amplifier is utilized for fundamental measurements of glass samples.     

时间序列线性／非线性在线检验

给出了ＡＲ模型参数二阶矩Ｙｕｌｅ－Ｗａｌｋｅｒ方程和四阶矩Ｙｕｌｅ－Ｗａｌｋｅｒ方程估计的等价最小二乘估计，以及二阶矩和四阶矩Ｙｕｌｅ－Ｗａｌｋｅｒ方程参数估计的递推算法，在此基础上提出一种时间序列的线性／非线性在线检验方法。     

基于PSD的强背景下光点位置探测技术研究

目前基于PSD的光电探测应用大多是以激光入射,有效信号远强于背景,为了满足更大的测量需求,本文提出了一种基于PSD的强背景下探测闪光点空间位置的方法.设计了预处理电路将PSD产生的微弱电流信号转换为电压信号并经过高速AD转换为数字信号,分析了背景信号对PSD测量结果的影响,提出了在软件中减去背景和暗电流以提取有效信号并对其进行精确计算的方法.用LED做闪光点在不同室外背景下进行了相关实验,结果表明:该方法可以实现200 kHz的高速测量,有效去除了不同背景和暗电流的影响,强背景下测量线性误差在±1.2％以内.     

新型光纤电流传感器的研制

光纤电流传感器运用Faraday效应,将光纤绕在电流母线上可以方便地测得电流母线中的电流,但光纤电流传感器的信号受环境振动、温度变化的影响严重,从而限制了其应用。本文从分析振动、温度变化的干扰机理出发,提出一种新型的在线校正方法来抑制干扰的影响,并进行了原理性实验。研究结果表明,用这种方法实现的光纤电流传感器在40～400A之间有良好的线性度和精度。     

Real-time digital control of optical interferometers by the mechanical-modulation technique

We discuss the application of digital systems to the automatic control of dual-wave optical interferometers. We show that, if the mechanical-modulation technique is used for error-signal extraction, digital techniques can be used both for error-signal extraction and for control-signal generation. Therefore, apart from two front/end amplifiers that are necessary to match the dynamics of the detectors and actuators to the dynamics of the analog-to-digital converters and digital-to-analog converters, no other analog devices are required. In particular, the mechanical-modulation technique requires the synchronous demodulation of the photodiode output signal. Hence we need to implement a digital lock-in amplifier whose algorithm is described here. Finally, we describe one of the possible applications of this digital control procedure, such as the control of a classic Mach-Zehnder interferometer in air.     

Small-angle measurement by use of a single prism

A new method of angle measurement based on the internal reflection effect is proposed that uses a single right-angle prism. We measure the angular displacement between a laser beam and the prism by detecting the changes in reflectance as a function of the angle of incidence. We achieve high linearity of measurement by taking the inverse of reflectance as the output. The inverse of reflectance is obtained from the intensities of the reflected and the transmitted beams measured by two photodiodes. Experiments with a prototype device have demonstrated that angle measurement with a range of ?500 arc sec, a nonlinearity error of ?0.1%, and a resolution of 0.1 arc sec can be readily achieved. The measurement range can be further increased with some sacrifice of linearity.     

Total internal reflection for precision small-angle measurement

A method for precision small-angle measurement is proposed. This method is based on the total-internal-reflection effect of a light beam at a pair of glass prisms. Angular displacement of the light beam is measured when the intensity change of the reflected beam is detected as a result of the relative phase shift between the s- and the p-polarized beams. An initial phase shift between the s- and the p-polarized components is introduced to increase measurement sensitivity. For increased measurement linearity and reduced effect of laser power fluctuation on the output, a differential method is used in which the light beam is split equally into two beams, each reflected at a prism and detected by a photodiode. The output is obtained as the difference of the two detected intensities divided by their sum. A prototype device was built, which demonstrated a nonlinearity error of 1.3% in a measurement range of ?0.6 degrees or 0.4% in ?0.3 degrees . The peak-to-peak noise level was found to be at approximately 0.5 arc sec. This noise level can be reduced further and resolution increased by a reduction of the measurement range.     

Neutral loss analysis in MALDI-MS using an ion-gate scanning mode.

Matrix-assisted laser desorption/ionization reflector time-of-flight (MALDI-reTOF) and electrospray ionization (ESI) mass spectrometry (MS) have become essential tools for the characterization of peptides and proteins. Whereas ESI in combination with a triple quadrupole analyzer allows product ion, precursor ion, and neutral loss analyses, MALDI-reTOF instruments can only be used to record product ion spectra based on the in-source or postsource decay (PSD). We describe a new method to perform neutral loss analyses in MALDI-reTOF instruments in a manner that identifies posttranslationally modified peptides and furthermore retrieves sequence information from peptides. The method is based on the selection of ions in a small time interval to record only signals within the corresponding mass interval. By stepping the time interval through the complete mass range, we obtained a spectrum of stable ions by combining the signals of all individually recorded time intervals. This method furthermore permits PSD fragment ions to be identified, since they reach the detector earlier than the stable ions transmitted in the chosen time interval. The neutral loss analysis were calculated by correlating the PSD fragment ions to the corresponding parent ion detected in this time interval. Moreover, this MALDI-MS mode increased the number of detectable signals in complex peptide mixtures and the signal-to-noise ratio.     

Quantum amplifiers at microwave frequencies using Josephson junctions

Abstract

Josephson junctions are quantum mechanical devices with sinusoidal nonlinearity and their use as amplifiers of non-classical microwaves in cavities at low temperatures, is discussed. Self-pumped amplifiers as well as externally pumped three- and four-photon amplifiers are considered, and a quantum theory that describes their operation is developed. It is shown that the sinusoidal nonlinearity can be expanded into a series of terms, the first few of which are familiar from quantum optical amplifiers that use nonlinear optical materials, while the others are higher order corrections.     

A method for measurement of multiple light spot positions on oneposition-sensitive detector (PSD)

The measurement method described relies on using light sources, each of which is modulated at different frequencies and then demodulated in the sensor signal-processing circuit using a pulse amplitude modulation (PAM) scheme. The position of each light spot can be determined even if there are other beams irradiating the PSD at the same time. In a very simple experiment, the light beams from two LEDs were projected onto one PSD, with one LED modulated at 10 kHz and the other at 5 kHz. The PSD was calibrated by scanning the light beams across the PSD in equidistant grid lines over a 4-mm×7.2-mm area. It was found that the resolution, linearity, and accuracy of the measurement are not affected even if multiple light beams are continuously present. The number of light beams which can be used simultaneously is limited only by the bandwidth of the PSD and the sampling time of the sample/hold devices used in the DC restoration circuit