Reset noise reduction in capacitive sensors

Reset noise sets a fundamental detection limit on capacitive sensors. Many sensing circuits depend on accumulating charge on a capacitor as the sensing method. Reset noise is the noise that occurs when the capacitor is reset prior to the charge accumulation cycle. Therefore, it is important to understand the factors which determine reset noise, and how this noise may be mitigated. The purpose of this paper is to show how capacitive reset noise can be reduced during the reset cycle. We present and analyze three circuits that implement the basic methods for directly reducing capacitive reset noise. In addition, we present a time-domain technique for analyzing the time-varying statistics of these circuits. This technique makes use of Ito/spl circ/ calculus to obtain solutions to the time-varying stochastic differential equations. Theoretical noise calculations and Monte Carlo simulation results are presented for each technique. We show that theory and simulation yield similar results. Finally, we show in the examples that reset noise may be reduced by a factor of 20 or more. We also refer to implemented sensor arrays which achieve these results.     

Tanlock loop noise reduction using an optimised phase detector

This article proposes a time-delay digital tanlock loop (TDTL), which uses a new phase detector (PD) design that is optimised for noise reduction making it amenable for applications that require wide lock range without sacrificing the level of noise immunity. The proposed system uses an improved phase detector design which uses two phase detectors; one PD is used to optimise the noise immunity whilst the other is used to control the acquisition time of the TDTL system. Using the modified phase detector it is possible to reduce the second- and higher-order harmonics by at least 50% compared with the conventional TDTL system. The proposed system was simulated and tested using MATLAB/Simulink using frequency step inputs and inputs corrupted with varying levels of harmonic distortion. A hardware prototype of the system was implemented using a field programmable gate array (FPGA). The practical and simulation results indicate considerable improvement in the noise performance of the proposed system over the conventional TDTL architecture.     

Interferometric noise reduction in fiber-optic links bysuperposition of high frequency modulation

The reduction of interferometric noise by superposition of high frequency modulation is analyzed. It is shown that the nature of this reduction is due to a redistribution of noise energy from baseband to higher frequencies where it can be discarded by low-pass filtering. Detailed analysis revealed the dependence of the noise reduction factor on the product f_0τ, and the modulation index of the high frequency superimposed modulation. The proper choice of parameters can lead to complete elimination of the converted phase noise from the system     

光纤传感器的研究及应用

介绍了光纤传感器与其他传感器相比的优点,还介绍了传感型光纤传感器与传光型光纤传感器的基本原理.同时,文章阐述了强度调制型光纤传感器、干涉型光纤传感器、光纤光栅和光纤声发射传感器的应用.文章最后提出了我国光纤传感技术存在的问题以及发展方向.     

Demodulation of interferometric sensors using a fiber-optic passive quadrature demodulator

The passive quadrature demodulator (PQD) eliminates the phase stretcher and feedback electronics frequently used in fiber interferometric sensors by passively extracting the desired signal using two distinct interferometers which differ in phase bypi/2. A fusion technique is described to fabricate a fiber PQD which is sufficiently stable with respect to temperature, polarization, and wavelength to maintain the sensitivity of interferometric sensors constant to 0.25 dB.     

Wide-frequency fiber-optic phase modulator using piezoelectricpolymer coating

The highly sensitive response of a fiber-optic phase modulator that is coated with 80-90-μm-thick vinylidene fluoride/trifluoroethylene copolymer on an 80-μm-diameter single-mode fiber and made piezoactive by radial poling is demonstrated over a wide frequency range, from 500 Hz to 50 MHz. In the range of 10 kHz up to 2 MHz, a relatively flat response is measured, whereas at high frequencies between 6 and 50 MHz, the phase modulation exhibits multiple peaks dominated by radial resonances of the fiber-jacket composite. Theoretical considerations on the phase shift and experimental results are given     

Compensation of phase noise in OFDM systems using an ICI reduction scheme

In Orthogonal Frequency Division Multiplexing (OFDM) communication systems, the local oscillator phase noise introduces two effects: common phase error (CPE) and inter-carrier interference (ICI). The correction of CPE does not suffice always, especially when high data rates are required. Through the creation of a frequency-domain linearized parametric model for phase noise, we generate an ICI reduction scheme to deal with phase noise. The effects of the transmitter high-power-amplifier (HPA) nonlinearity on the phase noise compensation are also investigated. The algorithm performance over AWGN channel is presented for DVB-T 2k and 8k modes. It is shown by the simulation results that the algorithm can significantly reduce the symbol-error rate (SER) floor, caused by the residual phase noise after CPE correction, while sacrificing an acceptable transmission bandwidth.     

Analysis of optical phase noise in fiber-optic systems employing a laser source with arbitrary coherence time

Performance of many optical circuits and systems, such as signal processing and sensing devices, is influenced by random fluctuations of the optical source emission field. This paper outlines a formalism for the analysis of laser phase noise effects on a general linear time-invariant optical system. Theoretical expressions are presented for the autocovariance function of the instantaneous output intensity which are valid for any source coherence time as long as the source intensity fluctuations are assumed to be negligible. Applications of the results to some fiber-optic systems such as Mach-Zehnder and recirculating delay line devices also are demonstrated, both in the coherent and incoherent regimes. Although the analysis is not limited just to fiber-optical systems, our attention is focused on fiber optics.     

A phase noise reduction technique in microwave oscillator using high-Q active filter

The authors present a 10 GHz oscillator that uses a high-Q active filter to reduce the phase noise. The loaded Q of active filter is obtained at about 500. This oscillator is compared with another oscillator which uses a passive filter. The difference of two oscillators' Q is estimated at 12.5 times the open-loop gain simulation. The measured result of phase noise at 100 kHz offset shows maximum 10 dB reduction with high-Q active filter.     

Multiplexing of nonlinear fiber-optic interferometric sensors

The scheme is demonstrated with a three-sensor array consisting of magnetic-field, pressure, and displacement sensors exhibiting resolutions at 1 Hz of 20 μOe/√Hz (limited by ambient noise), 0.1 kPa/√Hz, and 30 nm/√Hz, respectively. Multiplexing is accomplished by dithering each transducer at a different frequency and using parallel phase-sensitive detectors (PSD) at the interferometer output to demultiplex the information. A single Mach-Zehnder interferometer driven by a single unmodulated laser was used. Factors affecting the performance of the multiplexing scheme, including interferometric demodulation technique, PSD performance, and nonlinear transduction mechanism, are discussed     

Historical review of microbend fiber-optic sensors

This paper traces microbend sensors from the early investigative work into initial applications to measure many different parameters, through advanced prototype development and commercial hardware. Advantages and disadvantages of microbend sensors are discussed     

Coherence multiplexing of fiber-optic interferometric sensors

This paper describes a method of multiplexing several optical signals onto a single spatial channel (e.g., a single-mode fiber) using a short coherence length continuous wave light source. Several system configurations which utilize this technique are proposed, and some design considerations are discussed. Experimental results for a single sensor and receiver are presented and compared with theoretical predictions.     

Linearity stablized fiber-optic thermometer using pseudo-heterodyne phase detection

A temperature sensor using a fiber-optic Fabry-Perot interferometer is described. A pseudo-heterodyne detection scheme is adopted to read the light phase difference in the Fabry-Perot interference output. A higher harmonic components comparison method is used to stabilize the system and to increase detection linearity. This system realizes not only highly sensitive temperature sensing with good linearity and minimal adjusting error, but also application to the sensing of other physical quantities such as vibrations. Additionally, the signal-to-noise ratio and distortion of the detected signal are investigated as functions of fiber end reflectivity. These results will be useful in designing a high performance fiber-optic Fabry-Perot thermometer.     

Dual-loop integer PLL for phase noise reduction

Analog Integrated Circuits and Signal Processing - In this work, a dual-loop integer PLL is proposed aimed at improving the overall phase noise performance at the PLL output. The main loop is a...     

Sideband noise of a large phase carrier in interferometric sensors

Interferometric sensors using balanced detectors and phase stabilisation schemes remain susceptible to laser intensity noise if phase carrier techniques are employed. An intensity stability of 4 × 10?6 is required for the low-frequency side-band noise to be equivalent to microradian phase shift sensitivity if the phase carrier has a peak phase shift of ?/2 rad.     

Signal-induced noise in fiber-optic links using directly modulatedFabry-Perot and distributed-feedback laser diodes

A quantitative comparison has been made, both theoretically and experimentally, of signal-induced noise in high-frequency, single-mode fiber-optic links using directly modulated multimode (Fabry-Perot) and single-frequency (distributed-feedback, DFB) lasers. It is shown that the common procedure of evaluating the signal-to-noise (S/N) performance in a typical fiber-optic link by treating the various sources of noise as additive quantities that are independent of the modulation signal is inadequate. This is due to the presence of signal-induced noise, which concentrates at low frequencies, so that a casual observation might lead to the erroneous conclusion that it is of no relevance to high-frequency transmission systems. It is shown that, for Fabry-Perot lasers, signal-induced noise arising from translation of low-frequency noise to high frequencies causes significant degradation in S/N performance in transmission of 6-GHz signals over only 1 km of single-mode fiber. With DFB lasers, signal-induced noise due to interferometric phase arrow intensity conversion is present, but does not become significant even for transmission at 10 GHz up to 20 km     

基于OTDR的螺旋型分布式光纤传感器的研究

对基于光时域反射仪(OTDR)的螺旋型分布式光纤传感器的工作机理进行了分析,通过试验获得了光纤宏弯曲损耗-位移的拟合曲线,以及该曲线与工作波长、棒体直径的关系.研究结果表明:该螺旋型分布式光纤传感器具有监测量程大、定位精度高的特点,通过优化工作波长和棒体尺寸,可以进一步提高传感器的量程和性能.     

Reset noise reduction through column-level feedback reset in CMOS image sensors

A low reset noise CMOS image sensor(CIS) based on column-level feedback reset is proposed.A feedback loop was formed through an amplifier and a switch.A prototype CMOS image sensor was developed with a 0.18μm CIS process.Through matching the noise bandwidth and the bandwidth of the amplifier,with the falling time period of the reset impulse 6μs,experimental results show the reset noise level can experience up to 25 dB reduction.The proposed CMOS image sensor meets the demand of applications in high speed security surveillance systems,especially in low illumination.     

Oscillator stability and phase noise reduction in phase lockedactive microstrip patch antenna

A phase locked loop (PLL) method for controlling a 4 GHz active patch antenna was investigated in order to both frequency stabilise the oscillator and to reduce the phase noise; both these aims were achieved by optimising the PLL parameters. Experimental results showed that a phase noise reduction of up to 26 dB was realised     

列级反馈降低复位噪声的CMOS图像传感器

提出了一种通过放大器和开关建立起反馈环路,基于列级反馈复位的低噪声CMOS图像传感器（CIS）。设计的CMOS图像传感器采用0.18μm CIS工艺进行了流片,测试结果表明,通过对噪声带宽与反馈放大器的带宽匹配,在复位脉冲下降沿时间为6µs的条件下,传感器的复位噪声减少25dB,满足低照度高速的安防监视系统的应用需求。