Two-loop ternary adaptive delta modulation

A 2-loop ternary adaptive delta-modulation system is described which produces a peak s.n.r. of 20.5 dB, and for an s.n.r. of 15 dB, its dyamic range is 22dB when the input signal is RC shaped noise band limited to 2.5 kHz and the sampling rate is 8 kHz.     

Performance degradation of two-link binary c.p.s.k. system incorporating direct phase regenerator

The letter presents an analysis for the bit error probability (b.e.p.) of a two-link binary coherent phase-shift-keying (c.p.s.k.) system corrupted by additive Gaussian noise and consisting of a direct phase regenerator (d.p.r.) followed by a coherent receiver. Equivalent signal/noise ratio (s.n.r.) degradations due to imperfections in a practical d.p.r. are evaluated at the 10?6 b.e.p. point.     

Can a pulse excitation smaller than kT be detected?

A `1kT-pulse? excitation of a high-Q-factor LC ringing circuit is defined, and a filter configuration is described which allows the detection of such a pulse with good s.n.r. (signal/noise ratio) and excellent ?r, (resolving time). S.N.R.s considerably larger than unity were found experimentally, in reasonable agreement with theoretical calculations.     

Some results for an r.f.- and p.l.-modulated incoherent carrier

Possibilities of using incoherent carriers, amplitude-modulated by the message-modulated p.f.m., r.f.m. and p.l.m. have been investigated. It has been shown that, for noise bandwidths much smaller than the transmission bandwidth, efficient communication is possible, and s.n.r.s of 50?60dB are obtained for practical p.f.m.-a.m. and r.f.m.-a.m. systems. Some comparisons are also given.     

Performance of a differential coincidence-type self bit synchroniser at low s.n.r.

The behaviour of a differential coincidence-type self bit synchroniser at low s.n.r. has been examined for both uncorrelated and correlated input noise. It has been found that the performance of this synchroniser is comparable with that of a digital-data-transition tracking loop, and is better than that of an early-late-gate bit synchroniser.     

Quantitative analysis of 2-f.s.k. traffic detection

Two different methods of detecting signal flow in a noncoherent 2-f.s.k. channel are analysed with respect to the necessary signal/noise ratio for a certain error probability. It is found that separate detection of each frequency requires s.n.r. ?18 dB compared to about 19.5 dB for sum detection when the error probability is 10?7.     

Generation–recombination noise in bipolar transistors

The generation–recombination (g–r) noise in bipolar junction transistors (BJTs) is due to the deep-level impurities in the p–n junctions. The larger the amplitude of g–r noise, the worse the quality of BJTs, so that measuring the amplitude of the g–r noise is way of estimating the reliability of BJTs. In some papers, it is assumed that the amplitude of g–r noise is proportional to the square of base current (I_b²), but in a few papers it has been reported that this relation is more complex. In this paper the amplitude of g–r noise versus base current is discussed, the theoretical and experiment results demonstrate that the g–r noise and burst noise signal may be observed only in a certain range of base current, and the law S(f)∝I_b² is not valid. It means that we must measure g–r noise and observe burst noise signal over a wide range of base current to estimate the concentration of deep-level impurities in p–n junction and hence the reliability of BJTs.     

Zener-diode noise generators

Zener diodes operated in the breakdown region have been investigated as transfer noise standards in the r.f. region. A close correlation has been found between the variation in excess noise ratio (e.n.r., dB) and the temperature coefficient of Zener diodes. In particular, diodes having zero temperature coefficient of voltage also have zero temperature coefficient of e.n.r.     

噪声对消射频光子链路的噪声系数研究

噪声系数是宽带射频光子链路的重要参数,影响射频信号传输和处理系统的信噪比.提出了一种噪声对消射频光子链路,采用平衡光探测器对直流光和调制光转换的光电流相减处理,得到链路的噪声系数改善.从光信号调制、探测及噪声功率变化特性出发,建立了噪声对消射频光子链路的理论模型,并通过理论分析研究了噪声系数与激光功率、相对强度噪声、光...     

Analogue baseband TV transmission experiments using semiconductor laser diodes

The transmission characteristics of analogue video signals are investigated by using semiconductor laser diodes. It is shown that the linearity degradation due to speckle noise depends on the optical-fibre types adopted. Based on this investigation, transmission over 32 km is carried out by using a 1·3 ?m laser diode and single-mode fibres, with 46 dB unweighted s.n.r.     

几种相关双采样拓扑电路分析

相关双采样法在ＣＣＤ视频信号处理领域中被广泛使用,它不仅能有效地消除ＫＴＣ噪声,而且能够抑制低频噪声和宽带白噪声。文章对双δ法、四δ采样法（ＦＤＡ）、微分平均法、四δ法（ＦＧＡ）、双微分平均法五种相关双采样拓扑结构的电路进行研究,其中重点对双δ法的传输函数和抑制噪声能力进行了计算和分析。     

Effects of spacer thickness on noise performance of bipolar transistors

The effects of spacer thickness on noise performance of a bipolar junction transistor with different emitter widths and operation frequencies are examined. The minimum noise figure (NF/sub min/) derived from the Y-parameters as well as the base (r/sub B/) and emitter resistance (r/sub E/) obtained from the device simulation is used as a measure of noise characteristics. Furthermore, the noise resistance (R/sub n/), optimum source admittance (Y/sub sop/), and the associated gain (G/sub A,assc/) are also given in this brief. To achieve the minimum value of NF/sub min/, the spacer thickness should be targeted to an optimal value, and its value is frequency and geometry dependent.     

Interframe slope overload for television-picture noise reduction

Results of experiments on the temporal slope-overload phenomenon obtained with a 625 line/5.5 MHz digital television interframe delta modulator are reported. Whereas pictures containing genuine movement are heavily degraded, still pictures contaminated by noise can be rendered usable: s.n.r. improvements from 17 dB (original) to 34 dB (processed) have been obtained     

Noise-factor dependence on mismatch of low-level r.f. signal

The r.f. impedance (v.s.w.r.) and conversion loss of X band Schottky-barrier diodes were calculated from d.c. analysis. For a broadband case, it is found that diodes having a v.s.w.r. of 1.3?1.5 show a minimum conversion loss of 3.2 dB. These results are consistent with the experimental investigation, and show that matching a diode to the local-oscillator v.s.w.r. does not guarantee a correspondingly low conversion loss and low noise factor at the signal frequency. A matching to the low-level r.f. signal is required to obtain overall minimum conversion loss and noise figure.     

Characterization of generation–recombination noise using a physics-based device noise simulator

The implementation of generation–recombination (g–r) noise in a partial differential equation based device simulator is presented. Derived from the Shockley–Read–Hall model, the strength of each local g–r noise source is calculated based on the carrier transition rates between the conduction band, valence band, and trap states. The perturbations of these local g–r noise sources are then transmitted to the electrodes of the simulated device through scalar Green’s functions. g–r noise simulations are compared with existing measurements made on a four trap level, p-type silicon resistor. Good agreement between measured and simulated data is observed.     

Fluctuations in noise level

Consideration is given to the equations for the r.m.s. fluctuations of noise power, when the noise is random, is stationary and follows a Gaussian amplitude distribution. The results are briefly compared with published measurements, most of which show much larger fluctuations, both for white noise and 1/f noise.     

基于FPGA的数字图像中值滤波器设计

在电视跟踪系统中,为了抑制数字视频图像存在的脉冲噪声和满足系统实时性的需要,对图像进行基于硬件的实时滤波处理是有重要意义的。通过分析常见的3X3滤波窗口的数学模型,提出了基于FPOA的中值滤波算法及其设计方案。结合现场可编程门阵列FPOA的并行结构和适合流水线设计的结构特点,采用VHDL语言进行电路设计,利用仿真工具MODELSIM进行时序仿真验证。实际应用中表明可以滤除脉冲噪声,有效地改善了图像的质量,满足系统的实时性要求,提高了系统性能。     

Effect of laser phase noise in Sagnac interferometers

A theoretical analysis of the responsivity and the noise caused by backscattering in a Sagnac interferometer used as a sensor for reciprocal measurands, such as acoustic waves, is presented. Both Rayleigh backscattering and reflections from splices are taken into account. The noise power is found to increase proportionally to the source coherence time, and a noise equivalent phase shift in the range of 0.1×10^-6 rad r.m.s./Hz^1/2 is predicted for typical fibers and diode lasers. Experimentally, a noise equivalent phase shift of 2.5×10^-7 rad r.m.s./Hz^1/2 at 10 kHz was observed, with a detector current of 3 μA     

On the design of low-noise current-mode optical preamplifiers

Classical designs of optical transimpedance amplifiers for p-i-n photodiode receiver circuits generally employ common-emitter or common-source input stages. In this paper we explore the design of a new class of low-noise current-mode optical preamplifier based upon common-base and common-gate input stages. Two current-mode designs are considered, firstly an improved bipolar common-base configuration and secondly a GaAs MESFET common-gate configuration. Both designs employ current-feedback techniques to achieve higher transimpedance gains than is obtained with classical voltage-feedback structures for the same operating bandwidth. A theoretical noise analysis of the new current-mode designs confirms the expected low noise performance. Finally, experimental noise measurements at 100-MHz bandwidth indicates that under certain conditions electrical noise improvements of up to 4 dBs over classical designs can be obtained with the new current-mode circuits.     

全电视信号PCM编码色度副载波量化噪声的讨论

分析了全电视信号ＰＣＭ编码色度副载波量化噪声，并讨论了量化噪声与取样频率ｆｓ和量化比特数ｎ的关系。