用非线性理论阐述正弦反馈振荡器的频率和幅度稳定度

首先,本文对用于近似正弦反馈振荡器频率稳定度分析的线性理论作了简要的回顾然后应用描述函数法和判决方程法导出了非线性近似正弦反馈振荡器的振荡频率和振荡幅度稳定度的新的表达式。最后对导致用描述函数法和判决方程法导出的振荡频率稳定度不同的内在原因进行了详细的论述。     

以非线性理论阐述反馈振荡器的频率与幅度的稳定性

本文首先对线性的频率稳定理论用于近似正弦反馈振荡器的线性频率稳定理论,进行了评论性的回顾。在这方面,解释所谓的线性振荡器是清楚的。其后,是应用描述函数法和判决方程法所得到新的表达式,去阐述反馈振荡器考虑成一个非线性网络时的振荡频率和振荡幅度的稳定性。     

关于“激光振荡的半经典理论”的教学

通过建立“激光振荡的半经典理论”的图象,以场的自洽方程和原子体系的密度矩阵方程为主线索、省去繁杂的数学推导,建立引入各种假定的完备方程组。以场极化效应和量子体系的微扰作用为纽带,近似求解。使学生透过繁杂的公式了解频率索引、增益饱和、烧孔效应以及锁模机理等基本的激光现象和激光振荡的本质。     

兰姆激光半经典理论单模解的改进

本文从兰姆激光半经典理论中慢变复振幅极化强度一阶导数项不应忽略为出发点,对此理论做出了改进,得出了单模运转情况下新的激光自洽工作方程,并研究了反转粒子数变化以及极化场变化对场振幅与场位相的影响,以及反转阈值条件,牵引效应与排斥效应等。从而肯定兰姆理论中有关动态运转的理论与图示是错误的。笔者还发现当取腔模振荡频率等于二能级原子共振频率时,极化强度一     

H_2O,Ne分子填充对纳米碳管振荡器性能的影响

采用分子动力学方法,分别对管芯没有填充和填充了H2O或Ne分子的纳米碳管振荡器的振荡进行了模拟。根据计算结果,讨论了H2O或Ne分子填充对碳管振荡器振幅衰减、振荡频率等振荡性能的影响。研究表明,H2O或Ne分子的填充加速了振荡器振幅的衰减,其中,Ne填充振荡器的衰减最为严重,无填充碳管振荡器的振荡性能最好,Ne填充碳管振荡器的性能最差。     

CCCDTA的零-镜实现及其对正交振荡器综合的应用

为综合基于CCCDTA的正交振荡器,根据CCCDTA的端口关系,首次提出了CCCDTA的4个零-镜描述。借助已报道振荡器的NAME方程及其8个零-镜描述,实现2个基于CCCDTA的正交振荡器。通过调节2个CCCDTA的偏置电流,还能电控电路的振荡条件和振荡频率。作为一个例子,当振荡条件满足(IB2>IB1=260μA)时,实现了一个振荡频率为79.62 kHz的正交振荡器。计算机仿真证明所综合的电路正确有效。     

激光陀螺锁区影响因素分析

闭锁效应是激光陀螺的主要误差源.为了减小锁区阈值,本文基于激光陀螺的自洽方程组,推导了闭锁状态锁区阈值公式.通过MATLAB软件对三阶微扰下的lamb系数进行分析,研究了激光振荡频率、背向散射角和相对激发度对锁区阈值的影响.结果表明:腔长为0.28 m的激光陀螺,锁区阈值并不关于中心频率对称分布,也不严格随着背向散射角...     

核磁共振陀螺仪研究进展北大核心

核磁共振陀螺(NMRG)是基于量子原理的陀螺仪,具有高精度、体积小、抗干扰能力强等特点,是陀螺仪发展的重点方向之一。简要回顾了核磁共振陀螺的发展历史,介绍了20世纪有代表性的研究成果。叙述了核磁共振陀螺的基本工作原理和硬件系统构成。按照4种不同的技术路径:微型核磁共振陀螺、无自旋弛豫交换(SERF)核自旋陀螺、芯片级组合原子导航仪和基于金刚石氮空位的核磁共振陀螺,重点阐述近年来国外研究机构在核磁共振陀螺研究领域取得的最新成果,之后再介绍了近年来国内研究机构取得的主要研究成果。最后总结了核磁共振陀螺技术的最新发展趋势。     

晶体管反馈振荡器的频率稳定

振荡器的一项重要性能是振荡频率的稳定度,对电子管振荡器的频率稳定性能已有比较长时期的研究。然而,对晶体管振荡器频率稳定性能的研究则尚欠完善。本文将对晶体管反馈振荡器的频率稳定性能作比较详细的研讨。 根据四端网络分析及级联参数矩阵表示法,首先推导反馈振荡器的通用振荡方程,然后对共发射极网络的各种等效电路以及对各种纯电抗元件的反馈网络的级联参数进行分析,用这些网络形成各种晶体管反馈振荡器,并推导这些振荡器的振荡方程。根据振荡方程对这些振荡器的振荡性能,包括振荡频率的稳定性能,进行分析及比较。 假设反馈网络所用外加电抗元件固定不变,而晶体管参数改变(包括晶体管的输出输入电阻,输出输入电容,电流放大系数的虚数部分,负载电阻等的改变),对由于这些参数改变所引起的振荡频率漂移作了分析及比较。 根据所用反馈网络的几何构造,将反馈网络分成三臂π形,四臂及五臂网络等三类,对采用这三类网络而组成的晶体管振荡器的振荡性能进行分析,重要结果分别在三表中列出,供研究及设计者参考。     

激光腔内多模场的振荡特性分析

本文用半经典理论结构分析了激光腔内多模场与原子的相互作用，得到了腔内多模场的振幅和频率方程，并详细讨论了双模振荡的模式竞争情况。     

Self-consistency in the quasi-linear theory of electron cyclotron masers

The rate equation coefficients in the quasi-linear theory of the electron cyclotron maser are calculated self-consistently by using the true oscillator frequency. Theoretical corrections to the growth rate, oscillation frequency and saturation are calculated and compared with experiment. It is found that the self-consistency requirement can be met in a simple way which substantially improves the theory.     

RC oscillators with oscillation frequency independent of the op.-amp. gain-bandwidth product

Applying the determining equation proposed by Chua and Tang (1982), a frequency sensitivity problem in RC op.-amp. based oscillators is considered. A new expression for the sensitivity of oscillation frequency, ω_o, to changes in any oscillator parameter is developed. Then, the condition for this frequency to be insensitive to changes in the gain-bandwidth products (GB) of the op.-amp. used in the oscillator is formulated. Examples of two circuits exhibiting a zero sensitivity of ω_o to the GB changes (a very desirable feature) are presented. The first example represents oscillators with a single op.-amp. whose slew-rate effect is the only oscillator non-linearity. The second example concerns oscillators with a so-called composite amplifier where non-linear elements included in the oscillator feedback network are responsible for amplitude stabilization.     

DC instability of the series connection of tunneling diodes

An oscillator with a series connection of tunneling diodes produces significantly higher power than a single diode oscillator. However, a circuit with series-connected tunneling diodes biased simultaneously in the negative differential resistance (NDR) region of the I-V curve is dc unstable. This dc instability makes the series connection oscillator fundamentally different from a single diode oscillator. Associated with the dc instability are the phenomena of minimum oscillation amplitude and frequency. Due to the minimum oscillation amplitude, it is critical to provide the impedance match between the oscillator circuit and the series connection at the desired oscillation amplitude level. An in depth, comprehensive analysis of the dc instability is given here. Based on this analysis, a numerical procedure is developed to accurately predict the minimum oscillation amplitude and frequency. Time domain simulations which give further insight into series-connection oscillator behavior are discussed. The effect of increasing the number of diodes on the oscillator performance is explored as well. Based on numerical and simulation results, oscillators with several tunnel diodes connected in series were designed and tested. Experimental results that confirm the existence of the minimum oscillation amplitude are presented for oscillators with two, three, and four tunnel diodes     

A Stable Loss Control Feedback Loop for VCO Amplitude Tuning

In practical implementations of LC oscillators in which the quality factor of the tank is dominated by the quality factor of the inductor, due to dependence of the oscillation amplitude on the square of the oscillation frequency and the bias current of the LC tank, a stable amplitude control loop is essential to maintain a constant oscillation amplitude over the tuning range of the voltage-controlled oscillator (VCO) and to optimally bias the VCO over different conditions. In this paper, an enhanced loss control scheme incorporating an integral feedback to automatically tune the oscillation amplitude of LC oscillators is proposed. The proposed loss control feedback (LCF) loop is conditionally stable with an easy stability requirement to meet and its stability is examined: 1) by linearizing the system around the stable point using a perturbation method; and 2) by numerically solving the nonlinear differential equation of the LCF loop describing the transient behavior of the step response of the loop. A prototype including the LC VCO and the proposed LCF loop has been implemented in TSMC 0.35-mum CMOS process and occupies an area of 0.057 mm² and consumes 8.1 mA from a 2.8-V power supply. The LCF loop, with respect to the VCO, has an overhead of 25% on the area and consumes only 1.3% of the total power. Measurement results of the proposed LCF loop show an 11 dBm amplitude tuning range from -16 dBm to -5 dBm at any frequency over the 2-2.5-GHz tuning range of the VCO. The step response of the loop has a settling time less than 0.5 ns     

An AGC Circuit Design for a Variable-Frequency Sinusoidal Oscillator with Wide Frequency Range and Low Distortion Level

An up-down counter, multiplier, digital-to-analog (D/A) converter, and high-speed comparators are employed to achieve an automatic gain control (AGC) circuit, which corrects the pair of characteristic roots of the overall system automatically to the imaginary axis of the complex frequency plane. A negative feedback technique with digital hardware is applied on the loop gain control. No lowpass filter is needed to detect the oscillation amplitude. Thus, this technique is suitable for sinusoidal oscillators with a wide oscillation frequency range. Wien-bridge and phase-shift oscillators with an oscillation frequency range from 17 Hz to 1 MHz are tested with the proposed AGC circuit. The total harmonic distortions of the Wien-bridge sinusoidal oscillator with the proposed AGC circuit are verified to be very small. An application to a variable-frequency sinusoidal oscillator is also described. The experimental results demonstrate the static characteristics and dynamic responses of the overall system.     

Effects of hot-carrier stress on the performance of the LC-tank CMOS oscillators

The effects of hot carrier stress on a fully integrated negative resistance LC-tank CMOS oscillator are investigated. The major effect is the decrease of the amplitude of the oscillation due to degradation in the I-V characteristics of the MOSFETs. The oscillator phase noise increases with stress duration since the amplitude of the oscillation decreases. A change in the biasing of the circuit due to the stress affects the parasitic capacitances in the circuit which in turn cause a slight change in the oscillation frequency.     

Fluctuation characteristics of autodyne radars with frequency modulation

A mathematical model of the autodyne radar with frequency modulation has been developed. The model is presented in the form of a self-excited oscillator with single-loop oscillating system adjusted in terms of frequency by varying the varicap capacitance. This model takes into account the impact of intrinsic radiation reflected from the object of location and inherent noises of the generator, as well as the power source noises. Basic expressions were derived for the calculation of the signal accompanying the spurious response of generator, components of the legitimate signal and the noise during the registration of autodyne response both in the power supply circuit and in terms of the variation of oscillation amplitude. Calculations of noise characteristics were carried out at small and large values of the feedback parameter. The phenomenon of periodic nonstationarity of noise levels at the autodyne generator output was detected in conditions of strong feedback. The results of calculations and experiments were obtained for the autodyne built on an 8 mm-band Gunn diode.     

Amplitude Stabilized Transistorized Low Frequency Oscillator†

While generating very low frequency sinusoidal voltage, using operational amplifiers, one experiences difficulties in stabilizing the amplitude and every endeavour has been made to get a satisfactory solution. The paper describes one method by which stable oscillation can be obtained to a frequency as low as 0·01 c/s. The oscillator consists of two integrators and one sign changer interconnected in the form of a closed loop so as to solve a second-order differential equation. The amplitude is stabilized with the help of an extra stabilizing loop which consists of a squaring network. A brief analysis of the oscillator has been carried out and the precautions that have to be taken for improving the oscillator performance are discussed     

An optoelectronic self-oscillatory circuit with an optical fiber delayed feedback and its injection locking technique

An optoelectronic self-oscillatory circuit with a constant time delay and its injection locking have been theoretically and experimentally described. The oscillation circuit incorporates a delayed feedback path by utilizing an optical fiber and is characterized by a differential-difference equation. The oscillation waveform and amplitude have been investigated by computing the equation. It is also shown that a stable frequency locking region exists and expands with an increase in the injection amplitude. By employing a carrier signal, two methods for optoelectronic oscillation, an AM and an FM type, are proposed and have been demonstrated to obtain more stable oscillation.     

Stability of an Amorphous Silicon Oscillator

An RC oscillator using amorphous silicon thin film transistors was developed. The oscillation frequency and its dependence on resistance and bias voltage were studied. The frequency was controlled by adjusting the feedback resistance of the oscillator. The highest measured frequency of the oscillator was around 140 kHz, which is acceptable for low‐end radio frequency identification (RFID). Since a low‐end RFID circuit needs low cost and a simple process, an amorphous silicon oscillator is suitable.