马赫曾德尔调制器偏压控制技术研究

介绍了马赫曾德尔调制器的工作原理及传输曲线随温度漂移引起偏置工作点改变的现象。理论推导出基于谐波分析的马赫曾德尔调制器偏压工作点稳定控制方法,同时通过导频信号来度量偏压工作点的漂移量。设计出基于FPAG的马赫曾德尔调制器偏压控制硬件模块,通过记录接入该模块前后PIN光电二极管电压及马赫曾德尔调制器输出光功率的变化情况,最终证实该偏压控制模块可以实现稳定马赫曾德尔调制器工作点的目的。     

马赫-曾德尔电光调制器工作点自动控制

为实现马赫-曾德尔(MZ)电光强度调制器(EOIM)工作点的实时控制,提出一种基于虚拟仪器技术的工作点自动控制方案。采用闭环反馈控制系统,引入微扰动信号,通过"扫描—鉴相补偿"的方法,可以使自动控制工作点长时间锁定于传输曲线的最低点。当激光器输出功率为6mW,控制EOIM在1h内稳定于最低点,实验测得EOIM输出平均光功率1.198μW,标准差0.123μW,波动小于0.43μW;在EOIM最低点外加电脉冲信号进行调制时,产生消光比均值达25.71dB的光脉冲。输出脉冲消光比与未加控制时相比提高9.94dB,波动小于0.5dB,大大提高了MZ电光调制器的工作稳定性。     

超宽带脉冲形状调制技术

基于调制器的电光效应,提出一种并联式LiNbO3马赫-曾德尔调制器结构实现超宽带(UWB)脉冲形状调制(PSM)的方案。利用软件Optisystem7.0模拟实验环境,观察和分析不同环境下输出调制信号的性能,并研究输出的PSM信号在光纤中的传输特性。     

电光调制器偏置点抖动控制对射频信号的影响

马赫-曾德尔电光调制器的偏置点控制是光载射频传输链路中一项十分关键的技术。为了分析马赫-曾德尔电光调制器偏置点抖动控制对射频信号的影响,用贝塞尔级数展开再进行频谱分析的方法对系统输出信号成分进行了理论分析,设计了马赫-曾德尔调制器任意点控制系统并进行了实验验证。用MATLAB进行仿真后可知,在输入射频功率为18dBm时,抖动信号幅度需小于45mV,2次射频信号对抖动信号引起的频率分量抑制比才能大于20dB;而在输入射频功率为10dBm时,这个幅度要小于19mV。改变抖动信号幅度进行实验,得到2次射频信号对抖动信号引起的频率分量抑制比与仿真结果误差始终保持在3dB~3.2dB左右。结果表明,马赫-曾德尔电光调制器工作在线性偏置点时,抖动信号引起的频率分量是可以忽略的;但将调制器偏置控制在最低偏置点时,对射频信号的影响不可忽略。     

功率和谐波同步检测的马赫曾德调制器偏压控制技术

为了克服马赫曾德调制器工作点随温度、压力等外界因素的漂移,需要对它的直流偏压进行补偿。以往采用微扰信号谐波检测的方案偏置点定位精度高,但由于需要在回路中附加小幅抖动信号,会引入一定的噪声,影响信号的纯度;而功率检测的方案易受光源功率自身扰动的影响,稳定性不高,且偏置点定位性能差。提出了一种平均功率和谐波检测相结合的MZ调制器偏置点控制技术,通过谐波探测确定最佳工作点,并以电光调制器前后光功率比值作为基准值进行反馈控制,提高了偏压控制的定位精度和噪声性能,同时克服了激光功率自身扰动的影响。在此过程中还提出了一种通过操控误差信号实现偏置点任意调节的方案,实现了大范围灵活的偏置点控制。实验发现,所提出的方案具有定位精度高、稳定性好和偏置点调节范围广的优点,能够很好地满足马赫曾德调制器偏置点控制的要求。     

基于级联马赫-曾德尔调制器的太赫兹通信系统

为了有效解决太赫兹通信系统中信号难以调制,影响通信系统性能的问题,提出了一种基于级联马赫-曾德尔调制器的太赫兹通信系统。将要传递的伪随机不归零码与频率为10GHz的射频本振信号混频后调制到级联马赫-曾德尔调制器上,通过调节两个调制器的偏置电压,使其分别偏置在最大传输点和最小传输点上,得到的光载波信号经过光放大器放大,结合高非线性光纤的四波混频效应,利用相移布喇格光栅进行模式选择,经过光电转换后的太赫兹信号通过基带数据恢复,可以得出该太赫兹通信系统传输的误比特率。结果表明,基于级联马赫-曾德尔调制器结构可以将太赫兹信号的产生与调制结合到一起。该研究对太赫兹通信系统的实用化有一定借鉴意义。     

电光双向强度调制器的隔离度研究

设计和制作了应用于微波全双工收发系统的马赫-曾德尔型电光双向强度调制器。根据电光调制器中电信号对光信号的调制叠加原理,通过计算和仿真,分析了因调制电极设计电场与实际电场分布差异导致的器件隔离度劣化。通过对比不同调制电极结构的分析设计和仿真优化结果,得到3.5GHz以上频段隔离度优于-30dB的电光双向强度调制器设计结构。制备出的电光双向强度调制器在5~17GHz范围内隔离度优于-30dB。     

基于MZ调制器工作点控制的前端电路设计

设计了马赫-曾德尔(MZ)调制器工作点控制的前端电路.利用运放OP27设计文氏桥电路,产生1 kHz余弦波,作为扰动信号加到MZ调制器的RF端.运用运放OP27设计带通滤波器,从探测器分别提取一次谐波和二次谐波.利用乘法器MLT04实现对一次谐波和二次谐波的检波,分别得到一次谐波的幅度调制信号和二次谐波的幅度调制信号.这两个调制信号含有调制器工作点的相位信息,为后续的软件控制提供了两路含有相位信息的信号,使整个控制系统的实现更准确.     

基于并联DPMZM的大动态范围微波光子混频系统

为了解决微波光子混频系统的非线性失真和动态范围受限问题,提出了一种基于并联双平行马赫-曾德尔调制器(DPMZM)的大动态范围微波光子混频系统。利用DPMZM实现射频和本振信号的并行调制,通过配置并行两路的电光调制指数及调制器的工作点,抵消输出中频信号中的三阶交调失真(IMD3),最终提高系统的动态范围。仿真结果表明,所提方案可将IMD3抑制17.7 dB,系统无杂散动态范围提高到127.8 dB·Hz 4/5。     

基于级联调制器的24倍频毫米波信号产生

为了有效解决高频毫米波信号源产生困难的问题,提出了一种基于级联强度调制器的24倍频可调毫米波信号产生系统.将低频本振信号调制到第一级双平行马赫-曾德尔强度调制器上,分别控制主调制器和子调制器的偏置电压,使其均偏置在最大传输点上,精确控制低频本振信号的幅值和相位,可以对应产生的-4阶和+4阶边带信号,通过光电检测器拍频,得到的8倍频信号调制到第二级马赫-曾德尔调制器上,控制第二级调制器的偏置电压,使其工作在最小传输点上,可以产生-12阶和+12阶边带信号,经过光电转换后可以得到射频驱动信号频率24倍的毫米波信号,当本振信号频率发生改变时,得到的毫米波信号频率对应改变.     

一种基于MZM的电信号任意倍频方法

文章提出一种使用马赫-曾德尔强度调制器(MZM)产生输入信号的任意倍频信号的方案,利用该方法不仅可以产生输入信号的偶数倍倍频信号,还可以产生输入信号的奇数倍信号.通过设置马赫-曾德尔强度调制器的直流偏置点在线性偏置点,产生了奇数倍信号,通过设置直流偏置点在特殊的非线性偏置点,产生了偶数倍信号.通过调节输入信号的幅度,可以得到想要的高阶倍频信号.理论分析和实验证实了该方案的可行性.     

A third-order sigma-delta modulator with extended dynamic range

Oversampling modulators based on high-order sigma-delta modulation provide an effective means of achieving high-resolution analog-to-digital conversion in VLSI technology. Because high-order noise shaping greatly reduces the quantization noise in the signal band, the dynamic range of these modulators tends to be bounded by the thermal noise of the input stage and the maximum voltage swing in the signal path. This paper introduces a third-order cascaded sigma-delta modulator that uses a modified cascaded architecture and reduced gain in the first integrator to increase the dynamic range. An experimental modulator fabricated in a 1-μm CMOS technology attains a resolution of 17 b for a 25-kHz signal bandwidth while operating from a single 5-V supply. With an oversampling ratio of 128 and a clock frequency of 6.4 MHz, the modulator achieves a 104-dB dynamic range and a peak signal-to-noise+distortion ratio (SNDR) of 98 dB. As indicated by both measurements and simulations, the cascaded architecture also greatly reduces the discrete noise peaks that can be present in a single-stage architecture     

高阶Sigma-delta调制器传递函数设计方法

文章在Richard Schreier的Matlab Sigma-delta调制器设计工具包的基础上，提出了一种新的稳定的高阶调制器传递函数设计方法．给出了详细的设计步骤。通过这种方法可以确定在最大输入范围下的稳定调制器的噪声传递函数，作为设计实例，对不同过采样率，不同阶数和不同量化器位数组合下调制器的传递函数进行了分析，并将结果以表格的形式给出，可以作为设计参考。     

Low cost wideband I-Q vector modulator

One of the applications of QPSK modulators is to control the amplitude and phase of an RF signal, working as a vector modulator. Recently there are several monolithic commercial circuits that can be easily used to frequencies of >4 GHz. First, the input signal must be decomposed into two quadrature components, which is usually done in a 3 dB 90° hybrid coupler. Using microstrip techniques, this I-Q vector modulator exhibits narrowband characteristics, due to the degradation of the hybrid performances with frequency. The authors show how the working bandwidth can be extended up to an octave by means of a versatile control system as described here, as an alternative to a new design of the RF stage     

Numerical method for determining the quantization error PDF of single-bit /spl Sigma//spl Delta/ Modulators

Existing models for the quantizer of /spl Sigma//spl Delta/ modulators make assumptions on the probability density function (pdf) of the quantization error, or some other convenient signal of the modulator. In this paper, a method for the determination of this pdf for single-bit /spl Sigma//spl Delta/ modulators is presented. First, a numerical method is proposed in order to solve the simplified equation for the quantization error pdf for first-order systems considering noiseless and noisy dc input signals. Then, it is shown how most practical high-order (>2)/spl Sigma//spl Delta/ modulators, resulting from well-established design methods, can be modeled as first-order systems plus an additive noise source at the input. Hence, their quantization error pdf is analyzed using the proposed method. Simulation results are shown to be in considerable agreement with those of the proposed method.     

Detailed analysis of the effect of a hysteretic quantizer in a multibit, Sigma-Delta modulator

A detailed analysis of the impact of a hysteretic quantizer on a multibit, Sigma-Delta modulator has been carried out in this paper. Both discrete-time and continuous-time modulators have been considered. A qualitative modeling of the hysteretic quantizer based on a hysteretic block followed by an ideal quantizer was proposed. Due to the hysteresis effect, the quantizer output signal is delayed and distorted with respect to the quantizer input signal, where the delay causes a phase-shift independent on the signal frequency. Yet, the effect of the hysteresis depends on the input signal amplitude. This model was validated by using system-level simulations for a second order, 3-bit, discrete-time Sigma-Delta modulator. A linear model for hysteresis was derived by assuming a narrow hysteresis cycle. The quantizer input signal plays a fundamental role in the discussion. In order to include this signal into the linear analysis some approximations are proposed. The quantizer output signal is decomposed by the use of the Fourier series analysis only into the in-phase and quadrature components (with respect to the input signal) whose Fourier series coefficients can be analytically calculated. A quantitative analysis for both a second order, 3-bit, DT and CT Sigma-Delta modulators including a hysteretic quantizer was carried out. For the CT modulator, finite GBW in amplifiers, excess loop delay, and a hysteretic quantizer were considered separately and combined. A good agreement with both system-level simulations and experimental results is found, despite the approximations considered for the quantizer input signal.     

基于双平行马赫曾德尔调制器和受激布里渊散射效应的十倍频毫米波信号生成

提出了一种基于双平行马赫-曾德尔调制器(DPMZ M)和受激布里渊散射(SBS)效应的10倍频mm 波信号生成方案,具有覆盖频段高和频谱纯度高等优点。在本文方案中,低频率的射频(RF )信号通过DPMZM 对激光器发出的光波进行调制,调节直流偏置电压,使DPMZM的主调制器和两个子调制器均 工作在最小传 输点(MITP),抑制光载波和偶数边带,进一步调节两个子调制器的调制深度和移相器的相 移,抑制一阶和 七阶边带,留下三阶和五阶边带,然后利用SBS效应进行布里渊边带滤波滤除三阶边带,仅 保留五阶边带, 再经光电探测器(PD)拍频即可获得10倍频mm波信号。通过仿真实验,以10 GHz的R F信号为驱 动信号,得到了100GHz的mm波信号,验证了方案的可行性。     

New multirate bandpass sigma-delta modulators

A new architecture for fourth- and sixth-order bandpass sigma-delta (BP-SD) modulators is proposed here. The basic BP-SD modulator is obtained from its low-pass (LP) counterpart by means of the standard transformation z/sup -1/ /spl rarr/ -z/sup -2/, which transforms the integrators in the LP modulator into resonators in the BP modulator, and places the input signal band at the frequency f/sub s//4, where f/sub s/ is the sampling rate. In the proposed architecture, the second resonator (and the third one for the sixth-order case) is implemented using a two-path strategy, by means of two high-pass filters (whose poles are located at f/sub s//2) operating in a time-interleaved mode. However, unlike other BP-SD modulators using the two-path strategy, in our approach, the effective sampling frequency in the second resonator (and in the third one for the sixth-order case) is increased to 2/spl middot/f/sub s/ by maintaining the clock rate of the high-pass filters to f/sub s/ which, in turn, places their poles at f/sub s//2. The signal band in the input of the second resonator is moved from the center frequency f/sub s//4 to f/sub s//2 by a modulation process that separates the signal into their in-phase and quadrature components. Another demodulation process in the digital domain reverses this frequency translation of the signal band before the output signal is converted to the analog domain and fed back to the modulator input. A detailed theoretical analysis of the architecture is done in the paper. Owing to the multirate nature of the proposed modulators, simulation results show an improvement of approximately 12 dB in the input dynamic range (fourth-order case) when compared to conventional modulators of the same order clocked at the same frequency rate (in the first resonator).     

基于级联双平行MZM的16倍频光生毫米波技术

为解决毫米波信号生成中存在的困难,提出了一 种基于级联双平行马赫-曾德尔调制器(DPMZM)的16倍频光生毫米波 系统。首先通过控制第1个DPMZM的直流偏压、驱动信号相位差和调制指数,完全抑制光载波 和±2阶边带,获得±4阶光边带;然后将该光波输入到另一个完全一样的DPMZM,获得±8阶光边 带和光载波输出;最后利用光滤波器(OF)滤除光载波,用光电探测器(PD)拍频得到 16倍频的毫米波输出。详细分析 了系统的工作原理,并通过仿真验证了方案的可行性。当输入射频(RF)驱动信号频率为2.5GHz时,可 得到40GHz毫米波输出,并且调制器的调制带宽仅需要 2.5GHz。本文方案具有倍频次数高、频谱纯度好等优点。     

Reconstruction of oversampled band-limited signals fromΣΔ encoded binary sequences

Considers the application of ΣΔ modulators to analog-to-digital conversion. The authors have previously shown that for constant input signals, optimal nonlinear decoding can achieve large gains in signal-to-noise ratio (SNR) over linear decoding. The present paper shows a similar result for band-limited input signals. The new nonlinear decoding algorithm is based on projections onto convex sets (POCS), and alternates between a time-domain operation and a band limitation to find a signal invariant under both. The time-domain operation results in a quadratic programming problem. The band limitation can be based on singular value decomposition of a certain matrix. The authors show simulation results for the SNR performance of a POCS-based decoder and a linear decoder for the single loop, double loop and two-stage ΣΔ modulators and for a specific fourth-order interpolative modulator. Depending on the modulator and the oversampling ratio, improvements in SNR of up to 10-20 dB can be achieved