如何为便携式音频应用选用耳机放大器

目前市场上许多耳机放大器的设计遵循classAB、class D及class G等拓扑结构,并被放置在DAC和CODEC等输出端IC.选用放大器的首要原则包括成本因素,以及所涉及设备的物理尺寸,相连的外接器件、音频性能、所需电源电压,以及功耗和效率等.对于以电池作为动力驱动的手持设备(例如便携式媒体播放器和移动通信终端等)来说,在设计与耳机相连的放大器及其输出端IC时,系统设计师则必须仔细权衡这些选用原则中的每一条来作为工作的指导.     

模拟开关在手持和便携式设备中应用

手持式和便携式电子产品的市场正在不断增长，原因之一在于它们能提供附加的功能性，如新性能及节省空间的特点。模拟开关正是这些电子产品实现新功能和减小印刷线路板面积的关键元件。在移动电话和其它手持式电子产品中，模拟开关一般被用来将音频信号引导至耳机、在共通功能之间选择通用信号，以及在RC网络之间进行多路转换。模拟开关还可免除笔记本电     

为便携式娱乐设备配置的新型高品质耳机放大器

当今消费者对于高端娱乐的需求不断增长，犹如在使用便携式设备(如笔记本电脑等)时能享受着聆听音乐、影视剧和新闻的崭新方式。同时。还要求灵活性更强、品质更佳的多功能产品，以获得在移动或固定使用状态下获得最佳聆听体验。     

为便携式系统增加先进外设

现在,诸如Wi-Fi和微型硬盘技术在嵌入式领域已被迅速采用,这些应用包括基于VoIP（基于IP协议的语音）手机、智能电话和PDA、媒体播放器和导航助手等便携式产品。要集成这些先进外设而又不缩短电池的寿命是一个严峻的挑战,而这正是新型反熔丝的FPGA（现场可编程门阵列）所关注的焦点,这种FPGA可以为一个优化的架构提供有效的智能桥接。     

顺应便携式医疗保健应用的需求

两种趋势影响着医疗和工业设备设计人员:一是便携性,二是此类设备越来越多地用于消费和实验室应用。血糖监控仪、多参数血液分析仪、脉搏血氧仪、PH计和环境监控仪就是其中的例子,这些设备一度仅存在于     

零漂移高带宽的电流检测放大器

AD8218是一款精密电流检测放大器，在恹成本封装内，提供独特的高带宽与极低漂移组合特性。其采用专有CMOS工艺制造，在-40～＋125℃的温度范围内，其零漂移内核仅有＋100nV／℃的失调漂移，同时能够保持500kIIz的典型小信号带宽。     

D级放大器IC促进便携式的应用

D级音频功率放大器能把音频信号输出到扬声器,与传统的AB级音频功率放大器相比,其效率要高2～3倍。效率的增加使得这些放大器很适合在便携式应用中使用。     

用于便携式产品的低成本音频方案

音频放大器是便携式产品(PDA、手机、笔记本电脑、PVR等)中必不可少的处理电路，随着这些产品日益多功能化和小型化，传统的多片解决方案已不能满足小尺寸的需求，此外，生产厂商也日益注重产品的音频品质以迎合消费者的需求。     

高速蓝牙为便携式装置带来的新应用

里程碑 蓝牙（Bluetooth）市场近年以惊人的速度成长，每周出货量约1000万件，每天约有3种产品通过认证。2005年底，超过5亿个产品已配备Bluetooth解决方案。     

LCD在无线／便携式设备中的应用

LCD的应用范围正随着其自身技术的不断进步变得日益广泛。电信、互联网设备、测试/测量仪器、手持式数据管理设备、控制板自动显示器、办公设备、笔记本电脑和电子游戏机等诸多门类的产品都是LCD一展身手的舞台。在无线/便携式设备领域(比如蜂窝电话和PDA),LCD仍然显现出比其他显示器技术更胜一筹的设计优势。     

Asymmetrically Modulated AC Chopper

The paper describes a current impulse-commutated ac triac chopper employed to obtain the optimum supply power factor correction for reactive loads. The resultant displacement and distortion factors of the supply and efficiency of the load are considered. Theoretical results are in excellent agreement with results obtained experimentally.     

升降压斩波电路和Cuk斩波电路的Simulink仿真对比

现代电力电子技术的基础是电力电子器件,它可以用来实现主电路中电能的变换或控制.绝缘栅双极晶闸管（IGBT）拥有GTR和MOSFET两种器件的优点,因此具有优良的特性,在中、大功率电力电子设备中应用广泛.该文借用Simulink对buck-boost变换电路和Cuk斩波电路进行了仿真,并分析两种功能一样的斩波电路在性能上的差异.     

A CMOS Chopper Offset-Stabilized Opamp

In this paper, an offset-stabilized operational amplifier is described. The amplifier employs a chopper amplifier in a low frequency path to cancel the offset of a wide-bandwidth amplifier. A sample-and-hold circuit is used to reduce the chopper ripple, and the low frequency path is also offset-stabilized to further reduce the residual offset. The amplifier has less than 1.5 offset at a 16-kHz chopper frequency, a unity gain frequency of 1.3 MHz with a 50-pF load, and draws 700 from a 5-V supply. The amplifier was realized in a 0.7 CMOS process, and has an effective chip area of 3.6.     

基于锁相环的高稳定性斩光器的设计

描述了一种采用锁相环来稳定斩光频率的设计方法.将斩光盘组件代替锁相环中的压控振荡器,就可以构成锁相电机控制系统,并由此得到数学模型.通过对其传输函数的分析,可以依次作出环路的奈奎斯特图、根轨迹图和波特图.通过奈奎斯特图能够了解环路的稳定条件;通过根轨迹图能进一步看到当改变环路参数时环路闭环极点在复平面上的移动情况;波特图则显示出环路的稳定余量.合理选择环路参数能保证环路的可靠锁定及良好的动态性能.经测试,应用本方案,斩光器的斩光频率能达到晶体级的稳定性(优于100×10-6/℃),相位抖动小于1%,能极好地满足相关检测技术的要求.     

Bandwidth enhancement of a microstrip-line-fed printed wide-slotantenna

Printed wide-slot antennas fed by a microstrip line with a fork-like tuning stub for bandwidth enhancement are proposed and experimentally investigated. Both the impedance and radiation characteristics of this antenna are studied. Experimental results indicate that a 1:1.5 VSWR bandwidth of 1 GHz is achieved at operating frequencies around 2 GHz, which is nearly ten times that of a conventional microstrip-line-fed printed wide-slot antenna. It also achieved a 2-dB gain bandwidth of at least 0.5 GHz     

Bandwidth improvement of a homojunction p-i-n photodiode

This paper presents an analytical study of the impact of doping profile in the p and n regions on the improvement of the bandwidth of a homo-junction p-i-n photodiode. In this study, nonuniformly doped p and n regions are considered. Thus, due to the nonuniformity in the doping, an electric field is established in both the p and n regions. Thereby, if the field is in the right direction, it will aid the diffusion of electrons and holes from p and n regions into the i region. Through these results, it is found that the bandwidth of the nonuniform photodiode is improved from 7 GHz, for uniformly doped p and n regions, to over 30 GHz. Whereas in this proposed structure, the bandwidth is comparable to that obtained for a double heterostructure photodiode, with the advantage of higher quantum efficiency     

Optimal Bandwidth Allocation in a Delay Channel

In this paper, we consider the problem of allocating bandwidth to two queues with arbitrary arrival processes, so as to minimize the total expected packet holding cost over a finite or infinite horizon. Bandwidth is in the form of time slots in a time-division multiple-access schedule. Allocation decisions are made based on one-step delayed queue backlog information. In addition, the allocation is done in batches, in that a queue can be assigned any number of slots not exceeding the total number in a batch. We show for a two queue system that if the holding cost as a function of the packet backlog in the system is nondecreasing, supermodular, and superconvex, then: 1) the value function at each slot will also satisfy these properties; 2) the optimal policy for assigning a single slot is of the threshold type; and 3) optimally allocating$M$slots at a time can be achieved by repeatedly using a policy that assigns each slot optimally given the previous allocations. Thus, the problem of finding the optimal allocation strategy for a batch of slots reduces to that of optimally allocating a single slot, which is conceptually much easier to obtain. These results are applied to the case of linear and equal holding costs, and we also present a special case where the above results extend to more than two queues.     

铁电型非制冷红外焦平面探测器的调制器设计

从铁电型非制冷红外焦平面探测器逐行读出的工作机理和阿基米德螺旋线的定义出发,导出了多调制周期调制器叶片形状的设计公式,给出了调制器与探测器位置关系的设计实例,解决了调制器设计的核心问题.     

热释电斩波器控制

斩波器是热释电型热像仪的重要组成部份,其平稳、匀速且按要求相位精确地运转,关系到整机成像质量的好坏。提出了一种对热释电斩波器进行闭环控制的方法,该方法的使用,解决了斩波器的控制问题。     

Analysis and Performance of a Chopper Controlled Separately Excited DC Motor

A combination of Fourier analysis of load voltage waveform and Laplace transformation is applied for determining the performance of a separately excited dc motor fed from a chopper controlled supply, under all modes of operation. The analysis takes into account the commutation interval and the results show that contrary to the assumption made in works reported earlier, commutation interval significantly affects the performance. For the case of continuous conduction, independent expressions for current and speed are obtained in terms of applied voltage, load torque, and chopper and machine parameters. However, in the case of discontinuous conduction, Fourier coefficients include speed voltage as an additional quantity and hence the equations for current and speed have to be solved as simultaneous equations. The analysis is used to predict the steady-state and transient response. Computed torque-speed characteristics are compared with the results obtained experimentally.