低功耗高增益宽带放大器外文翻译.doc

中北大学2010届毕业设计说明书a broadband amplifier with huge gain-bandwidth product and low power consumption gainthe gain of an amplifier is the ratio of output to input power or amplitude, and is usually measured in decibels. (when measured in decibels it is logarithmically related to the power ratio: g(db)=10 log(pout /(pin). rf amplifiers are often specified in terms of the maximum power gain obtainable, while the voltage gain of audio amplifiers and instrumentation amplifiers will be more often specified (since the amplifiers input impedance will often be much higher than the source impedance, and the load impedance higher than the amplifiers output impedance).example: an audio amplifier with a gain given as 20db will have a voltage gain of ten (but a power gain of 100 would only occur in the unlikely event the input and output impedances were identical). bandwidththe bandwidth of an amplifier is the range of frequencies for which the amplifier gives satisfactory performance. the definition of satisfactory performance may be different for different applications. however, a common and well-accepted metric is the half power points (i.e. frequency where the power goes down by half its peak value) on the output vs. frequency curve. therefore bandwidth can be defined as the difference between the lower and upper half power points. this is therefore also known as the 3 db bandwidth. bandwidths (otherwise called frequency responses) for other response tolerances are sometimes quoted (1 db, 6 db etc.) or plus or minus 1db (roughly the sound level difference people usually can detect).the gain of a good quality full-range audio amplifier will be essentially flat between 20hz to about 20khz (the range of normal human hearing). in ultra high fidelity amplifier design, the amps frequency response should extend considerably beyond this (one or more octaves either side) and might have 3 db points 65khz. professional touring amplifiers often have input and/or output filtering to sharply limit frequency response beyond 20hz-20khz; too much of the amplifiers potential output power would otherwise be wasted on infrasonic and ultrasonic frequencies, and the danger of am radio interference would increase. modern switching amplifiers need steep low pass filtering at the output to get rid of high frequency switching noise and harmonics.efficiencyefficiency is a measure of how much of the power source is usefully applied to the amplifiers output. class a amplifiers are very inefficient, in the range of 1020% with a max efficiency of 25% for direct coupling of the output. inductive coupling of the output can raise their efficiency to a maximum of 50%.class b amplifiers have a very high efficiency but are impractical for audio work because of high levels of distortion (see: crossover distortion). in practical design, the result of a tradeoff is the class ab design. modern class ab amplifiers are commonly between 3555% efficient with a theoretical maximum of 78.5%.commercially available class d switching amplifiers have reported efficiencies as high as 90%. amplifiers of class c-f are usually known to be very high efficiency amplifiers.more efficient amplifiers run cooler, and often do not need any cooling fans even in multi-kilowatt designs. the reason for this is that the loss of efficiency produces heat as a by-product of the energy lost during the conversion of power. in more efficient amplifiers there is less loss of energy so in turn less heat.in rf power amplifiers, such as cellular base stations and broadcast transmitters, specialist design techniques are used to improve efficiency. doherty designs, which use a second transistor, can lift efficiency from the typical 15% up to 30-35% in a narrow bandwidth. envelope tracking designs are able to achieve efficiencies of up to 60%, by modulating the supply voltage to the amplifier in line with the envelope of the signal.linearityan ideal amplifier would be a totally linear device, but real amplifiers are only linear within limits.when the signal drive to the amplifier is increased, the output also increases until a point is reached where some part of the amplifier becomes saturated and cannot produce any more output; this is called clipping, and results in distortion.in most amplifiers a reduction in gain takes place before hard clipping occurs; the result is a compression effect, which (if the amplifier is an audio amplifier) sounds much less unpleasant to the ear. for these amplifiers, the 1 db compression point is defined as the input power (or output power) where the gain is 1 db less than the small signal gain. sometimes this nonlinearity is deliberately designed in to reduce the audible unpleasantness of hard clipping under overload.the problem of nonlinearity is most often solved with negative feedback.linearization is an emergent field, and there are many techniques, such as feedforward, predistortion, postdistortion, eer, linc, callum, cartesian feedback, etc., in order to avoid the undesired effects of the non-linearities.noisethis is a measure of how much noise is introduced in the amplification process. noise is an undesirable but inevitable product of the electronic devices and components, also much noise results from intentional economies of manufacture and design time. the metric for noise performance of a circuit is noise figure or noise factor. noise figure is a comparison between the output signal to noise ratio and the thermal noise of the input signal.output dynamic rangeoutput dynamic range is the range, usually given in db, between the smallest and largest useful output levels. the lowest useful level is limited by output noise, while the largest is limited most often by distortion. the ratio of these two is quoted as the amplifier dynamic range. more precisely, if s = maximal allowed signal power and n = noise power, the dynamic range dr is dr = (s + n ) /n.1in many switched mode amplifiers, dynamic range is limited by the minimum output step size.slew rateslew rate is the maximum rate of change of the output, usually quoted in volts per second (or microsecond). many amplifiers are ultimately slew rate limited (typically by the impedance of a drive current having to overcome capacitive effects at some point in the circuit), which sometimes limits the full power bandwidth to frequencies well below the amplifiers small-signal frequency response.rise timethe rise time, tr, of an amplifier is the time taken for the output to change from 10% to 90% of its final level when driven by a step input. for a gaussian response system (or a simple rc roll off), the rise time is approximated by:tr * bw = 0.35, where tr is rise time in seconds and bw is bandwidth in hz.settling time and ringingthe time taken for the output to settle to within a certain percentage of the final value (for instance 0.1%) is called the settling time, and is usually specified for oscilloscope vertical amplifiers and high accuracy measurement systems. ringing refers to an output variation that cycles above and below an amplifiers final value and leads to a delay in reaching a stable output. ringing is the result of overshoot caused by an underdamped circuit.overshootin response to a step input, the overshoot is the amount the output exceeds its final, steady-state value.stabilitystability is an issue in all amplifiers with feedback, whether that feedback is added intentionally or results unintentionally. it is especially an issue when applied over multiple amplifying stages.stability is a major concern in rf and microwave amplifiers. the degree of an amplifiers stability can be quantified by a so-called stability factor. there are several different stability factors, such as the stern stability factor and the linvil stability factor, which specify a condition that must be met for the absolute stability of an amplifier in terms of its two-port parameters.electronic amplifiersmain article: electronic amplifierthere are many types of electronic amplifiers, commonly used in radio and television transmitters and receivers, high-fidelity (hi-fi) stereo equipment, microcomputers and other electronic digital equipment, and guitar and other instrument amplifiers. critical components include active devices, such as vacuum tubes or transistors. a brief introduction to the many types of electronic amplifier follows.power amplifierthe term power amplifier is a relative term with respect to the amount of power delivered to the load and/or sourced by the supply circuit. in general a power amplifier is designated as the last amplifier in a transmission chain (the output stage) and is the amplifier stage that typically requires most attention to power efficiency. efficiency considerations lead to various classes of power amplifier: see power amplifier classes.vacuum tube (valve) amplifiersmain article: valve amplifierthe glow from four electro harmonix kt88 brand power tubes lights up the inside of a traynor yba-200 guitar amplifieraccording to symons, while semiconductor amplifiers have largely displaced valve amplifiers for low power applications, valve amplifiers are much more cost effective in high power applications such as radar, countermeasures equipment, or communications equipment (p.56). many microwave amplifiers are specially designed valves, such as the klystron, gyrotron, traveling wave tube, and crossed-field amplifier, and these microwave valves provide much greater single-device power output at microwave frequencies than solid-state devices (p.59).2valves/tube amplifiers also have niche uses in other areas, such asin russian military aircraft, for their emp tolerance niche audio for their sound qualities transistor amplifiersmain articles: transistor, bipolar junction transistor, audio amplifier, and mosfetthe essential role of this active element is to magnify an input signal to yield a significantly larger output signal. the amount of magnification (the forward gain) is determined by the external circuit design as well as the active device.many common active devices in transistor amplifiers are bipolar junction transistors (bjts) and metal oxide semiconductor field-effect transistors (mosfets).applications are numerous, some common examples are audio amplifiers in a home stereo or pa system, rf high power generation for semiconductor equipment, to rf and microwave applications such as radio transmitters.transistor-based amplifier can be realized using various configurations: for example with a bipolar junction transistor we can realize common base, common collector or common emitter amplifier; using a mosfet we can realize common gate, common source or common drain amplifier. each configuration has different characteristic (gain, impedance.).operational amplifiers (op-amps)main articles: operational amplifier and instrumentation amplifieran operational amplifier is an amplifier circuit with very high open loop gain and differential inputs which employs external feedback for control of its transfer function or gain. although the term is today commonly applied to integrated circuits, the original operational amplifier design was implemented with valves.fully differential amplifiers (fda)main article: fully differential amplifiera fully differential amplifier is a solid state integrated circuit amplifier which employs external feedback for control of its transfer function or gain. it is similar to the operational amplifier but it also has differential output pins.video amplifiersthese deal with video signals and have varying bandwidths depending on whether the video signal is for sdtv, edtv, hdtv 720p or 1080i/p etc. the specification of the bandwidth itself depends on what kind of filter is used and which point (-1 db or -3 db for example) the bandwidth is measured. certain requirements for step response and overshoot are necessary in order for acceptable tv images to be presented.oscilloscope vertical amplifiersthese are used to deal with video signals to drive an oscilloscope display tube and can have bandwidths of about 500mhz. the specifications on step response, rise time, overshoot and aberrations can make the design of these amplifiers extremely difficult. one of the pioneers in high bandwidth vertical amplifiers was the tektronix company.distributed amplifiersmain article: distributed amplifierthese use transmission lines to temporally split the signal and amplify each portion separately in order to achieve higher bandwidth than can be obtained from a single amplifying device. the outputs of each stage are combined in the output transmission line. this type of amplifier was commonly used on oscilloscopes as the final vertical amplifier. the transmission lines were often housed inside the display tube glass envelope.switched mode amplifiersthese nonlinear amplifiers have much higher efficiencies than linear amps, and are used where the power saving justifies the extra complexity.negative resistance devicesnegative resistances can be used as amplifiers, such as the tunnel diode amplifier.microwave amplifierstravelling wave tube (twt) amplifiersmain article: traveling wave tubeused for high power amplification at low microwave frequencies. they typically can amplify across a broad spectrum of frequencies; however, they are usually not as tunable as klystrons.klystronsmain article: klystronvery similar to twt amplifiers, but more powerful and with a specific frequency sweet spot. they generally are also much heavier than twt amplifiers, and are therefore ill-suited for light-weight mobile applications. klystrons are tunable, offering selective output within their specified frequency range.musical instrument (audio) amplifiersmain articles: instrument amplifier and audio amplifieran audio amplifier is usually used to amplify signals such as music or speechbackground: without a distributed amplifier, most broadband amplifier bandwidths can be achieved around 1/10 to 1/3 of their ft only. therefore, a high bandwidth amplifier requires high ft (at least 3-10 times of the amplifier bandwidth) transistors in order to achieve high bandwidth. unfortunately, the current device technology is limited and in very high ft transistors, yield is still low. this leads to high cost and low yield.even if high gain-bandwidth product could be achieved by a distributed amplifier, the major disadvantages of the distributed amplifier are large area, and high dc power consumption. transistors were operated with high current density for high ft in order to achieve high bandwidth amplification. however, the transistors would become highly stressed resulting in reliability problems and short lifetimes. 50 ohm terminations are currently employed at the input and output of broadband amplifiers in order to obtain desirable input and output broadband impedance matches (low s11 and s22). however, the disadvantage is 3-db losses at theirs inputs and outputs. technology: university researchers have developed a design method by combining three-stage amplifier design to achieve a broadband amplifier with desirable gain, large bandwidth, low power consumption, low input/output reflection coefficients, low loss, and good reliability. without a distributed amplifier, the invented broadband amplifier bandwidth of 1/2 of ft and/or approaching to ft can be achieved. therefore, the amplifiers requires only ft of 1-3 times of the amplifier bandwidth in order to achieve high bandwidth. the broadband amplifier area and dc power consumption will be small and low respectively. with the invented broadband amplifier, transistors are operated with typical current density, but high amplifier bandwidth can still be achieved. therefore, the transistors are not stressed at high current density, thus leading to better reliability and long lifecycles. also, 50 termination is not required in the input and output broadband matching network, therefore, a 3-db loss is avoidable. s11 can be kept low over the operating bandwidth even with dc supply varied from 0 to 3.3v, and s22 is low over the operating bandwidth as well. this advantage is very useful for broadband amplifiers, and they can be easily cascaded as well. application: the invented broadband amplifier can be applied in fiber-optic communications as a modulator driver, limiting, automatic gain control and as transimpedance amplifiers. it can also be employed in various bands of frequencies as general-purpose amplifiers in wireless communication systems, in testing equipments, and in military electronics warfare systems.the quality of an amplifier can be characterized by a number of specifications, listed below. 低功耗高增益宽带放大器 中文翻译增益放大器的增益是输出或输入功率之比，通常以分贝衡量。（当它是对数分贝测量相关的功率比：g(db)=10 log(pout /(pin)）。射频放大器往往在最大功率增益所取，而音频放大器的电压增益和仪表放大器将更加经常指定（因为放大器的输入阻抗，往往会比源阻抗较高，负载阻抗高于放大器的输出阻抗）。例如：20分贝将有10倍的电压增益（100倍功率增益，只会发生在的输入和输出阻抗是一样的情况）带宽放大器的带宽是表示放大器提供了“良好”的频率范围，可为不同的应用。然而，共同的和普遍接受的衡量标准是半功率点（即在断电的频率降低一半的峰值）在输出与频率的曲线。因此，带宽可以被定义为下限和上限之间的半功率点的差异。因此，这是也是众所周知的-3 db带宽。带宽（或称为“频率响应”公差为其他反应），有时引用（-1分贝，-6分贝等），或“加或减为1db”（大致音量差异的人通常可以检测到）。 一个良好的质量赢得全音域音频放大器将基本持平，20赫兹至20千赫（正常人类的听觉范围）。超高保真放大器设计，放大器的频率响应应该大大超过这个扩展（一个或多个八度任何一方），并有可能-3 db点 65千赫。专业旅游放大器往往输入和/或输出滤波大力限制频率超过20赫兹，20赫兹的反应;太多的放大器的潜在输出功率很大，否则是对声波和超声波频率浪费，以及调幅无线电干扰的危险会增加。现代开关放大器必须在陡峭的低通滤波的输出获得的高开关频率的噪声和谐波消除。效率 效率是如何的权力来源是非常有用的应用到放大器的输出措施。 a类放大器是非常低效的10-20之间，与25的输出直接耦合最大效率。电感耦合的输出可以提高效率50为上限。 b类放大器具有很高的效率，而且是因为高层次的失真（见：交叉失真音频工作不切实际）。在实际设计中，一个折衷的结果是ab类设计。 ab类放大器是现代之间通常35-55，其中78.5的理论最大效率。 市售d类开关放大器有报道高达90的效率。 cf卡类放大器通常被称为是非常高效率的放大器。 更高效的放大器运行冷却器，而且往往并不需要，即使在多千瓦的冷却风扇的设计。此是，由于生产效率损失按损失的能源产品的过程中能量转换热能的原因。在更有效的放