通信工程文献翻译——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<10和“> 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......

Gain

The 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 amplifier's input impedance will often be much higher than the source impedance, and the load impedance higher than the amplifier's output impedance).

Example: an audio amplifier with a gain given as 20?dB 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). 

Bandwidth

The 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 20?Hz to about 20?kHz (the range of normal human hearing). In ultra high fidelity amplifier design, the amp's frequency response should extend considerably beyond this (one or more octaves either side) and might have ?3 dB points < 10 and > 65?kHz. Professional touring amplifiers often have input and/or output filtering to sharply limit frequency response beyond 20?Hz-20?kHz; too much of the amplifier's 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 ......