【正文】 ble, offering selective output within their specified frequency range. Musical instrument (audio) amplifiers Main articles: Instrument amplifier and Audio amplifier An audio amplifier is usually used to amplify signals such as music or speech Background: 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 中北大學 2021 屆畢業(yè)設(shè)計說明書 第 8 頁 共 15 頁 requires high fT (at least 310 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 gainbandwidth 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 bee 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 3dB losses at theirs inputs and outputs. Technology: University researchers have developed a design method by bining threestage 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 13 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 work, therefore, a 3dB loss is avoidable. S11 can be kept low over the operating bandwidth even with DC supply varied from 0 to , 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 fiberoptic munications as a modulator driver, limiting, automatic gain control and as transimpedance amplifiers. It can also be employed in various bands of frequencies as generalpurpose amplifiers in 中北大學 2021 屆畢業(yè)設(shè)計說明書 第 9 頁 共 15 頁 wireless munication 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. 中北大學 2021 屆畢業(yè)設(shè)計說明書 第 10 頁 共 15 頁 低功耗高增益寬帶放大器 中文翻譯 增益 放大器的增益是輸出或輸入功率之比，通常以分貝衡量。s potential output power would otherwise be wasted 中北大學 2021 屆畢業(yè)設(shè)計說明書 第 2 頁 共 15 頁 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. Efficiency Efficiency is a measure of how much of the power source is usefully applied to the amplifier39。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 mon and wellaccepted metric is the half power points (. 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 (otherw