【正文】 erms of its twoport parameters. Electronic amplifiers Main article: Electronic amplifier There are many types of electronic amplifiers, monly used in radio and television transmitters and receivers, highfidelity (hifi) stereo equipment, microputers and other electronic digital equipment, and guitar and other instrument amplifiers. Critical ponents 中北大學(xué) 2021 屆畢業(yè)設(shè)計說明書 第 5 頁 共 15 頁 include active devices, such as vacuum tubes or transistors. A brief introduction to the many types of electronic amplifier follows. Power amplifier The 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) amplifiers Main article: Valve amplifier The glow from four Electro Harmonix KT88 brand power tubes lights up the inside of a Traynor YBA200 guitar amplifier According 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 munications equipment (p. 56). Many microwave amplifiers are specially designed valves, such as the klystron, gyrotron, traveling wave tube, and crossedfield amplifier, and these microwave valves provide much greater singledevice power output at microwave frequencies than solidstate devices (p. 59).[2] Valves/tube amplifiers also have niche uses in other areas, such as in russian military aircraft, for their EMP tolerance niche audio for their sound qualities Transistor amplifiers Main articles: Transistor, Bipolar junction transistor, Audio amplifier, and MOSFET The 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 mon active devices in transistor amplifiers are bipolar junction transistors (BJTs) and metal oxide semiconductor fieldeffect transistors (MOSFETs). 中北大學(xué) 2021 屆畢業(yè)設(shè)計說明書 第 6 頁 共 15 頁 Applications are numerous, some mon 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. Transistorbased amplifier can be realized using various configurations: for example with a bipolar junction transistor we can realize mon base, mon collector or mon emitter amplifier。 however, they are usually not as tunable as klystrons. Klystrons Main article: Klystron Very 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 illsuited for lightweight mobile applications. Klystrons are tunable, 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(xué) 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 resear