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【正文】 are necessary in order for acceptable TV images to be presented. Oscilloscope vertical amplifiers These are used to deal with video signals to drive an oscilloscope display tube and can have bandwidths of about 500 MHz. 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 pany. 中北大學(xué) 2021 屆畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 第 7 頁(yè) 共 15 頁(yè) Distributed amplifiers Main article: Distributed Amplifier These 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 bined in the output transmission line. This type of amplifier was monly used on oscilloscopes as the final vertical amplifier. The transmission lines were often housed inside the display tube glass envelope. Switched mode amplifiers These nonlinear amplifiers have much higher efficiencies than linear amps, and are used where the power saving justifies the extra plexity. Negative resistance devices Negative resistances can be used as amplifiers, such as the tunnel diode amplifier. Microwave amplifiers Travelling wave tube (TWT) amplifiers Main article: Traveling wave tube Used for high power amplification at low microwave frequencies. They typically can amplify across a broad spectrum of frequencies。 the result is a pression effect, which (if the amplifier is an audio amplifier) sounds much less unpleasant to the ear. For these amplifiers, the 1 dB pression point is defined as the input power (or output power) where the gain is 1 dB less than the small signal gain. Someti mes 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 nonlinearities. Noise This 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 ponents, 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 parison between the output signal to noise ratio and the thermal noise of the input signal. Output dynamic range Output 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.[1] In many switched mode amplifiers, dynamic range is limited by the minimum output step size. Slew rate Slew 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 overe capacitive effects at some point in the circuit), which sometimes limits the full power bandwidth to frequencies well below the 中北大學(xué) 2021 屆畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 第 4 頁(yè) 共 15 頁(yè) amplifier39。 too much of the amplifier39。中北大學(xué) 2021 屆畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 第 1 頁(yè) 共 15 頁(yè) A Broadband Amplifier with Huge Gainbandwidth Product and Low Power Consumption 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 amplifier39。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 Hz20 kHz。 this is called clipping, and results in distortion. 中北大學(xué) 2021 屆畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 第 3 頁(yè) 共 15 頁(yè) In most amplifiers a reduction in gain takes place before hard
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