【正文】 gy 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 3035% 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. Linearity An 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 bees saturated and cannot produce any more output。 too much of 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 (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 fullrange 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 amp39。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 input impedance will often be much higher than the source impedance, and the load impedance higher than 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。s potential output power would otherwise be wasted 中北大學(xué) 2021 屆畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 第 2 頁(yè) 共 15 頁(yè) 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。 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 clipping occurs。s smallsignal frequency response. Rise time The 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 = , where tr is rise time in seconds and BW is bandwidth in Hz. Settling time and ringing The time taken for the output to settle to within a certain percentage of the final value (for instance %) 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 amplifier39。s stability can be quantified by a socalled 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 t