tailieunhanh - Ebook Electronic devices and circuit theory (7th edition): Part 2
(BQ) Part 2 book "Electronic devices and circuit theory" has contents: BJT and JFET frequency response, linear digital ICs, sinusoidal alternating waveforms, operational amplifiers, Op-Amp applications, power amplifiers, power supplies, oscilloscope and other measuring instruments,.and other contents. | f CHAPTER BJT and JFET Frequency Response 11 INTRODUCTION The analysis thus far has been limited to a particular frequency. For the amplifier, it was a frequency that normally permitted ignoring the effects of the capacitive elements, reducing the analysis to one that included only resistive elements and sources of the independent and controlled variety. We will now investigate the frequency effects introduced by the larger capacitive elements of the network at low frequencies and the smaller capacitive elements of the active device at the high frequencies. Since the analysis will extend through a wide frequency range, the logarithmic scale will be defined and used throughout the analysis. In addition, since industry typically uses a decibel scale on its frequency plots, the concept of the decibel is introduced in some detail. The similarities between the frequency response analyses of both BJTs and FETs permit a coverage of each in the same chapter. LOGARITHMS There is no escaping the need to become comfortable with the logarithmic function. The plotting of a variable between wide limits, comparing levels without unwieldy numbers, and identifying levels of particular importance in the design, review, and analysis procedures are all positive features of using the logarithmic function. As a first step in clarifying the relationship between the variables of a logarithmic function, consider the following mathematical equations: a ϭ bx, x ϭ logb a () The variables a, b, and x are the same in each equation. If a is determined by taking the base b to the x power, the same x will result if the log of a is taken to the base b. For instance, if b ϭ 10 and x ϭ 2, a ϭ bx ϭ (10)2 ϭ 100 but x ϭ logb a ϭ log10 100 ϭ 2 In other words, if you were asked to find the power of a number that would result in a particular level such as shown below: 10,000 ϭ 10x 493 f the level of x could be determined using logarithms. That is, x ϭ log10 10,000 ϭ 4 For the .
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