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| university:courses:electronics:text:chapter-3 [31 Aug 2013 16:27] – [3: Introduction and Chapter Objectives] Doug Mercer | university:courses:electronics:text:chapter-3 [06 Jun 2017 16:49] (current) – [3.2.3 Loop gain] Doug Mercer | ||
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| ====3.2.1 Noise Gain (NG) ==== | ====3.2.1 Noise Gain (NG) ==== | ||
| - | The first aid to analyzing op amps circuits is to differentiate between noise gain and signal gain. We have already discussed the differences between non-inverting and inverting stages as to their signal gains, which are summarized in equations 3.1 and 3.2, respectively. But, as can be noticed from figure 3.1, the difference between an inverting and non-inverting stage can be as simple as just where the reference ground is placed. For a ground at point G1, the stage is an inverter; conversely, if the ground is placed at point G2 (with no G1) the stage is non-inverting. | + | The first aid to analyzing op amps circuits is to differentiate between noise gain and signal gain. We have already discussed the differences between non-inverting and inverting stages as to their signal gains, which are summarized in equations 3.1 and 3.2, respectively. But, as can be noticed from figure 3.1, the difference between an inverting and non-inverting stage can be as simple as just where the reference ground is placed. |
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| This loop gain discussion emphasizes that indeed, loop gain is a very significant factor in predicting the performance of closed-loop operational amplifier circuits. The open-loop gain required to obtain an adequate amount of loop gain will, of course, depend on the desired closed-loop gain. | This loop gain discussion emphasizes that indeed, loop gain is a very significant factor in predicting the performance of closed-loop operational amplifier circuits. The open-loop gain required to obtain an adequate amount of loop gain will, of course, depend on the desired closed-loop gain. | ||
| - | For example, using equation 3-9, an amplifier with A< | + | For example, using equation 3-9, an amplifier with A< |
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| + | **ADALM1000 Lab Activity [[university: | ||
| ====3.2.4 Frequency Dependence of Loop Gain ==== | ====3.2.4 Frequency Dependence of Loop Gain ==== | ||
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| Figure 3.2 illustrates that the high open-loop gain figures typically quoted for op amps can be somewhat misleading. As noted, beyond a few Hz, the open-loop gain falls at 6dB/octave. Consequently, | Figure 3.2 illustrates that the high open-loop gain figures typically quoted for op amps can be somewhat misleading. As noted, beyond a few Hz, the open-loop gain falls at 6dB/octave. Consequently, | ||
| - | A direct approach to improving loop gain at high frequencies other than by increasing open-loop gain is to increase the amplifier open-loop bandwidth. figure 3.2 shows this in terms of two simple examples. It should be borne in mind however that op amp gain-bandwidths available today extend to the hundreds of MHz, allowing video and high-speed communications circuits to fully exploit the virtues of feedback. | + | A direct approach to improving loop gain at high frequencies other than by increasing open-loop gain is to increase the amplifier open-loop bandwidth. figure 3.2 shows this in terms of two simple examples. It should be borne in mind however that op amp gain-bandwidths available today extend to the hundreds of MHz, allowing video and high-speed communications circuits to fully exploit the virtues of feedback. |
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| + | **ADALM1000 Lab Activity [[university: | ||
| ====3.2.5 The Bode Plot: Asymptotic And Actual Responses==== | ====3.2.5 The Bode Plot: Asymptotic And Actual Responses==== | ||
university/courses/electronics/text/chapter-3.txt · Last modified: 06 Jun 2017 16:49 by Doug Mercer