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| university:courses:electronics:text:chapter-9 [06 Jun 2017 17:22] – [9.4.5 Voltage Follower (common collector or drain) Lab Activities] Doug Mercer | university:courses:electronics:text:chapter-9 [02 May 2019 23:35] – [9.5.2 Small signal input impedance with emitter/source degeneration] Sergiy Gavrylenko |
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| Again looking at the small signal models in figure 9.3.1 we see that for both the BJT case and the MOS case the output impedance is the parallel combination of R<sub>L</sub> and r<sub>o</sub>. We can generally assume this is true if we consider that V<sub>in</sub> is driven from a low impedance (nearly ideal) voltage source. If this is not the case then the finite output impedance must be added in series with r<sub>o</sub>. If the input of the current follower is driven by the relatively high output impedance of a transconductance amplifier such as the common emitter or source amplifier from earlier then the output impedance for the combined amplifier can be very high. For most practical applications we can ignore r<sub>o</sub> because it is very often much larger than R<sub>L</sub>. | Again looking at the small signal models in figure 9.3.1 we see that for both the BJT case and the MOS case the output impedance is the parallel combination of R<sub>L</sub> and r<sub>o</sub>. We can generally assume this is true if we consider that V<sub>in</sub> is driven from a low impedance (nearly ideal) voltage source. If this is not the case then the finite output impedance must be added in series with r<sub>o</sub>. If the input of the current follower is driven by the relatively high output impedance of a transconductance amplifier such as the common emitter or source amplifier from earlier then the output impedance for the combined amplifier can be very high. For most practical applications we can ignore r<sub>o</sub> because it is very often much larger than R<sub>L</sub>. |
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| | **ADALM1000 Lab Activity, [[university:courses:alm1k:alm-lab-cb|BJT Common Base Amplifier]]**\\ |
| | **ADALM1000 Lab Activity, [[university:courses:alm1k:alm-lab-cg|BJT Common Gate Amplifier]]**\\ |
| | **ADALM1000 Lab Activity, [[university:courses:alm1k:alm-lab-fca|Folded Cascode Amplifier]]** |
| ==== 9.4 Voltage followers (also called Emitter or Source follower or Common collector or drain amplifiers) ==== | ==== 9.4 Voltage followers (also called Emitter or Source follower or Common collector or drain amplifiers) ==== |
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| **ADALM2000 Lab Activity 11, [[university:courses:electronics:electronics-lab-11|BJT Emitter follower]]**\\ | **ADALM2000 Lab Activity 11, [[university:courses:electronics:electronics-lab-11|BJT Emitter follower]]**\\ |
| **ADALM2000 Lab Activity 11m, [[university:courses:electronics:electronics-lab-11m|MOS Source follower]] | **ADALM2000 Lab Activity 11m, [[university:courses:electronics:electronics-lab-11m|MOS Source follower]]** |
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| =====9.5 Series Feedback: emitter/source degeneration===== | =====9.5 Series Feedback: emitter/source degeneration===== |
| Again looking at the small signal models in figure 9.4.1 we see that for the BJT case the input V<sub>in</sub> see r<sub></sub>in series with degeneration resistor R<sub>E</sub> as a load. For the MOS case V<sub>in</sub> see basically an open circuit. | Again looking at the small signal models in figure 9.4.1 we see that for the BJT case the input V<sub>in</sub> see r<sub></sub>in series with degeneration resistor R<sub>E</sub> as a load. For the MOS case V<sub>in</sub> see basically an open circuit. |
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| {{ :university:courses:electronics:text:chptr9-e21.png?200 |}} | {{ :university:courses:electronics:text:chptr9-e19.png?200 |}} |
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| ====9.5.3 Small signal output impedance with emitter/source degeneration==== | ====9.5.3 Small signal output impedance with emitter/source degeneration==== |
