Abstract
Essentially, an amplifier is a circuit that for some inputs delivers more power to a load than is received from an input. Amplification is achieved by using a small current or voltage (an input) to control a larger current or voltage provided by a power supply and delivered to a load, as illustrated by Fig. 7.1. For example, in a home audio amplifier, the voltage from a CD player (the source) controls the power delivered to the loudspeaker (the load). Nearly all of the power delivered to the speaker terminals is provided by the amplifier’s power supply, which draws its power from a wall outlet.
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Notes
- 1.
In integrated op amps, transistors with the base connected to the collector often serve as diodes.
- 2.
We treat capacitance in Chapter 8.
- 3.
Real op amps have additional terminals whose functions you will learn when you study electronics.
- 4.
Because of the manner in which the internal circuitry is connected to the supplies, the supplies or supply terminals often are called rails.
- 5.
Also, a small dc offset voltage afflicts virtually all op amps, as described in Section 7.8.
- 6.
Although v pm is small, the individual voltages v p , v n are not necessarily small.
- 7.
Again, the gain of an op amp is so large that if the voltage \({v_p} - {v_n}\) is greater than μ 0/V CC , the amplifier will saturate.
- 8.
Achieving gains less than 10 with an inverting amplifier is attended by several problems, as discussed in Chapter 17.
- 9.
This parameter is not specified on manufacturers’ data sheets and is difficult to measure. The values given here are deduced from other performance data. Related topics are discussed in more detail in Chapter 17.
- 10.
The output stage of an op amp is typically a so called push-pull configuration of two transistors, where one transistor amplifies the positive parts of an applied voltage and the other amplifies the negative parts.
- 11.
This is the power delivered by the supply to the output stage. A typical op amp is a three-stage amplifier, and even if no input is applied (even if \({i_0} = 0\)), some dc power is required to keep the op amp in an active (ready) state.
- 12.
We justify this rule in Chapter 17.
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© 2011 Springer Science+Business Media B.V.
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Glisson, T.H. (2011). Operational Amplifiers I. In: Introduction to Circuit Analysis and Design. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-9443-8_7
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DOI: https://doi.org/10.1007/978-90-481-9443-8_7
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