As stated before, an ideal differential amplifier only amplifies the voltage difference between its two inputs. If the two inputs of a differential amplifier were to be shorted together (thus ensuring zero potential difference between them), there should be no change in output voltage for any amount of voltage applied between those two shorted inputs [...]
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OPERATIONAL AMPLIFIERS : part 15 (Drift and Frequency response)
Being semiconductor devices, op-amps are subject to slight changes in behavior with changes in operating temperature. Any changes in op-amp performance with temperature fall under the category of op-amp drift. Drift parameters can be specified for bias currents, offset voltage, and the like. Consult the manufacturer’s data sheet for specifics on any particular op-amp. To [...]
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OPERATIONAL AMPLIFIERS : part 13 (Offset voltage)
Another practical concern for op-amp performance is voltage offset. That is, effect of having the output voltage something other than zero volts when the two input terminals are shorted together. Remember that operational amplifiers are differential amplifiers above all: they’re supposed to amplify the difference in voltage between the two input connections and nothing more. [...]
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OPERATIONAL AMPLIFIERS : part 4 (Divided feedback)
If we add a voltage divider to the negative feedback wiring so that only a fraction of the output voltage is fed back to the inverting input instead of the full amount, the output voltage will be a multiple of the input voltage (please bear in mind that the power supply connections to the op-amp [...]
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OPERATIONAL AMPLIFIERS : part 8 (Building a differential amplifier)
An op-amp with no feedback is already a differential amplifier, amplifying the voltage difference between the two inputs. However, its gain cannot be controlled, and it is generally too high to be of any practical use. So far, our application of negative feedback to op-amps has resulting in the practical loss of one of the [...]
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OPERATIONAL AMPLIFIERS : part 11 (Positive feedback)
As we’ve seen, negative feedback is an incredibly useful principle when applied to operational amplifiers. It is what allows us to create all these practical circuits, being able to precisely set gains, rates, and other significant parameters with just a few changes of resistor values. Negative feedback makes all these circuits stable and self-correcting. The [...]
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Transistor:Input and output coupling
To overcome the challenge of creating necessary DC bias voltage for an amplifier’s input signal without resorting to the insertion of a battery in series with the AC signal source, we used a voltage divider connected across the DC power source. To make this work in conjunction with an AC input signal, we “coupled” the [...]
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The common-base amplifier
The final transistor amplifier configuration (Figure below) we need to study is the common-base. This configuration is more complex than the other two, and is less common due to its strange operating characteristics. Common-base amplifier It is called the common-base configuration because (DC power source aside), the signal source and the load share the base [...]
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The common-collector amplifier
Our next transistor configuration to study is a bit simpler for gain calculations. Called the common-collector configuration, its schematic diagram is shown in Figure below. Common collector amplifier has collector common to both input and output. It is called the common-collector configuration because (ignoring the power supply battery) both the signal source and the load [...]
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OPERATIONAL AMPLIFIERS : part 17 (Operational amplifier models)
While mention of operational amplifiers typically provokes visions of semiconductor devices built as integrated circuits on a miniature silicon chip, the first op-amps were actually vacuum tube circuits. The first commercial, general purpose operational amplifier was manufactured by the George A. Philbrick Researches, Incorporated, in 1952. Designated the K2-W, it was built around two twin-triode [...]
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OPERATIONAL AMPLIFIERS : part 14 (Bias current)
Inputs on an op-amp have extremely high input impedances. That is, the input currents entering or exiting an op-amp’s two input signal connections are extremely small. For most purposes of op-amp circuit analysis, we treat them as though they don’t exist at all. We analyze the circuit as though there was absolutely zero current entering [...]
