N_OPAmp_N15 - Operational Amplifiers (Op Amp) (15) Please...

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Operational Amplifiers (Op Amp) (15) 1 Please also refer to: Electronic Devices and Circuit Theory By Robert L. Boylestad
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Operational Amplifiers (Op Amp) 2 Fig. 1 The Basic Op Amp INTRODUCTION An operational amplifier, or op-amp, is a very high gain differential amplifier with high input impedance and low output impedance. Typical uses of the operational amplifier are to provide voltage amplitude changes (amplitude and polarity), oscillators, filter circuits, and many types of instrumentation circuits. An op-amp contains a number of differential amplifier stages to achieve a very high voltage gain. The Figure here, shows a basic op-amp with two inputs and one output as would result using a differential amplifier input stage. Each input results in either the same or an opposite polarity (or phase) output, depending on whether the signal is applied to the plus (+) or the minus (-) input.
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Operational Amplifiers (Op Amp) 3 Figure 2 (a) on left & (b) on right: Single-ended operation Single-Ended Input Single-ended input operation results when the input signal is connected to one input with the other input connected to ground. Figure 2 shows the signals connected for this operation. In Fig. 2a, the input is applied to the plus input (with minus input at ground), which results in an output having the same polarity as the applied input signal. Figure 2b shows an input signal applied to the minus input, the output then being opposite in phase to the applied signal.
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Operational Amplifiers (Op Amp) 4 Figure 3 (a) on left & (b) on right: Double-ended (differential) operation. Double-Ended (Differential) Input In addition to using only one input, it is possible to apply signals at each input—this being a double-ended operation. Figure 3a shows an input, v d , applied between the two input terminals (recall that neither input is at ground), with the resulting amplified output in phase with that applied between the plus and minus inputs. Figure 3b shows the same action resulting when two separate signals are applied to the inputs, the difference signal being v i1 - v i2 .
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Operational Amplifiers (Op Amp) 5 Figure 14.8 Common-mode operation . Common-Mode Operation When the same input signals are applied to both inputs, common-mode operation results, as shown in Fig. 14.8. Ideally, the two inputs are equally amplified, and since they result in opposite polarity signals at the output, these signals cancel, resulting in 0-V output. Practically, a small output signal will result.
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Operational Amplifiers (Op Amp) 6 Figure 14.8 Common-mode operation . Common-Mode Rejection A significant feature of a differential connection is that the signals which are opposite at the inputs are highly amplified, while those which are common to the two inputs are only slightly amplified—the overall operation being to amplify the difference signal while rejecting the common signal at the two inputs. Since noise (any unwanted input signal) is generally common to both inputs, the differential connection tends to provide attenuation of this
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N_OPAmp_N15 - Operational Amplifiers (Op Amp) (15) Please...

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