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Operational Amplifiers
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The operational amplifier (op-amp).
Note the op-amp has two inputs and one output. Thomas L. Floyd Digital Fundamentals, 8e Copyright ©2003 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Electrical Characteristics
Note these ratings are for specific circuit conditions, and they often include minimum, maximum and typical values. Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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CMRR One rating worth mentioning that is unique to op-amps is CMRR or Common-Mode Rejection Ratio. Because the op-amp has two inputs that are opposite in phase (inverting input and the non-inverting input) any signal that is common to both inputs will be cancelled. A measure of the ability to cancel out common signals is called CMRR. Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Differential and common-mode operation: (a) differential-mode; (b) common-mode.
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VC = ½ ( Vi1 – Vi2 )
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Calculate the CMRR for the circuit measurements shown in Fig.
EXAMPLE Calculate the CMRR for the circuit measurements shown in Fig. (a) (b)
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The value of CMRR is Solution
From the measurement shown in Figure, using the procedure in step 1 above, we obtain The measurement shown in Fig. using the procedure in step 2 above, gives us The value of CMRR is Which can be expressed as
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Ac equivalent of op-amp circuit: (a) practical; (b) ideal.
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Operation of op-amp as constant-gain multiplier: op-amp ac equivalent circuit.
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Operation of op-amp as constant-gain multiplier: ideal op-amp equivalent circuit.
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Operation of op-amp as constant-gain multiplier: redrawn equivalent circuit.
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Virtual ground in an op-amp.
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Inverting constant-gain multiplier.
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Noninverting constant-gain multiplier.
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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A Constant–Gain Amplifier
Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Voltage Buffer Any amplifier with no gain (or loss) is called a unity gain amplifier. The advantages of using a unity gain amplifier: very high input impedance very low output impedance Realistically these circuits will be designed using resistors that are equal (R1 = Rf) to void out problems with offset voltages. Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summing amplifier Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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virtual-ground equivalent circuit.
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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A 4-bit DAC with binary-weighted inputs.
Thomas L. Floyd Digital Fundamentals, 8e Copyright ©2003 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Example : A 4-bit DAC with binary-weighted inputs.
Thomas L. Floyd Digital Fundamentals, 8e Copyright ©2003 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Active Filters Adding capacitors to op-amp circuits provides an external control for the cutoff frequencies. The op-amp active filter provides controllable cutoff frequencies and controllable gain. Low-Pass Filter High-Pass Filter Band pass Filter
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Low-Pass Filter First-order low-pass filter.
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Low-Pass Filter (Cont’d)
Second-order low-pass filter: By adding more RC networks the roll-off can be made steeper.
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High-Pass Filter The lower cutoff frequency:
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Bandpass Filter There are two cutoff frequencies: upper and lower. They can be calculated using the same low-pass cutoff and high-pass cutoff frequency formulas in the appropriate sections.
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Calculate CMRR (dB) for the following Op Amp values:
Questions Calculate CMRR (dB) for the following Op Amp values: Vd = 1 mV, Vo = 200 mV dan Vc = 1 mV, Vo = 30uV.
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Calculate the output voltage if the input voltage is 150mV pmkd
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Calculate the output voltage, Vo
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Calculate the output voltage, Vo
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Calculate the output voltage, Vo
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Determine the cut-off frequency
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Determine the Low and High cut-off frequency
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Calculate the Value of V1 & V2
Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Vo = ? Robert L. Boylestad and Louis Nashelsky Electronic Devices and Circuit Theory, 8e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Vo = ?
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