Electronic Devices and Circuit Theory 10th Edition Boylestad Louis Chapter 11 Op AMP Applications
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Chapter 11 Op-Amp Applications
OpOp-Amp Applications Constant-gain multiplier ConstantVoltage summing Voltage buffer Controlled sources Instrumentation circuits Active filters
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Constant--Gain Amplifier Constant Inverting Version
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Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Constant--Gain Amplifier Constant Noninverting Version
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Multiple--Stage Gains Multiple The total gain (3-stages) is given by:
A = A1 A 2 A 3 or
R f R f R f − A = 1 + − R 1 R2 R3
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Voltage Summing
The output is the sum of individual signals times the gain: R R R Vo = − f V1 + f V2 + f V3 R2 R3 R1
[Formula 14.3] Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Voltage Buffer Any amplifier with no gain or loss is called a unity gain amplifier. amplifier The advantages of using a unity gain amplifier: • Very high input impedance • Very low output impedance Realistically these circuits are designed using equal resistors (R1 = Rf) to avoid problems with offset voltages.
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Controlled Sources Voltage-controlled voltage source VoltageVoltage--controlled current source Voltage Current--controlled voltage source Current Current--controlled current source Current
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Voltage--Controlled Voltage Source Voltage The output voltage is the gain times the input voltage. What makes an op-amp different from other amplifiers is its impedance characteristics and gain calculations that depend solely on external resistors.
Noninverting Amplifier Version
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Voltage--Controlled Voltage Source Voltage The output voltage is the gain times the input voltage. What makes an op-amp different from other amplifiers is its impedance characteristics and gain calculations that depend solely on external resistors.
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
Inverting Amplifier Version
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Voltage--Controlled Current Source Voltage
The output current is:
Io =
V1 = kV1 R1
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Current--Controlled Voltage Source Current This is simply another way of applying the op-amp operation. Whether the input is a current determined by Vin/R1 or as I1 : Vout =
− Rf Vin R1
or
Vout = −I 1 R L
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Current--Controlled Current Source Current This circuit may appear more complicated than the others but it is really the same thing. R Vout = − f Vin R in Vout Vin =− Rf R 1 || R 2 Vout V = − in Rf R in
Io = −
Vin R 1 || R 2
R + R2 I o = − Vin 1 R R × 1 2 V R + R2 I o = − in 1 R 1 R 2 R I o = − I 1 + 1 = kI R2
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Instrumentation Circuits Some examples of instrumentation circuits using opamps: • Display driver • Instrumentation amplifier
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Display Driver
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Instrumentation Amplifier
For all Rs at the same value (except Rp): 2R (V1 − V2 ) = k (V1 − V2 ) Vo = 1 + RP
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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Active Filters Adding capacitors to op-amp circuits provides external control of the cutoff frequencies. The op-amp active filter provides controllable cutoff frequencies and controllable gain. • Low-pass filter • High-pass filter • Bandpass filter
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Low--Pass Filter— Low Filter—First First--Order
The upper cutoff frequency and voltage gain are given by:
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
f OH =
18
1 2 πR 1 C 1
Av = 1+
Rf R1
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Low--Pass Filter— Low Filter—Second Second--Order
The roll-off can be made steeper by adding more RC networks.
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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High--Pass Filter High
The cutoff frequency is determined by:
f OL =
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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1 2 πR 1 C 1
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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 highpass cutoff frequency formulas in the appropriate sections.
Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky
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