Ch7 Operational Amplifiers and Op Amp Circuits

7.1 Operational Amplifiers 7.2 Op Amp Circuits7.3 Active Filter7.4 Op Amp Positive FeedbackCircuits and Analog ElectronicsReferences: Floyd-Ch6; Gao-Ch7, 9;

7.1 Operational Amplifiers Key Words: Op Amp Model Ideal Op Amp Op Amp transfer characteristic Feedback Virtual shortCh7 Operational Amplifiers and Op Amp Circuits

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers (Op Amp )Inverting input At a minimum, op amps have 3 terminals: 2 input and 1 output. An op amp also requires dc power to operate. Often, the op amp requires both positive and negative voltage supplies (V+ and V-).

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Symbol One of the input terminals (1) is called an inverting input terminal denoted by - The other input terminal (2) is called a non-inverting input terminal denoted by +

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers The Op Amp Model The op amp is designed to sense the difference between the voltage signals applied to the two input terminals and then multiply it by a gain factor A such that the voltage at the output terminal is A(v+-v-). The voltage gain A is very large (practically infinite). The gain A is often referred to as the differential gain or open-loop gain. The input resistance Rin is very large (practically infinite). The output resistance Ro is very small (practically zero).

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Ideal Op Amp

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers For A741, A = 100dB=105 if vo=10V

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Op Amp transfer characteristic curve

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Op Amp transfer characteristic curveSo far, we have been looking at the amplification that can be achieved for relatively small (amplitude) signals. For a fixed gain, as we increase the input signal amplitude, there is a limit to how large the output signal can be. The output saturates as it approaches the positive andnegative power supply voltages. In other words, there is limited range across which the gain is linear.

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers ReviewIdeal op amp characteristics: Does not draw input current so that the input impedance is infinite (i.e., i1=0 and i2=0) The output terminal can supply an arbitrary amount of current (ideal VCVS) and the output impedance is zero The op amp only responds to the voltage difference between the signals at the two input terminals and ignores any voltages common to both inputs. In other words, an ideal op amp has infinite common-mode rejection. A is or can be treated as being infinite.

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers What happens when A is very large?

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Suppose A=106, R1=9R, R2=R, Closed-loop gain: determined by resistor ratio insensitive to A, temperature

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback Why did this happen?

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback Observe, under negative feedback,analysis method under negative feedback! Hence, we say there is a virtual short between the two terminals (+ and -) .

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback When R1=0, R2=, Buffer: voltage gain = 1Voltage Follower

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback We can adjust the closed-loop gain by changing the ratio of R2 and R1. The closed-loop gain is (ideally) independent of op amp open-loop gain A (if A is large enough) and we can make it arbitrarily large or small and with the desired accuracy depending on the accuracy of the resistors.

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback The terminal 1 is a virtual ground since terminal 2 is grounded.Inverting configuration,This is a classic example of what negative feedback does. It takes an amplifier with very large gain and through negative feedback, obtain a gain that is smaller, stable, and predictable. In effect, we have traded gain for accuracy. This kind of trade off is common in electronic circuit design as we will see more later.

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback Inverting configuration,Input Resistance:Assuming an ideal op amp (open-loop gain A = infinity), in the closed-loop inverting configuration, the input resistance is R1.

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback Inverting configuration,Output Resistance:Roa is usually small and so Rout is negligible when A is large

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Negative feedback Inverting configuration,

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Homework1) Design a circuit to 2) Find the vo=?

Ch7 Operational Amplifiers and Op Amp Circuits7.1 Operational Amplifiers Review: Two fundamental Op Amp

Structure AfInput voltage ( )terminalFeed back ( )terminalInverting Amp__Non inverting Amp+_

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsKey Words: Subtracting Amplifiers Summing Amplifiers Intergrator Differentiator

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsInverting Configuration with General Impedances

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsConsider this circuit:Subtraction!

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsAnother way of solving use superpositionSubtracting Amplifiers

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsAnother way of solving use superpositionSubtracting Amplifiers

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsAnother way of solving use superpositionSubtracting Amplifiers

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsSubtracting AmplifiersAnother way of solving use superposition

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsSubtracting Amplifiersvo1

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsSumming Amplifiers

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsWeighted SummerWe can also build a summer:

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsExample 1 Design a summer which has an output voltage given by vO=1.5vs1-5vs2+0.1vs3

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsExample 1 Design an summer which has an output voltage given by vO=1.5vs1-5vs2+0.1vs3Solution 2:

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsLets build an integratorLets start with the following insight:But we need to somehow convert voltage vI to current.

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsFirst try use resistorWhen is vO small compared to vR?for good integratorRC >> 1

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsTheres a better way

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsTheres a better way

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsIntegratorHow about in the frequency domain?

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsIntegrator

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsIntegrator

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsIntegratorWhile the DC gain in the previous integrator circuit is infinite, the amplifier itself will saturate.To limit the low-frequency gain to a known and reliable value, add a parallel resistor to thecapacitor.What does the magnitude response look like?

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsNow, lets build a differentiatorLets start with the following insights:But we need to somehow convert current to voltage.

Ch7 Operational Amplifiers and Op Amp Circuits7.2 Op Amp CircuitsDifferentiator

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active FilterKey Words: Basic Filter Responses Low-Pass Filter High-Pass Filter Band-Pass Filter Band-Stop Filter

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter Basic Filter Responses

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter Low-Pass Filter

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter High-Pass Filter

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active FilterAdvantages of Filter

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter Low-Pass Filter

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter Low-Pass FilterFirst-order (one-pole) Filter

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter Low-Pass FilterSecond-order (two-pole) Filter

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter Low-Pass FilterVoltage-controlled voltage source(VCVS) filter A

7.3 Active Filter Low-Pass FilterVoltage-controlled voltage source(VCVS) filter ACh7 Operational Amplifiers and Op Amp Circuits

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter High-Pass Filter Circuit: RC

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter Band-Pass Filter

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Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active Filter Band-Stop Filter

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Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active FilterExample 2 For the circuit shown, show that what it is filter?The Inverting First-order Low-Pass Filter.

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active FilterExample 2 For the circuit shown, show that what it is filter?The Inverting First-order High-Pass Filter.

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active FilterExample 2 For the circuit shown, show that what it is filter?The Non-Inverting Band-Stop Filter(Second-order).

Ch7 Operational Amplifiers and Op Amp Circuits7.3 Active FilterExample 2 For the circuit shown, show that what it is filter?The Inverting Band-Pass Filter. (Second-order)The Inverting High-Pass Filter. (Second-order)

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackKey Words: Positive Feedback The Comparator Oscillator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackPositive Feedback

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackPositive Feedback

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe ComparatorThe op amp is often used as a comparator.The output voltage exhibits two stable states. The output state depends on the relative value of one input voltage compared to the other input voltage. Threshold voltages

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator

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Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe ComparatorTransmission characteristics

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator with Positive FeedbackPositive feedback is often used with comparator circuits. The feedback is applied from the output to the non-inverting input of the op amp.

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator with Positive Feedback

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator (Schmidt trigger)

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator (Schmidt trigger)When vi

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator (Schmidt trigger)

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator (Schmidt trigger)Without hysteresis

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator (Schmidt trigger)Oscillator can create a clock

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Comparator (Schmidt trigger)Theres a better way----triangular-wave generator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Wien-Bridge Oscillator (RC Oscillator )Positive FeedbackLead-lag networkOp Amp Circuits

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Wien-Bridge Oscillator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Wien-Bridge Oscillator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Wien-Bridge Oscillator-

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Wien-Bridge Oscillator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Wien-Bridge Oscillator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe Wien-Bridge OscillatorAll practical methods to achieve stability for feedback oscillators require the gain to be self-adjusting. This requirement is a form of automatic gain control.Negative temperaturecoefficient

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe LC Oscillator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe LC OscillatorResistors CircuitInductance CircuitCapacitance Circuit

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe RC(Phase-Shift) Oscillator

Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe LC Oscillator

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Ch7 Operational Amplifiers and Op Amp Circuits7.4 Op Amp Positive FeedbackThe LC Oscillator

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