电子电路基础课件CH.ppt
Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers 7.2 Op Amp Circuits7.3 Active Filter7.4 Op Amp Positive Feedback,Circuits and Analog Electronics,Readings:Gao-Ch7,Ch9;Floyd-Ch6,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,Key Words:Op Amp Model Ideal Op Amp Op Amp transfer characteristic Feedback Virtual short,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 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 Circuits,7.1 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 Circuits,7.1 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 some 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 Circuits,7.1 Operational Amplifiers,Ideal Op Amp,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,For A741,A=100dB=105，if vo=10V，,Then,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,Op Amp transfer characteristic curve,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,Op Amp transfer characteristic curve,So 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 Circuits,7.1 Operational Amplifiers,Review,Ideal 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 Circuits,7.1 Operational Amplifiers,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,What happens when“A”is very large?,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 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 Circuits,7.1 Operational Amplifiers,Negative feedback,Why did this happen?,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,Negative feedback,Observe,under negative feedback,analysis method under negative feedback!,So,we say there is a virtual short between the two terminals(“+”and“-”).,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,Negative feedback,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,Negative feedback,When R1=0,R2=,Buffer:voltage gain=1,Voltage Follower,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,Negative feedback,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 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 of desired accuracy depending on the accuracy of the resistors.,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 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 of later.,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 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 Circuits,7.1 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 Circuits,7.1 Operational Amplifiers,Negative feedback,Inverting configuration,We can model the closed-loop inverting amplifier(with A=infinite)with the following equivalent circuit using a voltage-controlled voltage source,Ch7 Operational Amplifiers and Op Amp Circuits,7.1 Operational Amplifiers,Homework,1)Design a circuit to,2)Find the vo=?,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Key Words:Subtracting Amplifiers Summing Amplifiers Intergrator Differentiator,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Inverting Configuration with General Impedances,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Let,Consider this circuit:,Subtraction!,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Another way of solving use superposition,Subtracting Amplifiers,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Another way of solving use superposition,Subtracting Amplifiers,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Another way of solving use superposition,Subtracting Amplifiers,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Subtracting Amplifiers,Another way of solving use superposition,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Subtracting Amplifiers,Let,Let,vo1,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Summing Amplifiers,For node N，,Let,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Weighted Summer,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Example 1,Design an summer which has an output voltage given by vO=1.5vs1-5vs2+0.1vs3。,we have，,Let,。,Let，,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Example 1,Design an summer which has an output voltage given by vO=1.5vs1-5vs2+0.1vs3。,Solution 2:,Let,Because,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Lets build an intergrator,Lets start with the following insight:,But we need to somehow convert voltage vI to current.,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,First try use resistor,When is vO small compared to vR?,for good integratorRC 1,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Theres a better way,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Theres a better way,But,vO must be very small compared to vR,or else,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Intergrator,How about in the frequency domain?,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Intergrator,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Intergrator,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Intergrator,While 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 Circuits,7.2 Op Amp Circuits,Now,lets build a differentiator,Lets start with the following insights:,But we need to somehow convert current to voltage.,Ch7 Operational Amplifiers and Op Amp Circuits,7.2 Op Amp Circuits,Differentiator,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Key Words:Basic Filter Responses Low-Pass Filter High-Pass Filter Band-Pass Filter Band-Stop Filter,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Basic Filter Responses,voltage gain,Filter,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Low-Pass Filter,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,High-Pass Filter,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Advantages of Filter,where,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Low-Pass Filter,-20dB/decade,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Low-Pass Filter,First-order(one-pole)Filter,Second-order(two-pole)Filter,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Low-Pass Filter,Voltage-controlled voltage source(VCVS)filiter,A,For simplicity,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,High-Pass Filter,Transfer functions:,Circuit:RC,Frequency domain,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Band-Pass Filter,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Band-Stop Filter,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Exp.2,For the circuit shown,show that what it is filter?,(a),The Inverting First-order Low-Pass Filter.,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Exp.2,For the circuit shown,show that what it is filter?,(b),The Inverting First-order High-Pass Filter.,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Exp.2,For the circuit shown,show that what it is filter?,(c),The Non-Inverting Band-Stop Filter(Second-order).,Ch7 Operational Amplifiers and Op Amp Circuits,7.3 Active Filter,Exp.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 Circuits,7.4 Op Amp Positive Feedback,Key Words:Positive Feedback The Comparator Oscillator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,Positive Feedback,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,Positive Feedback,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator,The 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 Circuits,7.4 Op Amp Positive Feedback,The Comparator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator with Positive Feedback,Positive 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 Circuits,7.4 Op Amp Positive Feedback,The Comparator with Positive Feedback,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator(Schmidt trigger),Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator(Schmidt trigger),When vi（0，,When viVTH1，vOVO-0，,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator(Schmidt trigger),Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator(Schmidt trigger),Without hysteresis,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator(Schmidt trigger),Oscillator can create a clock,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Comparator(Schmidt trigger),Theres a better way-triangular-wave generator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Wien-Bridge Oscillator(RC Oscillator),Positive FeedbackLead-lag network,Op Amp Circuits,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Wien-Bridge Oscillator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Wien-Bridge Oscillator,-,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Wien-Bridge Oscillator,-,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Wien-Bridge Oscillator,The phase shift through the network is 0 for,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Wien-Bridge Oscillator,Loop gain of 1 causes a sustained constant output,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The Wien-Bridge Oscillator,All 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 Circuits,7.4 Op Amp Positive Feedback,The LC Oscillator,Admittance,-Quality Factor,Impedance,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The LC Oscillator,Resistors Circuit,Inductance Circuit,Capacitance Circuit,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The RC(Phase-Shift)Oscillator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The LC Oscillator,Ch7 Operational Amplifiers and Op Amp Circuits,7.4 Op Amp Positive Feedback,The LC Oscillator,
