电子电路基础课件CH.ppt
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1、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 I
2、deal 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 po
3、sitive 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 Operation
4、al 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
5、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
6、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 Ope
7、rational 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
8、 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 impedanc
9、e 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,a
10、n 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 Amplifier
11、s 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
12、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 Oper
13、ational 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 Amplifie
14、rs,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
15、 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 f
16、eedback,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 co
17、nfiguration,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 usuall
18、y 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 volt
19、age 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 Amplif
20、iers 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 superp
21、osition,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 Ope
22、rational 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
23、 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
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