Chapter 12 Signal generators andwaveform-shaping circuitsIntroduction12.1 Basic principles of sinusoidal oscillators12.2 RC oscillator circuits12.3 LC and crystal oscillators12.4 Bistable Multivibrators12.5 Generation of a standardized pulse-Themonostable multivibratorMicroelectronicCircuits
Microelectronic Circuits Chapter 12 Signal generators and waveform-shaping circuits Introduction 12.1 Basic principles of sinusoidal oscillators 12.2 RC oscillator circuits 12.3 LC and crystal oscillators 12.4 Bistable Multivibrators 12.5 Generation of a standardized pulse-The monostable multivibrator
Introduction(1)linear oscillators:employsapositive-feedbackloopconsistingofanamplifierandanRCorLCfrequency-selectivenetwork.(Section13.1-3)Thetwo(2)nonlinear oscillators or functiondifferentgenerators:approachesThe bistable multivibrator(Section 13.4)theastablemultivibrator (Section13.5)themonostablemultivibrator(Section13.6)MicroelectronicCircuits
Microelectronic Circuits Introduction The two different approaches (1)linear oscillators: employs a positive-feedback loop consisting of an amplifier and an RC or LC frequency-selective network. (Section 13.1-3) (2)nonlinear oscillators or function generators: • The bistable multivibrator(Section 13.4) • the astable multivibrator (Section 13.5) • the monostable multivibrator(Section 13.6)
The basic structure of sinusoidaloscillatorsAmplifier circuit:realize the energy controlFrequency-selectivenetwork:oscillatorThebasicfrequency is determinedstructureX, =XfPositive feedback loop:amplitude control : implementation of thenonlinear amplitude-stabilization mechanismMicroelectronicCircuits
Microelectronic Circuits The basic structure of sinusoidal oscillators The basic structure Amplifier circuit：realize the energy control Frequency-selective network：oscillator frequency is determined Positive feedback loop： amplitude control ：implementation of the nonlinear amplitude-stabilization mechanism i f x = x
Basic Principles of SinusoidalOscillatorThe oscillator feedback loopAmplifierAFrequency-selectivenetworkβThe basic structure of a sinusoidal oscillator.Apositive-feedbackloopisformedbyanamplifier and a frequency-selective networkMicroelectronic Circuits
Microelectronic Circuits Basic Principles of Sinusoidal Oscillator ⚫ The oscillator feedback loop ⚫ The basic structure of a sinusoidal oscillator. ⚫ A positive-feedback loop is formed by an amplifier and a frequency-selective network
Basic Principles of SinusoidalOscillator Feedback signal X,is summed with apositive signThe gain-with-feedback isF:1模电课件\动摄品的产生exeA(s)Af(S)1- A(s)β(s)The oscillation criterion: Barkhausencriterion.L(jo) = A(joo)β(jo) = lPA+P=2nπMicroelectronic Circuits
Microelectronic Circuits Basic Principles of Sinusoidal Oscillator ⚫ Feedback signal xf is summed with a positive sign ⚫ The gain-with-feedback is ⚫ The oscillation criterion: Barkhausen criterion. 1 ( ) ( ) ( ( ) A s s A s A s f − = ） n L j A j j A 2 ( 0 ) ( 0 ) ( 0 ) 1 + = = =
Basic Principles of SinusoidalOscillator Nonlinear amplitude control> To ensure that oscillations will start, the Aβ isslightly greater than unity.> As the power supply is turned on, oscillationwill grown in amplitude.> When the amplitude reaches the desired level.the nonlinear network comes into action andcause the Aβ to exactly unity.Microelectronic Circuits
Microelectronic Circuits Basic Principles of Sinusoidal Oscillator ⚫ Nonlinear amplitude control ➢ To ensure that oscillations will start, the Aβ is slightly greater than unity. ➢ As the power supply is turned on, oscillation will grown in amplitude. ➢ When the amplitude reaches the desired level, the nonlinear network comes into action and cause the Aβ to exactly unity
The implementation of the nonlinearamplitude-stabilization mechanism The first approach makes use of a limitercircuitThe other mechanism for amplitude controlutilizes an element whose resistance canbe controlled by the amplitude of theoutput sinusoid.Microelectronic Circuits
Microelectronic Circuits The implementation of the nonlinear amplitude-stabilization mechanism ⚫ The first approach makes use of a limiter circuit ⚫ The other mechanism for amplitude control utilizes an element whose resistance can be controlled by the amplitude of the output sinusoid
A Popular Limiter Circuit for AmplitudeControl+VWhenviisclosetozero:RDiDi,D,is off v文R,RRiRRR;M0ONORR,+ R+ R?RR4RNBR+ RsR+RD2RVaMicroelectronicCircuits
Microelectronic Circuits A Popular Limiter Circuit for Amplitude Control 4 5 5 4 5 4 2 3 2 2 3 3 1 1 , 2 is off, R R R v R R R v V R R R v R R R v V v R R D D v B o A o I f o + + + = − + + + = = − When vi is close to zero:
A Popular Limiter Circuit for AmplitudeControl+VWhenvigoespositive,D1ison,D2isoffRDi文RRRM1DRRRR2MonthecontraryOvORRMR+VLR.R.NBD2RVaMicroelectronicCircuits
Microelectronic Circuits A Popular Limiter Circuit for Amplitude Control 3 3 2 2 4 4 5 5 1 on the contrary: 1 D D R R L V V R R R R L V V R R − + = − − + = + + When vi goes positive,D1 is on, D2 is off
A Popular Limiter Circuit for AmplitudeControlVOAVOAVR4SlopeSlope=Ri(R,llR.)RiRR,R0Ur0UR,SlopeRRRRVSlopeR?R.RsL(R,lR)SlopeRi(c)(b)>Transfercharacteristicofthelimitercircuit:>When R,is removed, the limiter turns into a comparator with thecharacteristicshownMicroelectronicCircuits
Microelectronic Circuits A Popular Limiter Circuit for Amplitude Control ➢Transfer characteristic of the limiter circuit; ➢When Rf is removed, the limiter turns into a comparator with the characteristic shown. = + + = − − + + − 5 4 5 4 2 3 2 3 1 1 R R V R R L V R R V R R L V D D