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by: Macy Lowe


Macy Lowe
GPA 3.74


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Class Notes
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This 5 page Class Notes was uploaded by Macy Lowe on Monday October 26, 2015. The Class Notes belongs to ECE0257 at University of Pittsburgh taught by Staff in Fall. Since its upload, it has received 49 views. For similar materials see /class/229453/ece0257-university-of-pittsburgh in Electronics and Computer Technology at University of Pittsburgh.

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Date Created: 10/26/15
Course Notes for BB 0257 Introduction to Lasers and Optical Electronics A few words about ampli er circuits Chapter 1 Introduction of Amplifiers 0 Amplifier circuits are the core of any analog circuits 0 Input signal from transducers convert signal in electric form are week 0 Signal amplification is a must before AD conversion filtering noise cancellation encryption FFT modulationdemodulation broadcasting etc etc 0 Now let s discuss in some details on what are those index to characterize performance of a given amplifier Amp circuits This lecture covers Chapter 1416 1 Signal amplification 2 Characteristics used to analyze and gauge amplifier circuits gain linearity saturation nonlinear transfer biasing frequency response 3 Circuit model for amplifiers Characteristics of an Ampcircuit Notes 0 Amplifier circuits symbol 4 This is the only lecture to cover chapter 1 5 You need read section 1113 input Oulpm 6 Section 17 Will not be cover nor required a Circuit symbol for amplifier b An ampli er with a common terminal ground between the input and output ports 1 Voltage gain power gain and current gain o Voltag gain AV E quot I i 0 Current ga1n Ai E quot i P v 139 0 Power ga1n AP E L 0 1 VIII Chapter 1 Introduction to amplifier 1 Course Notes for BB 0257 Introduction to Lasers and Optical Electronics Expressing gain in Decibels 0 Voltage gain in dB 201ogAV dB 0 Current gain in dB 2010gAT dB 0 Voltage gain in dBlOlogAP dB 2 Power supplies An amp needs to draw DCpower to amplify signal signal get more power A more realistic ampcircuit symbol is shown below o In the above figure an amp needs a DC to signal signal so as the need of DC supply This is not convenient in micro electronic circuits sometime that is why many amps need to be biased The Fig b is commonly used as a simplified symbol Pdc VIII V212 Pub 131 13L Pdissipafed 0 Since the power drawn from the signal is usually small the amplifier power efficiency can be defined 77 P L gtlt 100 Pdc 3 Saturation Ideally we hope our amp can remain linear to amplify signal with any strength with the same gain Practically an amp operated from two DC supply can pour out a output voltage more than the voltage of DC supplies So there is a saturation issue illustrated in the follow figure Chapter 1 Introduction to amplifier 39 ll 7quot l H hv a mm L quotv a G3 gt lt g gt 39 5 To avoid distortion of the output signal the input signal must be kept with the linear range L L Sv1 S Nonlinearity and Biasing Practically the transfer function Voutput vs Vinput is not linear at all only part of the transfer function is linear Therefore we need operate the amp at the middle of the linear region shown above this point is referred as DC bias point Q point or operating point or quiescent point This can be done by adding your signal on the top of DC bias voltage Of course both DC bias signal cannot exceed linear range 2 Course Notes for EE 0257 Introduction to Lasers and Optical Electronics vI V Vot Vot Avvit dvo AVd VI Q Example A transistor amplifier has the transfer characteristic v0 10 lO e40VI Find L L dc bias voltage V that results in V0 5 V and gain muquot ID I 0 new mar 11 m 5 Some notations 0 Total instantaneous quantities DC AC signal 139At vct DC quantity IA Vc Power suplly VDD DD Signal quantity pure AC 1395 t vct Amplitude of sine signal In V0 Chapter 1 Introduction to amplifier Frequency response If an amp operates in linear region then an ampcircuit is a linear circuit In we feed a sine signal to a linear circuit the output will be the sine signal with the same frequency however the amplitude and phase Will be different 0 lug I up i lam m r gtl I I I 2 I To characterize the frequency response we need the ratio of output amplitude to the input amplitude and the phase change V a T 0 ltwgt K m 4M w o Bandwidth the band of frequencies over which the gain of the amplifier is ahnost constant to within a certain number of dB usually 3 dB or 50 Anal sis of fre uenc res onse low ass LP and hi h ass HP 7 Couise Notes for BB 0257 Introduction to Lasers and Optical Electronics 0 Lowpass filter Bode plots o Highpass lter Bode plots awlliml In Chapter 1 Introduction to ampli er Circuit models As always any amp circuits must be integrated into a system to perform For any functional electronic circuits it consists tens to thousands unit To analyze the performance and characteristic of the system we must simulate or model individual ampcircuit 1 Voltage amplifier models Course Notes for BB 0257 Introduction to Lasers and Optical Electronics For an ideal amp one needs a few things 0 Large input resistance 0 Respectable voltage gain 0 Low output resistance buffering o Desired power gain These cannot be accomplished by singlestage amp circuit rather we need cascade or multistage ampli er Example evaluate the vltage current and power gain of the following cascade amp J 1 mix 1 r mi til 1kg n ma 1 rota4 Chapter 1 Introduction to ampli er 2 Other ampli er types Although voltageamp is the most popular one in various applications we might wish our amp can amplify different quantity such as robust current ampli cation high output resistance Therefore in different situations we wish to apply different circuit models using either voltage source or current sources TABLE 11 The Four Ampll er Types Circuit Model Gain Parameter Ideal Characteristics 9 quot pevalrcuxl Voltage oim R vi R1 A RF Type Vollagc Amplifier tinmm Ampli er Transconducmnce mpli cl Slinl i ircml Transmnducwnc R m Gm E 1 AN R39 39r n Trunsresismme fl R v Am i 1 gt quotr OpenCil uullTmnsreslsiimte R lt 0 i i Rm 5 L VIA R n i


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