Lect_10 - ECE442 SolidStateDevices&Circuits...

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ECE 342–Jose Schutt Aine 1 ECE 442 Solid State Devices & Circuits 10. Frequency Response of Amplifiers Jose E. Schutt-Aine Electrical & Computer Engineering University of Illinois jschutt@emlab.uiuc.edu
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ECE 342–Jose Schutt Aine 2 Low-Pass Circuit In frequency domain: 1 1 i o V V j C R jC ω =⋅ + 1 11 io ov i VV VA j RC V j RC ωω =⇒ = = ++ 2 / v A jR C j f f ==
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ECE 342–Jose Schutt Aine 3 2 11 22 f RC π πτ == 2t i m e c o n s t a n t RC τ = = Low-Pass Circuit
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ECE 342–Jose Schutt Aine 4 High-Pass Circuit 11 1 ii o VR V V R jC jR C ωω == ++ 2 1 1/ 1 2 o v i V A Vj f f j fRC π = 2 1 2 f RC =
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ECE 342–Jose Schutt Aine 5 If f 2 = 2f 1 , then f 2 is one octave above f 1 If f 2 = 10f 1 , then f 2 is one decade above f 1 22 21 0 11 # log 3.32log ff of octaves == 2 10 1 #l o g f of decades f = 2 GHz is one octave above 1 GHz 10 GHz is one decade above 1 GHz Octave & Decade
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ECE 342–Jose Schutt Aine 6 3dB points are points at which the magnitude is 1/ 2 20log(1.414) 3 dB Ad B == 1 2 oo VV j = + that at midband frequencies. 3 dB Definition From which Power is halved. Voltage is scaled as:
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ECE 342–Jose Schutt Aine 7 Amplifier has intrinsic gain A o 1 1/ hi jf f + Low-pass characteristics is: High-pass characteristics is: Overall gain A(f) is: / lo lo jf f jf f + / 1 () lo o lo hi jf f Af A jf f jf f =⋅ ++ Gain
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ECE 342–Jose Schutt Aine 8 At very high frequencies, STC goes as 2 20log 1(/ ) o G ωω =− + 20log( / ) 20 log( / ) oo GX w h e r e X ω −= = ± Slope of curve is –20; so if X=1 ( =10 o ), decrease is –20 dB Î -20 dB/decade Gain
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ECE 342–Jose Schutt Aine 9 Three Frequency Bands
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ECE 342–Jose Schutt Aine 10 Model for general Amplifying Element C c1 and C c2 are coupling capacitors (large) Î μ F C in and C out are parasitic capacitors (small) Î pF
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ECE 342–Jose Schutt Aine 11 Midband Frequencies - Coupling capacitors are short circuits - Parasitic capacitors are open circuits out in L MB in g in out L vR R AA R R R == ++
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ECE 342–Jose Schutt Aine 12 Low Frequency Model - Coupling capacitors are present - Parasitic capacitors are open circuits 1 1 1 1 1() in in in c in ab cg i n gi n c vR v j CR v j CR R RR jC ω == ++ 1 1 () i n in ab in n i n R R R vv R R + =⋅ +
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ECE 342–Jose Schutt Aine 13 Low Frequency Model () 12 2 1 11 2 2 ll L out c gi n c define f and f R RC RR C π == + + 1 1 / 1/ in l ab in n l Rj f f vv j f f =⋅ ++ 2 2 / , l L out ab L out l jf f R Similarly v Av j f f
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ECE 342–Jose Schutt Aine 14 12 // 1/ out in l l L in g in L out l l vR j f f j f f R Overall gain A R R R j f f j f f == ++ + + out l l MB in l l vj f f j f f A f f j f f =⋅ Low Frequency Model
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ECE 342–Jose Schutt Aine 15 R out = 3 k Ω , R g =200 Ω , R in =12 k Ω , R L =10 k Ω C c1 =5 μ F and C c2 =1 μ F 1 6 1 2.61 2 (12,200 5 10 ) l fH z π == ×× Example 2 6 1 12.2 2 (13,000 10 ) l f Hz ×
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ECE 342–Jose Schutt Aine 16 High Frequency Model - Assume coupling capacitors are short - Account for parasitic capacitors 1 th g in R RR = & 1 in in th gi n vR V = + Potential Thevenin equivalent for input as seen by C in
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ECE 342–Jose Schutt Aine 17 1 1 1 in in ab gi n i n t h vR v R R j CR ω =⋅ ++ 1 11 1/ 2 in in
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This note was uploaded on 01/24/2012 for the course ECE 342 taught by Professor Nareshshanbhag during the Spring '11 term at University of Illinois, Urbana Champaign.

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Lect_10 - ECE442 SolidStateDevices&Circuits...

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