Lectures on FEEDBACK FB-1. Feedback. Analog Circuit Design FB-5 FB-2. Feedback (Cont.) Feedback (Cont.) There are 4 basic kinds of Feedback Circuits :

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Adele Chase
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1 bert W. Brdersen EECS40 University f Clifrni Berkeley Cllege f Engeerg Deprtment f Electricl Engeerg nd Cmputer Science Anlg Circuit Design Lectures n FEEDBACK Feedbck Σ Errr Signl Feedbck Signl fb Bsic Amplifier f Feedbck Amplifier f g f feedbck mplifier FB g f bsic mplifier Feedbck (Cnt.) FB Feedbck (Cnt.) FB5 fb fb f f A ( T Clsed lp g f) f T T Lp G f Open Lp G f Feedbck Fctr A f T» There re 4 bsic kds f Feedbck Circuits : (Type f Feedbck) (Type f Sensg) ) Series (Vltge) Shunt (Vltge) ) Shunt (Current) Shunt (Vltge) 3) Shunt (Current) Series (Current) 4) Series (Vltge) Series (Current)

2 SeriesShunt (ut / ) FB6 SeriesShunt (Cnt.) r FB7 This is vltge mplifier, typicl exmple is the well knwn cnfigurt shwn belw : G r f f SeriesShunt (Cnt.) FB8 SeriesShunt (Cnt.) FB9 G Clcult : ut Clcult (Clsed Lp Output esistnce) : f f T T A Clsed Lp G f f ( f ) ut 0 t i t Drive utput with t, mesure i t t i t r f t 0 ; f t 0 i t f t t r t i r ut t f r T r A 0 f 0. 50, 000 i t t T 0. 50, r 00Ω r 0.0 Ω T

3 Clcult : SeriesShunt (Cnt.) FB0 ShuntShunt (Trnsresistnce ut /i ) r FB i i r ( T ) i r ( T) r i ( T ) r f G G Clcult : ShuntShunt (Cnt.) FB3 ShuntShunt (Cnt.) FB4 f G f G i i hs units f resistnce ( i f G ) i f G T T

4 ShuntShunt (Cnt.) Clcult : FB5 ShuntShunt (Cnt.) ut Clcult (Clsed Lp Output esistnce) : FB6 ε i i f G i f G t i t ( t ) i 0 i f i 0 i t f G ε i r T i t r i t r f G i t r T ShuntSeries (Current Amp i ut /i ) FB7 ShuntSeries (Cnt.) FB8 T i f i i f i i fb i i r i r G Clcult : i i T T f i Clcult : f i i r T ut Clcult (Clsed Lp Output esistnce) : r ( T)

5 SeriesSeries (Trnscnductnce i ut / ) FB9 SeriesSeries (Cnt.) FB0 r G i T G f f fb i G Clcult : r A G i T T f Clcult : f i r ( T ) ut Clcult (Clsed Lp Output esistnce) : r ( T) SeriesShunt Exmple (Withut Ldg) 0 5 r k Ω 9k Ω r 0 kω r r FB A T T SeriesShunt Exmple (Cnt.) FB f T f T 0 k k 9k ( N ldg mens we dn t tken t ccunt the drp crss r due t & ) A precisely 0 t 4 deciml plces f fb fb f 0. r ( T) ( 0 4 ) r 0 4 Ω T 0 4

6 ShuntShunt Exmple (Withut Ldg) FB4 ShuntShunt Exmple (Cnt.) FB5 i r i ( ) i i ShuntShunt Exmple (Cnt.) FB6 ShuntShunt Exmple (Cnt.) FB7 T ( ) r A i T. 0 4 f T kΩ But we wnt O O fb, f f O O i 9 i

7 ShuntShunt Exmple (Cnt.) FB8 ShuntShunt Exmple (Cnt.) FB9 r 0k 0.9Ω T. 0 4 T i ' i ' ' ' ( ') ( ) ( ) ( ') But is nt wht we wnt. ' ( ) ' ShuntShunt Exmple (Cnt.) FB30 SeriesShunt Exmple (With Ldg) Series Shunt with ldg effects f feecbck circuit n the bsic mplifier. FB3 r Bsic mplifier '' ' '' ' '' is the rel put resistnce we wnt, but it desn t cme ut directly sce we used the Nrtn equvlent circuit t the put Fr ldg t OUTPUT ssume pen r IN Fr ldg t INPUT ssume shrt

8 ' SeriesShunt Exmple (Cnt.) r IN r FB3 ' SeriesShunt Exmple (Cnt.) Bsic mp with ldg : ' r r ( ) ( ) r r r ' ε FB33 r IN r ' ε ' IN r ( ' ) r r ' r ( ) r r r ' r ( ) SeriesShunt Exmple (Cnt.) FB34 SeriesShunt Exmple (Cnt.) FB35 fb f ( r ) ( T ') T '» ( r ) r r r T ' ' f r r r T ' < T Becuse f Ldg T ' 0 4 T ' ( 0 5 ) ( 0.) 0k k 9k 0 k 0k withut ldg 0 4 with ldg r T r r ' T ' r T r r r ( ) r r r r

9 ShuntShunt Exmple (With Ldg) FB36 ShuntShunt Exmple (Cnt.) FB37 Trnsfrmg t current surce put : r r OUT i r r OUT ' edrwg : ShuntShunt Exmple (Cnt.) FB38 Bsic mplifier with ldg : ShuntShunt Exmple (Cnt.) FB39 r ' r r ' i r r OUT i r OUT r r ' r Assume shrt fr OUTPUT ldg Assume shrt fr INPUT lsg i r OUT r r r '

10 ShuntShunt Exmple (Cnt.) ' r r r ( r ) r r ' r r OUT ' r FB40 Flly we get : OUT i T ' f G T ' OUT OUT i ShuntShunt Exmple (Cnt.) T ' ' f G r r r FB4 OUT f G OUT OUT T ' T ' ShuntShunt Exmple (Cnt.) FB4 FB43 T '» r ' ' T ' r ' r r r r dependent f OUT OUT '' ' t r OUT ' r r T ' T ' f G ( r ) ' OUT OUT f OUT f Series Shunt OBET W. BODESEN LECTUE 30 FALL,998

11 eplcg current surces with resistnces : i S g mb S χ g m S χ g m i S FB44 OUT Sgle Trnsistr : Series Shunt FB45 g m r OUT S χ g m Open(Series) Shrt(Shunt) i g mb S O S i g mb χ g m f OBET W. BODESEN LECTUE 30 FALL,998 OBET W. BODESEN LECTUE 30 FALL,998 Sgle Trnsistr : Series Shunt (Cnt.) With Ldg : g m OUT r FB46 Sgle Trnsistr : Series Shunt (Cnt.) ' g m r T ' χ g m sce f r» g m A T ' χ g m g m f T ' g m g m ( χ) A ' χ g m FB47 χ g m r OUT ' r S S χ g m χ g m r ' r OUT ' OUT χ g m T ' g m χ g m S g m ( χ) g m ( χ) OBET W. BODESEN LECTUE 30 FALL,998 OBET W. BODESEN LECTUE 30 FALL,998

12 Series Series with Degenert FB48 Series Series Degenert (Cnt.) FB49 L L OUT r Fr Simplicity,χ 0 OPEN (Series) OPEN (Series) S OBET W. BODESEN LECTUE 30 FALL,998 OBET W. BODESEN LECTUE 30 FALL,998 Series Series Degenert (Cnt.) Bsic mplifier with ldg : FB50 Series Series Degenert (Cnt.) Feedbck Netwrk : FB5 L g m r edrwn : g m r r L G r L r OUT ' f T ' G f G g m r r L r ' r OUT ' ( T ') ( r L ) g S m r L r L g m r L ( g m ) r OBET W. BODESEN LECTUE 30 FALL,998 OBET W. BODESEN LECTUE 30 FALL,998

13 Series Series Degenert (Cnt.) FB5 Shunt Shunt FB53 G M T ' f T ' g m r r L g m r g m r S r L g m r r L G F D OUT ' Shrt F Shrt D OUT g G m r g M m L r ( g m ) ( g m ) i ' i G G r» L, OBET W. BODESEN LECTUE 30 FALL,998 OBET W. BODESEN LECTUE 30 FALL,998 Shunt Shunt (Cnt.) FB54 Shunt Shunt (Cnt.) FB55 Bsic mp with ldg : D F F OUT OUT f G F i OUT OUT i G F OUT i G F ( ) g m ( D F r ) ' ( G F ) g m ( D F r ) r ' G F r OUT ' D F T ' f G T '» r ' ' T ' ( G F ) g m ( D F r ) F F G F ( G F ) g m ( D F r ) F g m ( D F r ) F OBET W. BODESEN LECTUE 30 FALL,998 OBET W. BODESEN LECTUE 30 FALL,998

14 Shunt Shunt (Cnt.) FB56 At OUT ' G ' F G G T '» r OUT ' T ' ( D F r ) ( G F ) g m ( D F r ) F g G m F G OBET W. BODESEN LECTUE 30 FALL,998

ANALYSIS OF TRANSISTOR FEEDBACK AMPLIFIERS

ANALYSIS OF TRANSISTOR FEEDBACK AMPLIFIERS ECE 3050 Analysis of s Page 1 ANALYSS F TANSST FEEDBACK AMPLFES Steps n Analyzing s 1. dentify the topology. 2. Determine whether the is positive negative. 3. pen the loop and calculate A, ß,, and o. 4.