FYSE400 ANALOG ELECTRONICS

Transcription

1 YS400 NLOG LCONCS LCU 12 eedback plfer 1 uptn 1. he bac aplfer unlateral. 2. he gan OL f the bac aplfer deterned wthut feedback. 3. he calculated gan OL laded gan : ladng f the feedback netwrk, urce and lad retane are ntced. 4. he feedback netwrk unlateral. 2

2 Outlne f naly 1. dentfy the tplgy X f current r vltage. 2. Draw the bac aplfer crcut wthut feedback eplace each actve devce by t prper del. dentfy X f and X n the crcut btaned. 3. valuate : β X f X valuate OL by applyng KL and KCL t the equvalent crcut btaned. 4. r OL and β, fnd and 5. r the equvalent crcut fnd D and OD. pply the Backan pedance frula t btan and O. 3 plgy f a yte nput rt tep dentfy nput lp t cntan, and (a) bae-t-etter regn f the bplar trantr. (b) gate-t-urce regn f the frt n the aplfer (c) the ectn between the tw nput f a dfferental r peratnal aplfer. plgy f nput lp Sere tplgy ( ltage urce ) n the nput crcut, there a crcut cpnent W n ere wth. nd W cnnected t the utput (prtn f the yte cntanng the lad). ltage acr W feedback gnal X f f 4

3 plgy f a yte nput rt tep dentfy nput lp plgy f nput lp Shunt tplgy ( Current urce ) Defne nput nde (a) he bae f the frt BJ (b) he gate f the frt (c) he nvertng ternal f a dfferental r peratnal aplfer. Shunt tplgy f there a cnnectn between the nput nde and the utput crcut. he current n th cnnectn the feedback gnal X f f 5 plgy f a yte Output Secnd tep Defne Output Nde he vltage (wth repect t grund) at the utput nde appear acr the lad retr ( L ) and utput current the current n L. plgy f utput lp Shunt tplgy Set ( L 0) (hrt-crcutng the utput) X f 0 ( ltage aplng ) plgy f utput lp Sere tplgy Set ( L ) (pen-crcutng the utput) X f 0 ( Current aplng ) 6

4 plfer wthut feedback hrd tep OL and β Calculate the gan f the bac aplfer wthut feedback but takng the ladng f the β netwrk nt accunt. Mdfy crcut frt nput crcut : Output tplgy hunt Output tplgy ere ltage aplng Current aplng Shrt-crcut utput nde Open-crcut the utput lp Output crcut : nput tplgy hunt nput tplgy ere Current cparn ltage cparn Shrt-crcut nput nde 0 Open-crcut the nput lp 0 (nne f the feedback current enter t the aplfer nput) (nne f the feedback vltage reache the aplfer nput) 7 plgy f the tter fllwer nput : Seral tplgy ltage cparn nput lp nput lp cntan, whch cnnected t the utput. f Output : Shunt tplgy ltage aplng By ettng, the feedback elnated and f. hu the utput hunt cnnected. Sere-Shunt tplgy 8

5 plfer wthut feedback Mdfed nput crcut Output ha hunt tplgy Shrt-crcut the utput nde. Mdfed utput crcut nput ha ere tplgy Bac aplfer wthut feedback Open-crcut the nput lp. quvalent crcut f dfed feedback aplfer 9 r pcture (c) we get : f β f 1 plfer wthut feedback OL and β where g OL and gr r r r r - quvalent crcut f dfed feedback aplfer 10

6 plfer wth feedback and OL β β 1 g r r where r OL 1 β r β plfer wth feedback f we aued that << r we can wrte : β0 r β 0 when pprxatn nnunlateral feedback netwrk unlateral feedback netwrk ( 1 β0 ) β0 (auptn) r ( 1 β0 ) when ( 1 β ) 0 See Mllan, Grabel table

7 plfer wth feedback Dand Dead yte pedance D D r 13 nput ha Sere tplgy plfer wth feedback Dand OC Open crcut the nput : 0when OC SC Shrt crcut the nput : g when 0 SC g ( 1 g ) r β r 0 pprxatn ( 1 β0 ) β0 unlateral feedback netwrk ( 1 β ) r 0 See Mllan, Grabel table

8 Output ha Shunt tplgy plfer wth feedback ODand O Dead yte pedance OD OD r 15 Output ha Shunt tplgy plfer wth feedback ODand O SC Shrt crcut the utput : 0when 0 SC 0 OC Open crcut the utput : β r r OC 0 when β0r0 r O r r 1 β [ β 0r ( r )] 0 when r >> ( r ) β0 16

9 pprxate analy f a hunt-trple n general, practcal aplfer have tw r re tage. bplar hunt-trple feedback aplfer eedback netwrk xaple f analy f aplfer havng everal tage Hgh cled-lp gan Hgh return rat nput: Z Q1 Q2 Current cparn SHUN tplgy C1 C 2 Q 3 nternal aplfer Output: C3 L ZO ltage aplng SHUN tplgy - hree Cn-etter tage Lcal feedback Glbal feedback he nternal three-tage aplfer can be deled a a ngle equvalent aplfer. r r r Z 1 C3? r b1 S r r Z L 17 pprxate analy f a hunt-trple xaple f analy f aplfer havng everal tage bplar hunt-trple feedback aplfer eedback netwrk ltage gan f the frt (nput) tage : Z Q Q 1 2 C1 C 2 nternal aplfer Q 3 C3 L ZO - v β01 r r 1 C1 b1 S r r Z L r r r 1 r b1 1 ( r r ) he unladed vltage gan f the nput tage (frt tage). 1 v β r r b1 01 C1 ( r 1 rb1 ) β01c1 1 b1 18

10 pprxate analy f a hunt-trple xaple f analy f aplfer havng everal tage S r r Z L tal gan (tranpedance) f cntrlled urce : Z β 01 C1 v2 v3 reeber lad effect 19 pprxate analy f a hunt-trple xaple f analy f aplfer havng everal tage he apprxate del f the bac aplfer (hunt-trple) wthut feedback eedback reved, but nt ladng effect f. Mdfy nput de: Output ha hunt tplgy Mdfy Output de: nput ha hunt tplgy Shrt crcut utput Shrt crcut nput S r r S r r Z L Z L 20

11 pprxate analy f a hunt-trple xaple f analy f aplfer havng everal tage he apprxate del f the bac aplfer (hunt-trple) wthut feedback OL eedback reved, but ladng effect f n the nput and utput crcut ncluded. S r r Z L S r r Z L r r Z L OL Z where r L L r L L 21 pprxate analy f a hunt-trple xaple f analy f aplfer havng everal tage K X t21x t22x (Mllan 12-23) K X X X 0 t t See a General naly f eedback plfer 0 0 S r r Z L K X X X 22

12 pprxate analy f a hunt-trple xaple f analy f aplfer havng everal tage return rat K L OL Z Z L L r r r L r L 1 See a General naly f eedback plfer OL 1 D 1 K K 1 when dead yte gan D very lw 23 he nd f Part 12 24