FEEDBACK AMPLIFIERS. β f

Transcription

1 FEEDBC MPLFES X - X X X * What negatve eedback? ddng the eedback gnal t the nput a t patally cancel the nput gnal t the ample. * What eedback? Takng a ptn the gnal avng at the lad and eedng t back t the nput. * Den t th educe the gan? Ye, th the pce we pay ung eedback. * Why ue eedback? Pvde a ee benet, uch a mpved bandwdth, that utwegh the ct n lt gan and nceaed cmplexty n ample degn. * Q. Why d yu thnk that th type eedback called NEGTE?

2 Feedback mple naly X X X X X X X X X by gven eedback wth gan ample The uce the m gnal the X ample bac the t gnal nput net the X whee X X X gan vltage g e gan ample the whee X X act eedback the called whee X X <,.., X X X X -

3 dvantage Negatve Feedback * Gan deentvty - le vaatn n ample gan wth change n (cuent gan) tant due t dc ba, tempeatue, abcatn pce vaatn, etc. * Bandwdth extenn - extend dmnant hgh and lw equency ple t hghe and lwe equence, epectvely. L H H L * Ne eductn - mpve gnal-t-ne at * mpve ample lneaty - educe dttn n gnal due t gan vaatn due t tant Dadvantage Negatve Feedback L gan, may eque an added gan tage t cmpenate. dded cmplexty n degn 3

4 Bac Type Feedback mple * Thee ae u type eedback ample. Why? Output ampled can be a cuent a vltage Quantty ed back t nput can be a cuent a vltage Fu pble cmbnatn the type utput amplng and nput eedback * One patcula type ample, e.g. vltage ample, cuent ample, etc. ued each ne the u type eedback ample. * Feedback act a deent type quantty, e.g. vltage at, etance, cuent at cnductance, each eedback cnguatn. * Bee analyzng the eedback ample pemance, need t tat by ecgnzng the type cnguatn. * Temnlgy ued t name type eedback ample, e.g. See-hunt Ft tem ee t natue eedback cnnectn at the nput. Secnd tem ee t natue amplng cnnectn at the utput. 4

5 Bac Type Feedback mple See - Shunt Shunt - See See - See Shunt - Shunt 5

6 Methd Feedback mple naly * ecgnze the eedback ample cnguatn, e.g. See-hunt * Calculate the apppate gan the ample, e.g. vltage gan. Th nclude the ladng eect the eedback ccut (me cmbnatn et) n the ample nput and utput. * Calculate the eedback act * Calculate the act and make ue that t : ) ptve and ) dmennle * Calculate the eedback ample gan wth eedback ung * Calculate the nal gan nteet deent m the gan calculated, e.g. Cuent gan vltage gan gnally detemned. * Detemne the dmnant lw and hgh equency ple the gnal ample, but takng nt accunt the ladng eect the eedback netwk. * Detemne the nal dmnant lw and hgh equency ple the ample wth eedback ung ( ) H H L L 6

7 See-Shunt Feedback mple - deal Cae Bac mple * ume eedback ccut de nt lad dwn the bac ample,.e. den t change t chaactetc Den t change gan Den t change ple equence bac ample Den t change and Feedback Ccut * F the eedback ample a a whle, eedback de change the mdband vltage gan m t * De change nput etance m t ( ) Equvalent Ccut Feedback mple * De change utput etance m t * De change lw and hgh equency 3dB equence H ( ) H L L ( ) 7

8 8 See-Shunt Feedback mple - deal Cae Mdband Gan nput etance Output etance t t t t t t t t t t t t and But 0

9 Pactcal Feedback Netwk * Feedback netwk cnt a et et Smplet cae (nly cae cndeed hee) n geneal, can nclude C and L (nt cndeed hee) Tant metme ued (gve vaable amunt eedback) (nt cndeed hee) * Feedback netwk needed t ceate eedback gnal at nput (deable) * Hw d we take thee ladng eect nt accunt? * Feedback netwk ha paatc (ladng) eect ncludng: * Feedback netwk lad dwn ample nput dd a nte ee etance Pat nput gnal lt ac th ee etance (undeable), educed * Feedback netwk lad dwn ample utput dd a nte hunt etance Pat utput cuent lt thugh th hunt etance nt all utput cuent delveed t lad L (undeable) 9

10 See-Shunt Feedback mple - Pactcal Cae * Feedback netwk cnt a et et * Thee et have ladng eect n the bac ample,.e they change t chaactetc, uch a the gan * Can ncpate ladng eect n a mded bac ample. Bac gan ample becme a new, mded gan (ncpate ladng eect). * Can then ue eedback analy m the deal cae. ( ) ( ) 0

11 See-Shunt Feedback mple - Pactcal Cae Summay Feedback Netwk naly

12 Example - See-Shunt Feedback mple * Tw tage ample * Each tage a CE ample * Tant paamete Gven: 50 * Cupled by capact, dc baed epaately * DC analy: DC analy each tage can be dne epaately nce tage ae lated (dc we) by cuplng capact. m g C C 0.94, m 36 m/, T.4 gm m g C C.85, m 7 m/, T 0.7 gm

13 Example - See-Shunt Feedback mple * edaw ccut t hw Feedback ccut Type utput amplng (vltage n th cae ) Type eedback gnal t nput (vltage n th cae ) _ 3

14 Example - See-Shunt Feedback mple nput Ladng Eect h Output Ladng Eect 0 h mple wth Ladng Eect 4

15 Example - See-Shunt Feedback mple * Cntuct ac equvalent ccut at mdband equence ncludng ladng eect eedback netwk. * nalyze ccut t nd mdband gan (vltage gan th ee-hunt cnguatn) 5

16 6 Example - See-Shunt Feedback mple Mdband Gan naly db db g g m g m g m m C m x C m lg 0 ) ( / 36 0 nce / 7

17 Mdband Gan wth Feedback * Detemne the eedback act X X * Calculate gan wth eedback v 449(0.0) 9.4 * Nte ( db) 0lg dB v > 0 a neceay negatve eedback v lage thee gncant eedback. F v 0, thee almt n eedback. Can change and the amunt eedback by changng and/. NOTE: Snce v >> (0.0) (0.0) 9.4 ( db) 0lg dB

18 nput and Output etance wth Feedback * Detemne nput and utput etance wth ladng eect eedback netwk. S B C * Calculate nput and utput etance the cmplete eedback ample. ( ) 0.5 [ 449(0.0) ]

19 Equvalent Ccut See-Shunt Feedback mple S 43. ( db) 0lg dB ( ) * ltage gan ample * Mded vltage gan, nput and utput etance ncluded ladng eect eedback netwk ncluded eedback eect eedback netwk nclude uce etance eect * Sgncant eedback,.e. v lage and ptve 449(0.0) 9.4 ( db) 0lg dB

20 See-See Feedback mple - deal Cae ltage edback t nput Output cuent amplng * Feedback ccut de nt lad dwn the bac ample,.e. den t change t chaactetc Den t change gan Den t change ple equence bac ample Den t change and * F th cnguatn, the apppate gan the TNSCONDUCTNCE GN C / * F the eedback ample a a whle, eedback change mdband tancnductance gan m C t C C C C ( ) * Feedback change nput etance m t * Feedback change utput etance m t C * Feedback change lw and hgh equency 3dB equence L H ( C ) H L ( ) C C 0

21 See-See Feedback mple - deal Cae Gan (Tancnductance Gan) C C C C C C nput etance - C Output etance C t C t t C t C t t t t and But 0

22 See-See Feedback mple - Pactcal Cae * Feedback netwk cnt a et et * Thee et have ladng eect n the bac ample,.e they change t chaactetc, uch a the gan Feedback act gven by * Can ncpate ladng eect n a mded bac ample. Gan C becme a new, mded gan C. * Can then ue analy m deal cae C H C ( ) C C H L ( ) ( ) C L ( ) C C

23 See-See Feedback mple - Pactcal Cae Fnd m / 3

24 See-See Feedback mple - Pactcal Cae * Mded bac ample (ncludng ladng eect eedback netwk) * Can nw ue eedback ample equatn deved C H C ( ) C C H L ( ) ( ) C L ( ) C C * Nte C the mded tancnductance gan ncludng the ladng eect S and L. and ae mded nput and utput etance ncludng ladng eect. 4

25 Example - See-See Feedback mple Nte: Bang et each tage ae nt hwn mplcty n the analy. * Thee tage ample * Each tage a CE ample * Tant paamete Gven: 3 00, x x x3 0 * Cupled by capact, dc baed epaately * DC analy (gven): C C C m, g m g m 3 g m m, g m, g g m m m C T C C3 T T 3 m/, 39 m/, 56 m/, 5

26 Example - See-See Feedback mple * edaw ccut t hw: Feedback ccut Type utput amplng (cuent n th cae ) Cllect et cnttute the lad c Emtte cuent e b {/ } c c Type eedback gnal t nput (vltage n th cae ) c3 ltage edback t nput Output cuent amplng 6

27 Example - See-See Feedback mple nput Ladng Eect Output Ladng Eect 0 0 z E [ ] F 0. [ ] E z E [ ] F 0. [ ] E 7

28 Example - See-See Feedback mple ltage edback t nput Output cuent amplng edawn bac ample wth ladng eect, but nt eedback. 8

29 Example - See-See Feedback mple C3 E3 C3 * Cntuct ac equvalent ccut at mdband equence ncludng ladng eect eedback netwk. * nalyze ccut t nd MDBND GN (tancnductance gan C th ee-ee cnguatn) C S 9

30 30 Example - See-See Feedback mple Mdband Gan naly [ ] [ ] m x m g m g m g g g g m g g C S m C m m C m m m m m C /.5 0 / / / / ) ( / S Nte cnventn n nt the utput the lat tage the ample. 3

31 Feedback Fact and Mdband Gan wth Feedback * Detemne the eedback act X E E E X E E 0.0 F Ω E * Calculate gan wth eedback C C C 0.5/ (Ω) 46 C C 0.5/ 0.5 / (Ω) 0.5 / / 83 m/ E ( ( F F F E ) ( E E E ) E E E ) E * Nte C > 0 a neceay negatve eedback and dmennle C lage thee gncant eedback. ha unt etance (hm); C ha unt cnductance (/hm) Can change and the amunt eedback by changng E, F and/ E. Gan lagely detemned by at eedback etance E E F C 0. (0. ) E E m/ 3

32 nput and Output etance wth Feedback (g m ) * Detemne nput and utput etance wth ladng eect eedback netwk. ( gm ) * Calculate nput and utput etance the cmplete eedback ample ( ) C [ 0.5 / (Ω)] ( 47) 3.6MΩ 3 C ) ( C 3

33 ltage Gan Tancnductance Feedback mple * Can calculate vltage gan ate we calculate the tancnductance gan! ( db) 0lg C3 ( 49.8) 34dB * Nte - can t calculate the vltage gan a llw: ume Fnd Calculate Calculate Magntude vltage C3 Ω gan wth C3 C3 ( 0.5 / ) C 600Ω(0.083 / ) 49.8 / 4 5 (.3x0 / ).48x0 Ω ( Nte th ha unt (t huld nt! ) by de C3 eedback m C 600Ω magntude and unt 4.3x0 / ae 4.3x0 / 5.48x0 Ω wng! Ω Cect vltage gan the ample wth eedback! and a negatve gn) Wng vltage gan! 33

34 Equvalent Ccut See-See Feedback mple * Tancnductance gan ample / * Feedback mded gan, nput and utput etance ncluded ladng eect eedback netwk ncluded eedback eect eedback netwk * Sgncant eedback,.e. C lage and ptve C C m 83 / ( C ) 3.3 S C ( C ) C 3C 49.8 / MΩ C C 0.5/ (Ω) 46 C 0.0 C C C 84 m/ 34

35 Shunt-Shunt Feedback mple - deal Cae * Feedback ccut de nt lad dwn the bac ample,.e. den t change t chaactetc Den t change gan Den t change ple equence bac ample Den t change and * F th cnguatn, the apppate gan the TNSESSTNCE GN / * F the eedback ample a a whle, eedback change mdband tanetance gan m t * Feedback change nput etance m t * Feedback change utput etance m t ( ) * Feedback change lw and hgh equency 3dB equence H ( ) ( ) H L L ( ) 35

36 36 Shunt-Shunt Feedback mple - deal Cae Gan nput etance Output etance and But 0 _ 0

37 Shunt-Shunt Feedback mple - Pactcal Cae * Feedback netwk cnt a et et * Thee et have ladng eect n the bac ample,.e they change t chaactetc, uch a the gan * Can ue y-paamete equvalent ccut eedback netwk Feedback act gven by * Can ncpate ladng eect n a mded bac ample. Gan becme a new, mded gan. * Can then ue analy m deal cae H ( ) ( ) ( ) H L L ( ) 37

38 Shunt-Shunt Feedback mple - Pactcal Cae 38

39 Example - Shunt-Shunt Feedback mple 0 g BE, actve C * Sngle tage CE ample * Tant paamete. Gven: 00, x 0 * N cuplng emtte bypa capact * DC analy: m 70µ 0 ( ) ( B 0.07 m) ( ) 0.07 m) 4.7 ( 0.07 m) B m ( ( 0( 4.7 ) 47 ) m 6 µ 5.6 m C 63 m/ T B 4.7 B C B 47 C B 0.07 m) B B B m 0.07 m B 0.07 m ( m) g 63 m/.6.6 m 39

40 Example - Shunt-Shunt Feedback mple * edaw ccut t hw Feedback ccut Type utput amplng (vltage n th cae ) Type eedback gnal t nput (cuent n th cae ) 40

41 Example - Shunt-Shunt Feedback mple nput Ladng Eect Output Ladng Eect F 47 F 47 4

42 Example - Shunt-Shunt Feedback mple Ognal Feedback mple Mded mple wth Ladng Eect, but Wthut Feedback Nte: We cnveted the gnal uce t a Ntn equvalent cuent uce nce we need t calculate the gan 4

43 Example - Shunt-Shunt Feedback mple * Cntuct ac equvalent ccut at mdband equence ncludng ladng eect eedback netwk. * nalyze ccut t nd mdband gan (tanetance gan th hunthunt cnguatn) 43

44 44 Example - Shunt-Shunt Feedback mple Mdband Gan naly m g g F S S F C m F C m / / 63

45 Mdband Gan wth Feedback * Detemne the eedback act X X 0.0 m/ 47 F _ * Calculate gan wth eedback * Nte < 0 and ha unt m/, < 0 and ha unt C > 0 a neceay negatve eedback and dmennle C lage thee gncant eedback. Can change and the amunt eedback by changng F. 0.0m / ( 350 ) Gan detemned pmaly by eedback etance F ( / ) 47 F Nte: The dectn alway nt the eedback netwk! 45

46 nput and Output etance wth Feedback * Detemne nput and utput etance wth ladng eect eedback netwk. S F C F * Calculate nput and utput etance the cmplete eedback ample. ( ) ( )

47 ltage Gan Tanetance Feedback mple * Can calculate vltage gan ate we calculate the tanetance gan! 4 4. / 0 ( db) 0lg( 4.).5 db Cect vltage gan * Nte - can t calculate the vltage gan a llw: ume Fnd Calculate Calculate Magntude vltage ( 0.0 m / )( 35 / ) 0.74 m / ( Nte th ha unt; t huld nt! ) gan wth by nealy eedback a act 35 / m ve and unt ae 35 / 0.74m / wng! 0 / (?) Wng vltage gan! 47

48 Equvalent Ccut Shunt-Shunt Feedback mple * Tanetance gan ample / * Feedback mded gan, nput and utput etance ncluded ladng eect eedback netwk ncluded eedback eect eedback netwk * Sgncant eedback,.e. lage and ptve 4 S ( ) ( ) m / ( 350) 7.4 S 4. / 47 48

49 Shunt-See Feedback mple - deal Cae Cuent eedback Cuent amplng * Feedback ccut de nt lad dwn the bac ample,.e. den t change t chaactetc Den t change gan Den t change ple equence bac ample Den t change and * F th cnguatn, the apppate gan the CUENT GN / * F the eedback ample a a whle, eedback change mdband cuent gan m t * Feedback change nput etance m t * Feedback change utput etance m t * Feedback change lw and hgh equency 3dB equence L H ( ) H L ( ) 49

50 50 Shunt-See Feedback mple - deal Cae Gan nput etance Output etance 0 and But 0

51 Shunt-See Feedback mple - Pactcal Cae * Feedback netwk cnt a et et * Thee et have ladng eect n the bac ample,.e they change t chaactetc, uch a the gan Feedback act gven by * Can ncpate ladng eect n a mded bac ample. Gan becme a new, mded gan. * Can then ue analy m deal cae H ( ) H ( ) L L ( ) ( ) 5

52 Shunt-See Feedback mple - Pactcal Cae 5

53 Example - Shunt-See Feedback mple * Tw tage [CECE] ample * Tant paamete Gven: 00, x 0 * nput and utput cuplng and emtte bypa capact, but dect cuplng between tage * Capact n eedback cnnectn emve m DC ba * DC ba tw tage cupled (ba ne aect the the) 53

54 54 DC Ba naly m g m m g m m T C m B C E TH BE TH B B B B TH B B TH.9 / / )0.87 ( µ µ m g m m g m m m T C m B C E B E B E E BE C B C C C 3.3 / / µ µ 0 00 Gven : x x C B (neglectng B ) (<< C 870 )

55 Example - Shunt-See Feedback mple * edaw ccut t hw Feedback ccut Type utput amplng (cuent n th cae ) Type eedback gnal t nput (cuent n th cae ) ut ut 55

56 Example - Shunt-See Feedback mple ut nput Ladng Eect 0 Output Ladng Eect F F E

57 Example - Shunt-See Feedback mple mple wth Ladng Eect but Wthut Feedback 57

58 58 Example - Shunt-See Feedback mple Mdband Gan naly [ ] [ ] / / / m m g g g g g m g g ut B S S m C m C m m m m m c L C C c ut c c ut ut ut C

59 Mdband Gan wth Feedback * Detemne the eedback act * Calculate gan wth eedback 93( 0.5) 48 * Nte < 0 and < 0 X X E ( ) E ( db ) 0 lg db > 0 a neceay negatve eedback and dmennle lage thee gncant eedback. Can change and the amunt eedback by changng F. Gan detemned by eedback etance E - E ( ) ( ) E E E E E E E

60 nput and Output etance wth Feedback * Detemne nput and utput etance wth ladng eect eedback netwk. S B C L * Calculate nput and utput etance the cmplete eedback ample. ( ) ) (49) ( 60

61 ltage Gan Cuent Gan Feedback mple * Can calculate vltage gan ut L db ( db) 0lg * Nte - can t calculate the vltage gan a llw: ume Fnd Calculate ( 0.5)( 9.3 / ) Calculate vltage gan wth eedback m Magntude by nealy a act ten! L L L ut ( 93) ( ) L 9.3 / 0 ( 4.) 9.3 / / / 6

62 Equvalent Ccut Shunt-SeeFeedback mple * Cuent gan ample / * Feedback mded gan, nput and utput etance ncluded ladng eect eedback netwk ncluded eedback eect eedback netwk * Sgncant eedback,.e. lage and ptve ( ) S 3.9 ) ( ( db ) 93( 0.5) lg db E E 4.0 6

63 Summay Feedback mple naly X X X X L H L ( ) ( ) H * denty the ample cnguatn by: Output amplng ee cnguatn hunt cnguatn Feedback t nput hunt cnguatn ee cnguatn * Calculate ladng eect eedback netwk On nput On utput * Calculate apppate mdband gan (mded by ladng eect eedback netwk) * Calculate eedback act. * Calculate mdband gan wth eedback. 63

64 Summay Feedback mple naly 64

65 Feedback mple Stablty ( ) L L ( ) ( ) and n ce ( ) { ( ) ( )} { ( ) ( )} jφ e ( ) φ ( ) tan m e ( ) ( ) ( ) ( ) e H 80 j H 0 mple becme untable (cllate) at me equency we have adan * Feedback analy Mdband gan wth eedback New lw and hgh 3dB equence L H ( ) H L ( ) Mded nput and utput etance, e.g. ( ) * mple equency chaactetc M FH FL * Feedback ample gan * Dene Lp Gan a Magntude Phae φ m tan e jφ ( ) e { } { } 65

66 (db) Feedback mple ntablty * mple wth ne ple Phae ht the maxmum Cannt get phae ht. N ntablty pblem * mple wth tw ple 0 db Phae ht the maxmum φ ( ) Geneal m Magntude plt Geneal m Phae plt 80 ( ) j ( ) j HP HP HP Can get phae ht! * F tablty analy, we dene tw mptant equence whee magntude ge t unty (0 db) 80 whee phae ge t -80 ntablty pblem 80 ( ) 80 j ( ) ( ) ( ) ( ) 66

67 Gan and Phae Magn (db) 80 0 db Gan magn -30 φ ( ) * Gan and phae magn meaue hw a ample m the ntablty cndtn * Phae magn Phae magn φ Example Phae 35 * Gan magn magn φ 0 φ( ) ( ) φ( ) 0 ( 80 ) 45 Gan magn Example Gan magn 0 db ( ( ) ( ) ( ) ( ) db) 30 db Phae magn Φ( ) Φ( 80 ) * What ae adequate magn? Phae magn 50 0 (mnmum) Gan magn 0 db (mnmum) 67

68 Numecal Example - Gan and Phae Magn (db) 3.5 db Ple Ple ( db) 3.5 db Phae Sht (degee) Gan magn 5 j j 5 6 8x0 3x0 Fm plt magntude and phae 6x0 φ ad / 0 ( ) 40 and φ( ) φ phae magn ( ) φ( ) 6 80 and ( 80 3x ) 40 ad / 0 Phae magn 80 ( ) 0 db ( ) ( gan magn and 80 ( ) 0 ( 8 80 ) 8 db) 8 db db Nte that the gan and phae magn depend n the eedback act and the amunt eedback and eedback et. * Dectly thugh the value. * ndectly nce the gan and ple equence ae nluenced by the eedback et, e.g. the ladng eect analyzed pevuly. 68

69 / (db) 0 0 φ mple Degn dequate Gan and Phae Magn (db) ( 80 ) 0 db Geneal m Magntude plt Gan magn 80 Geneal m Phae plt Phae magn 80 Φ( ) Φ( 80 ) * Hw much eedback t ue? What? * change mean edng ( ) plt! * thee an altenate way t nd the gan and phae magn? YES Plt magntude and phae gan ( ) ntead ( ) v equency Plt hzntal lne at / n magntude plt (nce ndependent equency) Why? t nteectn / wth ( ), S th nteectn pnt gve the value whee! Then we can nd the gan and phae magn a bee. * nt adequate magn, pck anthe value, daw anthe / lne and epeat pce. * Nte: a meaue the amunt eedback. Lage mean me eedback. ecall 0, we have NO eedback X X 0 X 0 nceae, we have me eedback 69

70 φ ( ) (db) 43.5 db / (db) Gan magn ( 80 ) Example - Gan and Phae Magn ltenate Methd 80 Fm 6x0 φ φ 50 ( ) 0. ad / 0 ( ) 40 and φ ( ) phae ( ) φ ( ) ( db) j 5 8x0 ( db) 0 lg0 0 plt 6 magn 80 magntude and db j 3x and ( 80 db phae 3x ) 40 ad / 0 Phae magn / ( ) 0 db and gan magn / ( ) ( 80 ( 80 ) 8 db ) 0 ( 8 db) 8 db Thee ae the ame eult a bee the gan and phae magn. 70

71 Summay Feedback mple Stablty ( ) * Feedback ample ae ptentally untable Can beak nt cllatn at a patcula equency whee L L H H Ocllatn ntablty a degn pblem any ample wth tw me hgh equency ple. Th the cae LL ample nce each bpla MOSFET tant ha tw capact and each capact gve e t a hgh equency ple! ( ) ( ) and n ce ( ) { ( ) ( )} { ( ) ( )} jφ e ( ) φ ( ) tan m e ( ) ( ) ( ) ( ) e 80 j adan * Need t degn eedback ample wth adequate aety magn Mnmum gan magn 0 db Mnmum phae magn 50. djut by vayng ze. Smalle, the lage the amunt eedback. 0 7