Output Stages and Power Aplfers Output stages wth a low output resstance can delver the output voltage to the load wthout loss of gan. arge sgnal aplfer are used to drve a CT, a loud speaker, a servootor, etc. power ap. = large sgnal ap Power ap.can delver large voltage or current or a large aount of power. Theral consderatons are portant for power ap. 3 - Electroncs(3), 03
arge-sgnal Aplfers C s the quescent collector current (DC sgnal). c s the nstantaneous varaton fro C. (Sall sgnal) c and c are the rs values of v c and c. s the peak of snusodal current swng. CC C ax C B B C 0 Q B B3 BB n n C 0 ax CC v c t 3 - Electroncs(3), 03
arge-sgnal Aplfers (Cont.) c c ax ax n n Assung perfect lnearty,.e. no nonlnear dstorton) Output power P c c ( c ax n )( 8 ax n ) 3-3 Electroncs(3), 03
Haronc Dstorton Nonlnear Dynac transfer characterstc s not a straght lne. Sall sgnal arge sgnal Both have nonlnearty probles. nd haronc dstorton nonlnear relatonshp between b and c s assued. 3-4 Electroncs(3), 03
Haronc Dstorton(Cont.) b c c C G b b G cost b G b cost G G b cost G B0 B cost B B C c C 0 where G & G are constant. cos t b G cos t B cost B b b cos t cos t a. DC level s changed. b. nd haronc dstorton s ntroduced. 3-5 Electroncs(3), 03
Haronc Dstorton (Cont.) B nd haronc dstorton D B nter-odulaton For cosω t cosω c contans,,,,, nd haronc dstorton Hgher order haronc dstorton =G +G +G + 3 c b b 3 b c c 0 3 3 D =, D 3 =, B B where D n represents the nth haronc dstorton HD n nter-odulaton = +B +B cos ωt+b cos ωt+b cos3 ωt+ B b b b B t 3-6 Electroncs(3), 03
3-7 Electroncs(3), 03 Total Haronc Dstorton(THD) Power delvered at the fundaental frequency s Total power output s B P... D D D THD P... D D... B B B P 4 3 3 3
Aplfer Classfcaton Class A Output ~ X nput X Class B Output ~ nput BE 3-8 Electroncs(3), 03
Aplfer Classfcaton (Cont.) Class AB Output BE ~ nput Class C Output BE ~ nput 3-9 Electroncs(3), 03
Power Converson Effcency portant under. lted source of power. (e.g. n a satellte). axu power-dsspatng consderaton. Converson effcency sgnal power delvered to load dc power suppled to output crcut Class A aplfer wth c and v c output v C c c η C snω t snω t CC c C 00% 50 CC C % 00% 3-0 Electroncs(3), 03
Power Converson Effcency (Cont.) Sall sgnal,.e.(. 0 ) are sall. statc power consupton CC C even no exctaton Maxu sgnal,.e. = C, =0.5 CC 5% Class A operaton s a poor choce for power aplfcaton. C 3 - Electroncs(3), 03
Class B OPAMP Class B Push-Pull Aplfer Q CC C Dynac transfer characterstc O ~ Q CC CC C 0 0 B B B B ω t B v ~ C Exctaton ω t 3 - Electroncs(3), 03
Class B Push-Pull Aplfer (Cont.) Effcency of Class B push-pull Output power DC power (suppled by CC ) dc P Effcency η For π π P o CC Po π 00% P 4 η CC Two transstors for push-pull CC ax 00% 78.5% No statc power consupton under zero exctaton π 4 00% 3-3 Electroncs(3), 03
Class B Push-Pull Aplfer (Cont.) Average power dsspated n the class B stages. CC P P P A (Two transstors push-pull) Dfferentatng Eq.(A) wth respect to and equatng the dervatve to zero gves the that results n axu P D D For π o CC π P CC D(ax) P π o,ax P D P D(ax) CC CC power output η 50% η 78.5% π CC /π CC CC 3-4 Electroncs(3), 03
Dstorton n the Class B Push-Pull Stage CC Q O Q Haronc dstorton CC For atched devces Q & Q and are dentcal except shfted n phase by 80 ( ω t) C C B B 0 B cos ω t B ( ω t π) 0 B cos ω t B cos ω t B cos3 ω t cos ω t B cos3 ω t (B cos ω t B cos3 ω t ) 3 3 3 3-5 Electroncs(3), 03
Dstorton n the Class B Push-Pull Stage (Cont.) Even-order haronc dstortons have been elnated. f the -s of Q &Q are not dentcal, then evenorder haronc dstortons are expected. Crossover dstorton Wll be dscussed later. 3-6 Electroncs(3), 03
Output Stages deal output stages Supply external load current ow output pedance arge output swng CC EE deally Coonly used copleentary etter follower Each transstor s on for only half the te. 3-7 Electroncs(3), 03
Crossover dstorton Output Stages (Cont.) + CC o Q Q o Q (cut off) CC - CE(sat) - BE(on) BE(on) Q (sat) Q (cut off) o t Q (sat) - CC + CE(sat) - CC 3-8 Electroncs(3), 03
Output Stages (Cont.) Elnaton of crossover dstorton CC O bas CC - BE - CE(sat) D Q - BE(ON) D O Q - CC CE(sat) CC 3-9 Electroncs(3), 03
Elnaton of Crossover Dstorton of 74-Type OPAMP Output stage CC CC Q 3A Q 4 Q 9 6 o 40k Q 8 7 o Q 0 Q 3 EE EE 3-0 Electroncs(3), 03
Elnaton of Crossover Dstorton of 74-Type OPAMP (Cont.) Crcut Dagra CC 5 Q Q 9 Q 8 Q 3B Q 3A Q 9 Q 5 Q 4 6 7 5 39k n Q Q Q3 4 Q n C C 30pF 0 40k Q 8 Q 3 Q 7 Q 0 7 Q 6 Q EE Q 0 5 4 5k Q 7 Q5 Q6 k 3 50k k Q 9 50k Q 7 8 00 Q 4 50k 3 - Electroncs(3), 03
Classcal CMOS Class AB Output Stage Q N and Q P are source followers Q and Q are dode-connected elnate crossover dstorton Quescent current Q D D GG GG BAS BAS slarfor assuek kn' k p GS n Q GSN ' N W GS tn ' W SG tp SG andq 0.5 k ' W k ' W n p 0.5 k ' W k ' W n p W k ' W k ' W k ' W p and n p SGP P, tn tn tp tp BAS Q n BAS v n Q p + DD 0.5 0.5 W n W 3 - Electroncs(3), 03 + GG v o Q - Q P - SS Q p Q N BAS
estrcted Output Swng of Classcal Class AB vo v ax DD O Oax where v slarly, v On v O ON where O OP BAS : : O DD SS of O Q BAS P O vgsn BAS tp tn v v ON : n. voltage across current source of Q when t s supplyng O N OP ax : n. voltage across the transstor supplyng v when snkng the ax. + DD BAS v Q + GG v o Q - Q P (not Q N - SS shown) One drawback of classcalcmos classab output the restrctedoutput swngrange stages 3-3 Electroncs(3), 03
CMOS Class AB Utlzng Coon-Sources Allowable range of v O voax DD vop von SS von output swng range s ncreased Hgh output resstance out n Negatve seres-shunt feedback reduce the out of the aplfer vo v f the loop gan s large out // v out p μ - + - μ + DD Q P DP DN Q N DD Q P Q N - SS v o v o - SS OUT 3-4 Electroncs(3), 03
out educton by Seres-Shunt Feedback v The top half crcut - + μ DD Q P outp v o of v the A crcut - + μ Q P v o the β crcut f + - + O - A of outp out gp ( rop // ), o A g outp // of outn o p // r op ( r op // r // op r op // gp // g p g n ) g g p of p g 3-5 Electroncs(3), 03 n
oltage Transfer Characterstc n the quescent state v 0 and vo 0 DP Q k p ' W O p DN Q kn' W O n assue Q and Q are atched.e. k Q p ' W k ' W P k p O n N n k DD - SGP - SS + GSN DD + SGP - Q P μ - + - 0 + - μ + + GSN - Q Q Q N - SS 0 3-6 Electroncs(3), 03
3-7 Electroncs(3), 03 O Q p Q O O Q O Q O O DN DP O O O Q DN O O Q O O O O O DP g g g v v v v v v v v v v v v k v v k 4 4 4 ) ( ) ( Gan error snce Gan error slarly, oltage Transfer Characterstc (cont.) When v s appled Q P Q N v o DD - SS - + μ - + μ DP DN + - SGP ( DD SGP ) +μ(v o -v ) + - GSN (- SS + GSN ) +μ(v o v ) v
Error aplfers gan µ larger µ Desgn Trade-offs saller gan error and out saller µ Q s ore nsenstve to the nput offset voltages of the error aplfers Quescent current Q larger Q saller crossover dstorton, gan error, and out saller Q less power dsspaton 3-8 Electroncs(3), 03
Theral Desgn Consderatons C power aplfer Capable of delverng large power to external load. Exaple : A 5-W audo aplfer 0k 6 M384 4 3 C 3 0.uF 8 C 5uF C 0.uF 500μF speaker 8 The axu possble power converson effcency s about 75% (Class B or AB).e. for every 3-W output, W s dsspated wthn the aplfer. 3-9 Electroncs(3), 03
Theral Desgn Consderatons (Cont.) P D T TT J(ax) rreversble falure occurs where T J(ax) s the axu operatng juncton teperature of seconductor devce. Theral resstance q JC (between juncton and case) T T ΔT P θ J C unt: P D :Watt JC D q: 0 C/Watt JC 3-30 Electroncs(3), 03
Dsspaton Deratng Curve Exaple : N567 power transstor Maxu allowable dsspaton P D(ax) = 40W Dsspaton deratng curve θ JC 00 5 40.5 0 C power deratng factor W P D,(ax),W 40 00 75 50 5 0 50 00 50 00 Case teperature T C θ 0 JC 0.8W Exaple 3-7 and 3-8 of textbook T J ΔT JC ΔT CS C ΔT SA T A Chp (juncton) case heat snk 3-3 Electroncs(3), 03
Dsspaton Deratng Curve (Cont.) J : seconductor devce juncton C : case S : heat snk A : abent P D q jc q cs T J T jc T C T cs T S T J P D (θ JC θ CS θ SA ) T A q SA T sa T A 3-3 Electroncs(3), 03
Power FET Exaple : DMOS (Double-dffused MOS) Asyetrc source and dran. S and D ay not be nterchanged Conventonal Currently popular Source Gate Source Gate Dran P n Substrate n Source P n n Body n + n + p n + n - p - -substrate Current flow Dran 3-33 Electroncs(3), 03
araton on Class AB Confguraton Use of nput etter followers Hgh nput resstance CC Q 3 Quescent current n Q 3 and Q 4 s equal to that n Q and Q, f = and 3 = 4 0 Q CC CC c Q 3 4 Q 4 O CC 3 and 4 are sall and are ncluded to guard aganst the possblty of theral runaway due to teperature dfferences between the nput and output stage transstor. 3-34 Electroncs(3), 03
Copound Devces Darlngton confguraton. ncrease current gan. educe base current drve 3. Equvalent BE(eq.) = BE 4. Can be used for both NPN and PNP transstors Copound PNP confguraton. Used to prove PNP confguraton. Q s usually a lateral PNP havng low β ( 5 0) E E E E C C B B Q B B β ~ β β B Q B β ~ β β Q C C C C BE BE Q E BE E 3-35 Electroncs(3), 03
BE Multpler v Crcut ( Applcaton Exaple on DC evel Shftng CC 3 4 C C Q 3 Q 4 v o v o A O O For g BE 4 O BE ( 3 g BE BE BE ( ( 3 4 O & 4 ) 3 4 3 4 ) ) ) g BE g ( 3 3 4 g 4 4 )( g, A 4 ) 3-36 Electroncs(3), 03
BE Multpler (Cont.) Elnaton of crossover dstorton usng BE ultpler equvalent 3-37 Electroncs(3), 03
Class AB utlzng a Darlngton NPN and a Copound Bas s obtabed usng a BE ultpler BE ultpler s requred to provde 3 BE CC Q Q Q 5 O Q 3 Q 4 CC 3-38 Electroncs(3), 03
Class AB utlzng a Darlngton NPN and a Copound (Cont.) Short-crcut protecton BE5 C5 B C CC Q Q 3 Q 5 Q 4 E O E Q CC 3-39 Electroncs(3), 03
Class AB utlzng a Darlngton NPN and a Copound (Cont.) Theral shutdown T, Z BE Q absorbs bas current of OPAMP C CC Q Z Q CC 3-40 Electroncs(3), 03