CH 6 Part 2 Multistage Amplifiers

CH 6 Part 2 Multistage Amplifiers - 34/6 1", u /...

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Unformatted text preview: 34/6 1", u / 71112252 {91$}: [:79 P5. In "mos‘d‘, W's/offrwémmd a guy/e #ffi’flxrsér‘ Gave/745‘ «2:30, «A911: Ale. cal/e. 7g 4416-62! 7% afamrflcrfiém’ mpg awn/Adair; gc-éc firmmér I??7JI1(:-P'[‘ cmcmfi. r112“?! J1? comma-42% #4:] S-EWPgJ cor cascaded; ms 5:592:11. J' A genaraltzed Ihraa-staga amplifier cam, q, Q6” wand; 71:": cascfia/e. % lila’lnfra/uw/ 5%gx4' ti, RC‘ coo]: leéé agave/new; 3.. mesgmwr— c-awjplepé flmpo/IJCW-‘s 3- DIWC‘é’CWF/eCi fifty/b34955, R C ** Caugleal firing/I fillers, 23/2; )9 mscm’gaé RC"¢0UFLB&LJ FLUD-S7ZCE a. der1£l¢55 SJflCUIfi C 718156] MW .16: Liam; alga/)Wilydés tiff/sears 446%»; %‘{’7wmc)é&fj “PC” cw fléafi’UL (int/€65 \erm 75 Alas/"I W25:an 55 can :4: f (7 1 j caFrrCnlgt—s igfiflgm, $105159. [ Vac M 5;“ 50 *F' TF:Q5}{_ "Wm, .- R, *1: 43:2. §=I$¥§ - a 7"“: ‘ RQBI-Prm (‘1 3.33k+0.5k 62-, == 50 (QS’FIfi) a: 17351—6: 1‘."- ;_"_ '— . M.=~. ’ 1-D Tot 6C! 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Note that step-dovm transformers are employed between stages while a step-up transformer is connected to the source V}, The step~up transformer increases the signal level while the step-down transformer matches. as closely as possible, the loading of each stage to the output impedance of the preceding stage. This is done in an effort to be as close to meximum-powar-transfer conditions as possible. The effect of this match~ ing technique through the use ot‘ transformer coupling will be clearly demonstrated in the following analysis. Vcc 3 8V [le = E: 11411"? 1‘"? - + 5 : l (step—down) 4 kflEOnF —- — u- u- — 50oF E 1:91 Figure 9.10 Two-stage transformer-coupled transistor amphfien / Recall that a coupling capacitor was inserted to prevent any do levels of one stage from affecting the bias conditions of another stage“ The transformer provides this do isolation very nicely. The basic operation of this circuit is somewhat more eilicient than the RCcoupled transistors doc to the low dc resistance of the collector circuit of the transfermer— coupled system. The primary resistance of' the transformer is seldom more than a few ohms as compared to the large collector resistance RC of the RC—coupied system. This loWer dc resistance results in a lower dc pUWer loss under operating conditions. The efficiency, as determined by the ratio of the ac power out to the do poWer in, is therefore somewhat improved. There are some decided disadvantages, however, to the transformerrcoupled sys— tem. The most obvious is the increased size of'such a system (due to the transformers) compared to RC—coupled stages. The second is a poorer frequency response due to the newly introduced reactive elements (inductance of coils and capacitance between turns). A third consideration, frequently an important one, is the increased cost of the transformer-coupled (as compared to the RC—cnupled) system. 9.9 new nit/ergo. hm were = run-n “T he? = zonmv I Z. =— 0 has 3501mm Before we consider the ac response of the system. the fundamental equations related to transfonner action must be reviewed. For the configuration of Fig. 911. E = if} = c (Msformaticu ratio) (9-5) Vii Na L_m_3 I2 It a M) ’ Fl _ ' and i Z! 3 E122; l flit; a {:1 Blair: transient-rem which states, in words, that the input impedance of a transformer is equal to the turns ratio squared times the load impedance. Figure 9.12 Ccscaded transformer-coupled amplifim of Fig. 9.10 redrawn to determine the small-signal no response. For the ac response, the circuit of Fig. 9.10 will appear as shown in Fig. 9.12. For maximum power transfer the impedances 22 and 2; should be equal to the output impedance of each transistor: 2., E To a . This is one" .i system where the effect of ('0 must be considered. The hybrid parameters wiii therefore be employed in its solution” Applying 3 # a221, 24 2 c1212; : (5)22 k9 = 50 k9,. Z: is also 50 k9. since the input resistance to each stage (Zr and 23) is E G;- = 2 kn. Frequency considerations may not always permit a or Z; to be equal to To . For situations of this type 2; and Zr are usually made as close as possible to To in magnitude. Further analysis of the circuit of Fig. 9.12 results in _ N2 __ V: M Vi '— 4 V1 and {1 _ ~— g‘lzL 2 mice 42.4122) = wsocso muse km = _625 ' ”‘ ‘ or nr 2 to so that V2 = «4525 V; H eszswm reason N2 1 1 b t = .... 7. .. = .. _ =,_ 11 V; N11»; 5V: Sc 250cm) soon I - -—.—"". . — Sizn —(sc)(25 kn) It NF NS : and =.._.__.—_~.___.._.__._.c_ =m_ m- _ A”: w 2 kn 6 P3 ' so I»; =-—525 I»; a ~625(-soo Pg) m = 312.50 x 10m 1 1 primary winding Seconrinry winding with n=-5-Iq:-5~(312.so>< 103m and A”? = m 62.50 x 103 . . s E m "cum fig” 58 $3M? 3w m It rungs. : a fin.“ I. am {mom flame \1 9. efink?aflmmcmfihv+o+umtmmHWI a m \ on: H m a runwufi 1 .. Emmmlolmmtxaco H. a» + £2 Ilium» a bu 5 m E? 3,8 pm a. k ., a: u 3% “STE” #6- $3sz % r #3 mm»: H E anw gm .. 23 6H 7? NW A. . “NMH Q EIE am+mmi Elvin ‘ n .fisuxnmw. H u h? a“ $3.9. E Q. :8 V a 3.. Nu Awmux no.3 39.9 .S HUNG . 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SW Mafia 9...me Le *va Emmy: .‘TUQ W $55? bi w wwfifi \«SW w“.qu .mmNfiQ Emwmow \Wow MRK. yo gfiyw: {Sm \‘NQQQVM . MWcNfiwfikfit. REM uwowwlzao Qumnmz.» mks 9% www «Rim. %m G luau: #0.?» “5%th +m§~n§w J 1 Wm?“ Er: Armmwwfi.‘ Q. Sham GE» mac 5 O “.MQ Army wk d.an afifig .m N “EX rum n m "Ma k\\am 9&0 m .5 EEer 3 3% mug“ * Mm m .Q\ n IMQW+¢$M unutfl—awu M—uw a“ “BL... WL9+Q¢MWW Helm damuaflfiwmm km a .56 unmitlaum "H m SEN L immamm HQ 9. “WIN—“TAan mum Hgklfl ... firm "awn Q . «I lull] Nuggw MRS 1% “fifik ofiuwwumw Junk“ "Nam .5an 94m 102 358E TRANSACTIONS ON CIRCUITS AND SYSTEMS—4'. FWDAMEN‘I‘AL. THEORY AND APPUCATIONS. VOL as. NO 1. JWARY l999 Darlington’s Contributions to Transistor Circuit Design David A. Hodges, Fellow, IEEE (Invited Paper) IDNEY Darlington's name is well known to electronic circuit designers. He is credited with the discovery and initial demonstration in the early l950’s of what ever since has been known as the Burlington transistor pair, or simply the Burlington transistor or Burlington pair. This episode provides another example of Sidney's wide-ranging technical interests and his creativity addressed to the solution of real engineering problems. Early silicon transistors suffered from low values of common-emitter current gain ,6, and large variations of ,6 from sample to sample. 3 might range from 5 to 15 for good samples of silicon grown—junction transistors. Given these nonideal active elements. electronic circuit designers had difficulty designing circuits with reasonably stable and uniform overall gain. They badly wanted transistors with larger current gain so negative feedback could be employed. at the sacrifice of some circuit gain. to stabilize overall circuit performance against variations in operating conditions and transistor characteristics. Sid Darlington surely understood this engineering problem at the time. The following account of the origins of the Darlington transistor pair is due to Professor Emeritus Fiiscn Glanz at the University of New Hampshire. “Just after the transistor was invented at Bell Labs, Sid- ney checked out for the weekend two of the few existing transistors front the head of Bell Labs. Transistors Were not generally available and the head of the Labs kept the few that had been made in his desk. Sidney played with them at home on the weekend and discoveredjinvented the Darlington pair. He realized that they could be put in one package (“on one chip"), and that in fact any number of transistors could he put in one package. The next week he was encouraged to have the lawyers draw up the patent application. He said it should be Written for any number in one package, but the lawyers only Wanted to do it for twomwhich is what was applied for. As it turned out, if it had not been restricted to two transistors, Bell Labs and Dr. Darlington would receive Manuscript reamed May 1. l998. The author is with the Department of Electrical Engineering and Computer Sciences. University of Califomia at Berkeley. Berkeley. CA 947204776 USA. Publisher Item identifier S lOS?—7122(99)DDS45—0. R2 __ Fig. l. Burlington transistor pair. Resistors as shown are usually included to reduce the switching delay when turning off‘ a conducting pair. a royalty on every 1C chip made today! Anyway. that's the story he nails."l US. Patent 2663 806 titled "Semiconductor Signal Trans— lating Device" was issued on December 22, 1953 with Sidney Burlington as sole inventor. The drawings from the patent are reproduced here as an illustration on the following page. Drawings and claims are included for both two-transistor and three—transistor compound connections. (It seems that Sidney struck a compromise with the lawyers.) This patent often was cited as related art on patents issued subsequently. Ottline databases available today go back only to 1971; but from 197} to 1991, 17 subsequent patents reference this Darlington invention. Titles of these patents indicate uses ranging from power supplies to security apparatus to television receivers. Fig. 1 shows a Schematic diagram with transistors T1 and T2 connected as a Dariington transistor pair. The resistors shown are not essential, but are usually in cluded to permit independent design of bias currents and to reduce the time required to turn off a conducting pair. They reduce the current gain particularly at low currents. If we neglect the current flowing in the resistors and define the common-emitter current gain for a single consistor as ,8 = Ic/Ib, simple analysis shows that the overall dc or low frequency current gain for the Darlington pair is four/Ian = fir + 52 “i” 5152- 'See hopu’lwwweccatch.edult'acultylsidneylSDOrherhim], June 14. BBS. Quotation with Professor Glenn's permission. 10514122395105!) © 1999 EEEE 073/5, HODGES: DARLINGTON’S CDN’miEUTIONS m M5151 Dec. 22. 1953 Thus at low Frequencies the Burlington pair is approximately equivalent to a single transistor with a current gain greater than ,63. Electronic circuit designers welcemed the improvement in current gain. Unfortunately but not surprisingly. high frev an -n ....r ‘ SBAICONDUCTOR SIGNAL TRANSLATING DEVICE Filed May 9. 1.952 “13 2,653,806 inA/TOR 3‘ DAR]. (N6 TON ByflM ATTORNEY quency analysis shows that the Dm‘lingten pair has much more phase shift than a single transiston While a single transistor ampiifier stage usually is unconditionally stable when negative feedback is applied, this is not true of a single-stage amplifier ill-4 EEEE IRANSAC‘HONS ON CIRCUITS AND SYSTEMS—l: FUNDAMENTAL. THEORY AND APPLlCATiONS. VOL. 46. NO I. JANUARY 1999 using a Burlington pair. Conventional two-stage common— emitter transistor amplifiers are more easily rendered stable with negative feedback than single—stage amplifers using a Darlington pair. Therefore. the applications for Burlington pairs have been largely in noncritical circuits not requiring use of feedback. Another limitation is that the minimum voltage drop through the device when conducting must be greater than the base-emitter voltage (about 0.8 V) of the second transistor. When switching large currents. the powor wasted by this voltage drop can become an issue. The corrBSponding voltage drop for a simple summon-emitter transistor switch is about 0.2 V. The fact that the two transistors of a Darlington pair share a common collector region provokes the question of whether Sidney anticipated the development of the integrated circuit. Sidney's patent in fact diagrams and claims a transistor pair sharing a single n—type semiconductor region forming the common collector for a Dar‘lington pair. A jumper wire is shown making the connection between the emitter of one and the base of the other. At that time, the interconnecting jumper would have been applied by a manually controlled wire-bonding operation, one pair at a time. Modern planar integrated circuits readily provide hatch-interconnected bipolar transistors sharing a common collector region. One concludes that Sidney conceived some but not all of the essential Features of a modern integrated circuit, An Internet search for "Burlington transistor" shows that even to this day there are dozens of commercial devices so identified. typically featuring a current gain of [000 or more. They are used primarily for relay drivers and in other applications requiring simplicity and high gain. For example, they are widely used to actuate solenoid-driven flippers and flashing lights in electromechanical pinball machines. A,logic signal of a few milliamperes from a microprocessor. amplified by 21 Burlington transistor, easily switches an ampere or more at 56 V on a time scale measnreci in milliseconds. as required for actuating a solenoid or a tungsten lamp. Sidney Darlington made at least one other excursion into the world of transistor circuit design. According to Dr. Franklin Blecher. who joined Bell Laboratories around 1952, Sidney once desigied. built, and demonstrated a complete three-stage direct-coupled transistor amplifier of a sort that might be suitable for use in a hearing aid. This circuit used single o'ansistors, not Dariinglon pairs. Properly designed negative feedback. stabilizing the gain and dc operating point. was included? While this was an original undertaking for Sid, it turned out that others had demonstrated such circuits earlier. Sidney Darlington was a person of great curiosity and orig-v inality. armed with the best modern scientific and engineering lmowledge. The scope of his creative accomplishments is an inspiration to all who knew him. David A, Hodges (5'59—M'65~SM'7l-F‘77) rev ccived the 3.5.3.. degree from Cornell University, Ithaca. NY. and the MS. and PhD degrees from the University of California at Berkeley. From 1965 to £970 he worked at Bell Telephone Laboratories He was Professor of Electrics! En- gineering and Computer Science at University of California at Berkeley From 1970 to i998. He is now Professor in the Graduate School and Daniel M. Tciicp Distinguished Professor Emeritus He served as Dean oi Berkeley's College of Engineering item 1990 to 1996. He was active In teaching and msoarch on microelectronics technology and design Since l984 his research centered on semiconductor manufacturing systems He serves as a Director or Mentor Graphics Corpm ration. Silicon Image. inc. and the International Computer Science institute Prof. Hodges wns the founding editor of lite [BEE TMNSncTiDNS cm Sestlconoucroa MANUFACTURIND. a past editor of the IEEE JOURNAL on SOLID-STATE Cincurrs. and a past Chairman of the linematlonut Build-State Circuits Conference. He was the recipient of tltr: 1997 iEEE Education Medal. lie is a member at the National Academy of Engineering. :anklin H. Bicciter. private communication, April I. E998. 31/6 ...
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CH 6 Part 2 Multistage Amplifiers - 34/6 1&amp;quot;, u /...

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