Common Source Common Source Small Signal

Transcription

1 MOSET Confguratons Common source Common Dra Source follower Common gate MOSET Confguratons Op mps, 5 Imperfectons Op amp applcatons cknowledgements: on oscoe, Neamen, Donald: Mcroelectroncs Crcut nalyss and Desgn, rd Edton.0 Sprg 0 Lecture.0 Sprg 0 Lecture Common Source Common Source Small Sgnal o g m ( r D ) o.0 Sprg 0 Lecture.0 Sprg 0 Lecture

2 Common Dra Source ollower Common Dra Source ollower Output Impedance ( S o S ro S m g r ) O g m S r o.0 Sprg 0 Lecture 5.0 Sprg 0 Lecture Common Gate Common Gate Small Sgnal g m ( D L ) g ms I I O D ( D L g ms )( g m S ).0 Sprg 0 Lecture.0 Sprg 0 Lecture 8

3 MOSET Confguraton Summary Confguraton oltage Ga Common Source > Source ollower Current Ga Input esstance TH TH Common Gate > Low Output esstance Moderate to hgh Low Moderate to hgh JET pplcaton Current Source Household applcaton: battery charger (car, laptop, mp players) Dfferental amplfer current source amp waeform generator Hgh Speed D conerter usg capactors Smple crcut: N559 Nchannel JET I DSS = current wth GS =0 P = pchoff oltage D I DSS GS P 5 N559 D.0 Sprg 0 Lecture 9.0 Sprg 0 0 Op mps Op mp Packagg cte dece: 0 = a( ); note that t s the dfference of the put oltage! a=open loop ga ~ Most applcatons use negate feedback. Comparator: no feedback o cte dece requres power. No shown for smplcty. Classcs opamps:, 5 ~ $0.0; one, two or four a package. L5 LM.0 Sprg 0 Lecture.0 Sprg 0

4 5 JET Input Op amp JET Dfferental Par Small Sgnal Model.0 Sprg 0 Lecture.0 Sprg 0 Crcut Dfferental (Emtter Coupled) Par JT Dff Par Small Sgnal Model transstors, resstors, capactor, dode.0 Sprg 0 Lecture 5.0 Sprg 0

5 Dfferental Par Common Mode oltage Dfferental Par Dfferental Mode oltage Small Sgnal Model.0 Sprg 0.0 Sprg 0 8 MOSET Dfferental Par rtual Node nalyss Small Sgnal Model = a( ) a = ga β = feedback or loop functon a If a>> and a>> β then ~ Current to put termals zero by desgn x x x a a a a x a x a a Typcal alues: a~00,000 & a β >> ok for a=a(s) and β = β(s) as long as a(s) β(s) >> β s the loop transfer functon (not to be confused of β of a JT) aβ s the loop ga.0 Sprg Sprg 0 0 Lecture

6 Op mps rtual Node Wth negate feedback, put wll dre the put oltage dfference to zero => = Input current = 0 enefts of eedback Stablze ga agast dece aratons, temperature, agg Input and put mpedances adjusted by (aβ) educe dstorton by the feedback factor [(aβ)] Ga determed by passe components Op mp Max atgs common mode oltage appears at both puts Need cc, ee for operaton Dsadantages of eedback Loss of ga; need more stages Greater tendency for stablty (oscllatons) Idot proof a x a a.0 Sprg 0 Lecture.0 Sprg 0 Lecture Electrcal Characterstcs L5 lmost zero not ral to ral.0 Sprg 0 Lecture.0 Sprg 0 Lecture

7 LM5 al to al Output Decbel (d) d 0log o Po d 0log P log 0 ()=.0 00 d = 00,000 = d = 0,000 = 0 d pot = half power pot 0 d =,000 = 0 0 d = 00 = 0.0 Sprg 0 Lecture 5.0 Sprg 0 Lecture Open Loop requency Ga.0 Sprg 0 Lecture s Non Inertg mplfer 5 5 β (not to be confused wth β of a JT) for fte Zero put current; therefore so.0 Sprg 0 8 or but ;

8 5 s 5 Open Loop requency Ga Examples at Hz, 000 Hz, and 0kHz oltage ga =0d = 00; = 00k, = k; [0 = 0.d!] β=0.0 t Hz, ol = 00 d = x 0 5 = 00, d t 000 Hz, ol = 0 d = 0 = d t 0 khz, ol = d =. x 0 = d.0.. β s the loop transfer functon aβ s the loop ga.0 Sprg 0 Lecture 9 s 5 Comparson 5 Input dece JT JET Input bas current 0.5u 0.000u Input resstance 0. MΩ 0 MΩ Slew rate* 0.5 /us.5 /us Ga andwdth product Mhz 5 Mhz Output short crcut duraton contuous contuous Identcal p * comparators hae >50 /us slew rate.0 Sprg 0 Lecture 0 So Why JT Op amps? Ga andwdth Product = Constant (No free lunch) JTs hae hgher transconductance (ga), better consstency spec between peces, and some applcatons, lower nose than ETs. Lke most JET op amps, the L5 has a relately hgh offset oltage, and relately hgh drfts. JT opamps tend to hae much lower offset oltage and drfts. Ga: 0d = 0 andwdth = 5x0 Ga andwdth product = 5x0.0 Sprg 0.0 Sprg 0 Lecture

9 Op mp Imperfectons eal World Input Offset oltage * Input offset oltage Input Current as Input Offset Current te Output oltage Swg te Current te Ga, ga bandwdth product oltage Nose Johnson Nose Phase Shfts Slew ate * nalog Deces MT0 Tutoral.0 Sprg 0 Lecture.0 Sprg 0 Lecture Offset djustments Input as Current * The put offset current, I OS, s the dfference between I and I, or I OS = I I. * nalog Deces MT08 Tutoral.0 Sprg 0 Lecture 5.0 Sprg 0 Lecture

10 Inertg mplfer Offset Current Compensaton I I 5 I 5 O // I I DI OUT OL but wth no put I thus : 5 I 5 OUT O I O sgnal, I O I ; as OUT OUT I I 0 f 0 and we want O I a condton I // OUT I // I // OUT 0 I OUT 0, so : for no offset at I OL OL o Common Mode ejecton ato CM CM: rato of the commonmode ga to dfferentalmode ga. Example, f a dfferental put change of Y olts produces a change of at the put, and a commonmode change of X olts produces a smlar change of, then the CM s X/Y. CM often expressed d: CM 0log OL CM OUT 0 f //.0 Sprg 0 Lecture.0 Sprg 0 Lecture 8 Inertg mplfer rtual Ground nalyss ssumptons Infte put mpedance: 0; 0 0 because s grounded. f Schmtt Trgger o Schmtt trgger hae dfferent trggers pots for rsg edge and fallg edge. f 5 5 f f f f 0 Can be used to reduce false trggerg Ths s NOT a negate feedback crcut..0 Sprg 0 Lecture 9.0 Sprg 0 Lecture 0

11 Schmtt Trgger C eedback = Oscllator Hgh Pass lter HP (d) 0K op amp. =0k, =.k, =0K, C=.uf C 0 d slope = d / octae slope = 0 d / decade 0.uf 0K Dsplay and on the scope. Set =.k. Predct what happens to the frequency. j C s C j C s C j C 90 o Degrees f LO or f d PHSE LED 5 o 0 o.k 5 o f LO or f d.0 Sprg 0 Lecture.0 Sprg 0 Lecture Dfferentator Insghts Low Pass lter LP (d) (d) 0 d slope = d / octae slope = 0 d / decade C 0 d slope = d / octae slope = 0 d / decade sc sc ; sc s j ; at low frequency sc sc Degrees 90 o 5 o 0 o 5 o f LO or f d f LO or f d PHSE LED sc j X C j X C j C j C j C 0 o 5 o 90 o Degrees PHSE LG f HI or f d f HI or f d multplyg by s equals dfferentaton tegraton works only at f 0 x f sc HI.0 Sprg 0 Lecture.0 Sprg 0 Lecture

12 Integrator Insghts (d) Why? 0 d Degrees slope = d / octae slope = 0 d / decade f HI or f d Wth, any DC bas current wll saturate sce the DC ga s the open loop ga 0 o PHSE LG ; sc at hgh frequency s j; sc 5 o 90 o f HI or f d sc sc tegraton works only at f 0 x f HI sc ddg by s equals tegraton.0 Sprg 0 Lecture 5.0 Sprg 0 Lecture Integraton and dfferentaton easy to understand tme doma requency Doma Insght In frequency doma, dfference between square wae and trangle wae s ampltude and phase same harmoncs. Integrator (LP) rolls off harmoncs and phase shft to create a trangle wae Dfferentator (HP) amplfes harmoncs and phase shft to create a square wae. oltage ollower (buffer) Dfferental Input asc Opmp Crcuts Nonertg Integrator C.0 Sprg 0 Lecture C t dt 8

13 Crossoer Dstorton (hole) Dode asg 0k 0k 0k 0. L5 0.?k [a] 5 5 N90 5 0k N90 L 5 L5?k [b] N N L C [rom Preamplfer]?opamp D 9 D N9 N9 E =5. / watt E =5. / watt N905 N00 N00 L Why s [b] better? Lecture.0 Sprg 0 9 Lecture.0 Sprg 0 50