common source amplifier: the source is connected with the ground from the point of view of ac small signal equivalent circuits,

Transcription

1 cvy: evse all abo he jncon eld eec ranssors (j-fets and eal-oxdsecondcor eld eec ranssors (MO-FETs, her devce odels, he paraeers o he devce odels, her calclaon and se he bas po o he eld eec ranssors. Conens:.. syercal aplers wh eld eec ranssors n hs chaper we can d he analyses o he asyercal aplers bl ro n-channel jncon eld eec ranssors (j-fets. Or conseqences are sable o be sed case o any ypes o FETs. Thereore or saeens are sable or MO-FETs aplers, oo. lke he crcs bl ro bpolar ranssors he prevos chaper, here are hree basc ypes o he asyercal aplers cona FET-s depend on whch eral o he eld eec ranssor connecs wh he rond he sall sal eqvalen crc o he apler. The hree ypes o he base FETs aplers are as ollows: coon sorce apler: he sorce s conneced wh he rond ro he po o vew o ac sall sal eqvalen crcs, he p sal oes o he ae o he eld eec ranssor, he op sal coes ro he dra. coon dra apler: he dra s conneced wh he rond ro he po o vew o ac sall sal eqvalen crcs, he p sal oes o he ae o he eld eec ranssor, he op sal coes ro he sorce. coon ae apler: he ae s conneced wh he rond ro he po o vew o ac sall sal eqvalen crcs, he p sal oes o he sorce o he eld eec ranssor, he op sal coes ro he dra.

2 .. Coon sorce apler (wh sorce capacor parallel wh he sorce ressor pply n-channel jncon eld eec ranssor as an acve devce or he apler and posve sppler volae, he ollow apler can be assebled. The res below show he apler and s eqvalen crc o he coon sorce apler: Coon sorce apler (wh sorce capacor C s parallel wh he sorce ressor s The ac sall sal eqvalen crc o he coon sorce apler (he sorce eral s conneced drecly wh he rond Based on he eqvalen crc, he work paraeers can be calclaed he ollow way. Le s sar wh he volae aplcaon rae o he apler : o G G

3 The orla above can be spled, becase he vale o he / s ch hher han he vale o or. Frherore, s eqal o The vale o he p ressance corresponds o he vale o he ae ressance G, becase case o FETs he ressance beween he ae and sorce erals s praccally e hh. (The vale o he ressance beween hese wo erals s oen 0 or order o. G The op ressance o he crc s ven wh he orla below: o The crren aplcaon rae o he coon sorce apler can be deed he ollow way: o G G G G ppos, he orla above can be spled lke hs: G..B Coon sorce apler (wh sorce ressance and who sorce capacor The coon sorce apler (who sorce capacor and s eqvalen crc can be seen he res below:

4 The coon sorce apler who sorce capacor The eqvalen crc o he coon sorce apler where he sorce capacor s ss n hs apler he sorce ressance s ors a neave crren eedback he crc. Thereore, he work paraeers o he prevos apler can chane scanly. (r he calclaons he eqaly s spposed. The vale o he volae aplcaon rae decreases as can be ven he orla below: o G G G The vale o he p ressance reas nchaned. s vale s also G. G

5 The vale o he op ressance also reas praccally. Thoh he vale o he s creased by he eedback, he eec o he eedback hs case can be neleced: o The vale o he crren aplcaon rae o he crc s as ollows: G G..C Coon dra apler The assebly and he eqvalen crc o he coon dra apler can be seen he res below: Coon dra apler Eqvalen crc o he coon dra apler

6 s he eqvalen crc, he volae aplcaon rae o he coon dra apler has he ollow orla: o G G G ( ( where nornaely, case o eld eec ranssors he vale o her ranscondcance s saller han ha vale case o bpolar ranssors. Thereore, he vale o he prodc s oen lower han 0. o he volae aplcaon rae o he coon dra apler s expeced o be as low as abo The vale o he p ressance o hs crc s also eqal o he vale o he ae ressance G : G r he calclaon o he op ressance, he eec o he conrolled crren eneraor s be aken o consderaon. The volae level on s as lare as he p volae level G, eanwhle he crren rnn hroh s G. Thereore he ressance o he eneraor s eqal o /. o The vale o he op ressance s abo 00, he vale o he p ressance can be several M a he sae e. The vale o he volae aplcaon rae s nearly a n. Becase o all hese eares o he coon dra apler hs crc s nearly an deal volae ollower. The crren aplcaon rae o he coon dra apler can be ven wh he orla below: G..C Coon ae apler

7 ssebly o he coon ae apler Eqvalen crc o he coon ae apler s he eqvalen crc, he work paraeers o he coon ae apler are as ollows: o G ( ( G (n he calclaon s also spposed. The vale o he p ressance o he coon ae apler can be deed wh he orla below:

8 The crren o he conrolled p eneraor, ha s consderaon. ce he p volae s eqal o conneced parallel wh he sorce ressance s. G, s also be aken o G, a ressor wh a vale o The vale o he op ressance o he coon ae apler s praccally eqal o he vale o he dra ressance o The crren aplcaon rae o he coon ae apler s deed by he crren dvder beween and. s cvy: Thk over and repea he work paraeers and her vales o he aplers lsed above. Place hese crcs order accord o her volae aplcaon rae, p and op ressance and crren aplcaon rae. Look or ypcal applcaons or all aplers where her benecal eares can be lzed he bes. EXMPLE:.. e p he volae level o he dra o 5 V by vary he vale o he ollow crc. Then dee all oher paraeers o he bas he apler. Fally, calclae he work paraeers o he apler, oo. aa: 0 = 4 V; 0 = ; = 4, = 0

9 The vale o he ae crren s nelbly sall; s vale s abo 0 -. Thereore he vale o he ae volae G ses exacly hal-way o he volae level o he power spply: M 4 V V G M M The sorce volae depends on he dra crren as ollows: The derence beween hese wo vales ves he volae level G : G G V V k The ollow relaon can be descrbed beween he ae-sorce volae and he dra crren he bas o he eld eec ranssor s he saraon reon (hs asspon s be checked laer know he bas o he crc: 0 G G 4 0 V bse he relaon above abo he ae-sorce volae V k 4V Ths relaon s a sple and qadrac eqaon or : o hs eqaon: G ( ( per Ths eqaon has o wo roos: 5.3 and 3

10 One o he wo roos s alse. Calclae he level o he ae-sorce boh cases o decde whch one o he s re:.3v and 6V G G n case o he rs solon G < 0, hereore he dra crren s eqal o zero hs e, becase he eld eec ranssor s sll closed. The second resl ves he rh solon, where he ae-sorce volae s 6 V. n hs case he vale o he dra crren s 3 and he volae level o he sorce s V 6 V = 6 V. The dra volae s known o be se p 5 V. pply 4 V as a volae level o he power spply, he volae level all on he dra ressance s as ollows: 4V 5V 9V The vale o he dra ressance wh he crren level calclaed above s 3 kω: 9V 3k 3 s hh e o check wheher he bas o he eld eec ranssor works he saraon or he lear reon. Calclaons s be done o know he vales o he nex eqaly: ha s G 0 5V 6V 9V V 6V 4V The bas po o he eld eec ranssor has allen he saraon reon. o he sar asspon and he procedre o he whole calclaon are rh. The ac sall sal eqvalen crc o he apler above s as ollows: G 0 To calclae he seres o he work paraeers, sar o deere he vale o he volae aplcaon rae o he apler: 4.87 k.5 (.db 3k 68 k. 87 k The vale o he p ressance can be deered wh he parallel ressances - o he ae dvder: M M 500 k The op ressance s praccally eqal o he dra ressance :

11 3k o The vale o he crren ressance ors accord o he ollow relaon: 3k k 84.5 (38.5dB 3k 68 k ( The eneral eqaon or he crren aplcaon rae ves he sae resl: 500 k ( (38.5dB 68 k Fally, he vale o he power aplcaon rae can be seen he ollow le: p (9.9dB..B e p he dra-sorce volae level o 7 V by vary he vale o he ollow crc. Calclae he work paraeers o he apler, oo. aa: 0 = -6 V; 0 = 8 ; = 3, = 0 Le s see he ollow eqaon: 0 n he eqaon above only wo paraeers are known: he vales o 0 and 0. Le s reard he vale o as a varable paraeer. n hs case: G 0 G 0 G and bse he real vale o he known paraeers he las eqaon and express he sorce ressance as a ncon o he dra crren :

12 0 V 7V 5k 3 V ( 5k 3V 5k Ths relaon s be sbsed he second eqaon: 3V 5k 5k 3V G o besde he rs eqaon, he le above resls a new relaon beween he dra crren and he ae-sorce volae level G. We have o wo nknown paraeers and wo eqaons or he. s hese wo eqaons, a sple qadrac eqaon can be ored or he dra crren : 5k 3V 8 6V Express he eqaon above, he nex relaon can be receved: There are wo solons o hs qadrac eqaon as sal: ( and eere he ae-sorce volaes belon o each roo boh cases based on he relaon 5k V : 3 G 3V and 8. V G G s can be seen G < 0, s easy o check ha hs resl s alse. Thereore he vale o he dra crren s eqal o and -3 V s he rh solon or he ae-sorce volae. Know he dra crren, he volae levels o he dra and he sorce are as ollows: 0V 5k 0V 3V The derence beween hese wo volae levels s really 7 V as was speced a he ben o he exaple. The bas o he eld eec ranssor has acally allen he saraon reon as well: 0V 3V 7V 3V 3V 6V G 0

13 er deer he bas o he crc and he vale o he sorce ressance, he work paraeers are he nex o be calclaed: ( 3 (5k 33 k 3.5k.37 (7.5dB M G ( 5k o M ( (37 db 33 k p 70 (.3dB r he calclaon he vale o / s spposed o be larer han he vale o he dra ressance...c e p he sorce volae level o be hal-way o he volae o he power spply by vary he vale o he ollow crc. Calclae he work paraeers o he apler, oo. aa: 0 =.5 V; 0 = 5 ; =.4, = 8

14 ce he vale o he ae crren s very sall, can be neleced, he volae level o he ae eral s eqal o he rond poenal G 0V. The vale o he sorce volae level s be se p hal-way o he volae level o he power spply. n hs case /. 75V. Fro hese wo daa he ae-sorce volae can be calclaed lke hs: 0V (.75V. 75V G G ppos he bas o he eld eec ranssor alls he saraon reon, he dra crren can be calclaed based on he qadrac relaon beween he dra crren and he aesorce volae G : G V 5.5V 450 Know he dra crren a he bas po, he vale o he sorce ressance can be ven he ollow way: 0.75V Beore o on, yo s ake sre wheher he bas o he eld eec ranssor s he saraon reon. Ths asspon eans ha he ollow eqaly s be rh case o a p-channel jncon eld eec ranssor: k er sbs: G 0.75V 0.75V Ths eans ha he asspon s rh and he calclaon above s sable. The eqvalen crc o he apler below can help o calclae he work paraeers o he crc: G 0 Wh he calclaon based on he eqvalen crc, s easy o dee he work paraeers: k k 0.89 ( db

15 3.8 k 47 k 3.8 k 5 k 47 k k k G o o o 3.8 k 3.8 k 5 k k (.db 47 k p.45 (0.6dB.. e p he dra volae level o V by vary he vale o he sorce ressance he ollow crc. Then dee all oher paraeers o he bas he apler. Calclae he work paraeers o he apler, oo. aa: 0 = V; 0 = 4 ; = 3.8, = 0 The vale o he dra crren a he bas po s deed clearly by he spply volae, he dra volae level and he vale o he dra ressance: 0V V 8V k 3.5 k Know he vale o he dra crren, he ae-sorce volae level can be calclaed wh he help o he ollow qadrac relaon: 0 G 0

16 G.56 4 V 0.8 There are wo solons or he ae-sorce volae: G V 0.4V and 3. 6V G G The rs roo can no be he rh solon o he exaple, becase hs vale s saller han he vale o he hreshold volae o he MO-FET. nder hs hreshold volae he MO- FET s closed, here s no any crren rnn hroh s erals. However he second roo alls he possble reon o he ae-sorce volae rane, sce 0 G o he rh solon s 3.6 V. The vale o he ae volae s exacly he hal o he volae level o he power spply becase o he nloaded ressor dvder - : G 0V er he vale o he sorce volae can also be ven: 0V 3.6V 6. 4V G G Based on he Oh s law he vale o he sorce ressance s be choosen.5 kω: 6.4V. 5k.56 ce he asspon s rh, he MO-FET s work he saraon reon: 5.6V 3.6V V G 0 The exaple shows a coon ae apler, he eqvalen crc o whch can be seen below: s hs eqvalen crc, he work paraeers can be calclaed he ollow way: ( k 0.8 (0.7 db

17 3.5 k 33 k. 85 k r he calclaon above he vale o he dra ressance s spposed o be ch larer han he vale o he paraeer..5k.5k o k (.db 33 k Fally, he vale o he power aplcaon rae can be ven lke hs: p ( 0.75 db Exercses or slaons:.a. sseble he ollow crc on PCE cheacs. se a ss wave eneraor (VN as an p sal, he aplde o whch s 00 V and s reqency s khz: lae he vales o he ollow paraeers he apler: G,, G and.