Week 9: Multivibrators, MOSFET Amplifiers

Transcription

1 ELE 2110A Electronc Crcuts Week 9: Multbrators, MOSFET Aplfers Lecture 09-1

2 Multbrators Topcs to coer Snle-stae MOSFET aplfers Coon-source aplfer Coon-dran aplfer Coon-ate aplfer eadn Assnent: Chap of Jaeer and Blalock or Chap of Sedra & Sth Lecture 09-2

3 Multbrators A ultbrator s used to pleent sple two-state systes such as oscllators, ters and flp-flops. Three types: Astable nether state s stable. Applcatons: oscllator, etc. Monostable - one of the states s stable, but the other s not; Applcatons: ter, etc. Bstable t reans n ether state ndefntely. Applcatons: flp-flop, etc. eference: Lecture 09-3

4 Astable Multbrator edrawn Crcut n Experent A4 Conssts of two aplfyn deces cross-coupled by resstors and capactors. Typcally, 2 3, 1 4, C 1 C 2 and 2 >> 1. The crcut has two states State 1: V C1 LOW, V C1 HIGH, Q 1 ON (saturaton) and Q 2 OFF. State 2: V C1 HIGH, V C2 LOW, Q 1 OFF and Q 2 ON (saturaton). It contnuously oscllates fro one state to the other. Lecture 09-4

5 Basc Mode of Operatonal State 1: V B1 chares up throuh 3 fro below round towards V CC. When V B1 reaches V ON (of V BE, 1V), Q 1 turns on and pulls V C1 fro V CC to V CESat 0V. Due to forward-bas of the BE juncton of Q 1, V B1 reans at 1V. Lecture 09-5

6 Basc Mode of Operatonal 1V 1V-V CC V CC 0V V CC State 1 (cont d): As C 1 s oltae cannot chane nstantaneously, V B2 drops by V CC. Lecture 09-6

7 Basc Mode of Operatonal 0V 1V State 1 (cont d): Q 2 turns off and V C2 chares up throuh 4 to V CC (speed set by the te constant 4 C 2 ). V B2 chares up throuh 2 towards V CC (speed set by 2 C 1, whch s slower than the charn up speed of V C2 ). Lecture 09-7

8 Basc Mode of Operatonal 1V V CC 0V State 2: When V B2 reaches V ON, Q 2 turns on and pulls V C2 fro V CC to 0V. V B2 reans at V ON. Lecture 09-8

9 Basc Mode of Operatonal 1V 1V-V CC V CC 1V V CC 0V State 2 (cont d): As C 2 s oltae cannot chane nstantaneously, V B1 drops by V CC. Lecture 09-9

10 Basc Mode of Operatonal 1V 0V State 2 (cont d): Q 1 turns off and V C1 chares up throuh 1 to V CC, at a rate set by 1 C 1. V B2 chares up throuh 3 towards V CC, at a rate set by 3 C 2, whch s slower. Lecture 09-10

11 Basc Mode of Operatonal Back to state 1: When V B2 reaches Von, the crcut enters state 1 aan, and the process repeats. Lecture 09-11

12 Intal Power-Up When the crcut s frst powered up, nether transstor s ON. Parastc capactors between B and E of Q 1 and Q 2 are chared up towards V CC throuh 2 and 3. Both V B1 and V B2 rse. Inetable slht asyetres wll ean that one of the transstors s frst to swtch on. Ths wll quckly put the crcut nto one of the aboe states, and oscllaton wll ensue. Lecture 09-12

13 Multbrator Frequency t 0 0V T/2 B1 ( V V ON CC V CC + 2V ) + (2V CC (1 e CC V t / C 3 2 on ) )(1 e t / C for V 3 ON 2 ) << V CC At t T/2, B1 V ON : V ON V CC + T / 23C 2 2V (1 e CC ) Lecture 09-13

14 Multbrator Frequency V ON V CC + T / 23C2 2V (1 e ) CC V CC T / 23C2 2V (1 e ) CC for V << V ON CC / 23C2 1 2(1 e T ) e T / 2 C or T e T / 2 C T 2 C ln 2 2(ln 2) C f 1 2(ln 2) C 2 For the aboe coponent alues, f 1.53kHz. Lecture 09-14

15 Supply Voltae Lt V V ON CC When V B1 s neate, BE juncton of Q 1 s reerse-based. Suppose the breakdown oltae of ths juncton s V break (poste). then to aod breakdown, V V > V V < V + V ON CC Break CC ON Break Lecture 09-15

16 Mono-stable Multbrator Capacte path between V C2 and V B1 reoed. Stable for one state (state 1 here) Q 1 ON and Q 2 OFF V C1 LOW, V C1 HIGH When V B2 s oentarly pulled to round by an external snal V C2 rses to V CC Q 1 turns on V C1 pulled to 0V When the external snal oes hh V B2 chares up to V CC throuh 2 After a certan te T, V B2 V ON, Q 2 turns on V C2 pulled to 0V, Q 1 turns off Enters state 1 and reans there Can be used as a ter Lecture 09-16

17 B-stable Multbrator VCC Both capactors reoed Stable for ether state 1 or 2 Can be forced to ether state by Set or eset snals If Set s low, Q 1 turns off Vout Q1 V B1 V B2 Q2 Vout V C1 (V out ) and V B2 rses towards V CC Q 2 turns on V C2 (/V out ) pulled to 0V V B1 s latched to 0V Crcut reans n state 2 untl eset s low set reset If eset s low Slar operaton Crcut reans n state 1 untl Set s low Behae as an S flp-flop Lecture 09-17

18 Multbrators Topcs to coer Snle-stae MOSFET aplfers Coon-source aplfer Coon-dran aplfer Coon-ate aplfer Lecture 09-18

19 Coon-Source Aplfer Input Output Source Load AC round AC Equalent: Lecture 09-19

20 CS Aplfer Wth Source esstor Input Output Load Source AC round AC Equalent Also naed Source Deenerated Coon Source Aplfer Lecture 09-20

21 Coon-Dran Aplfer/Source Follower Input AC round Output Source Load G 1 2 AC equalent L 4 7 Lecture 09-21

22 Coon Gate Aplfer AC round Output Load L 3 7 Source AC equalent Input Lecture 09-22

23 Multbrators Topcs to coer Snle-stae MOSFET aplfers Coon-source aplfer Coon-dran aplfer Coon-ate aplfer Lecture 09-23

24 Coon-Source Aplfer nmos sall-snal odel AC Equalents L r o D 3 Lecture 09-24

25 Voltae Gan Ternal oltae an fro ate and dran s: A t d o s L Oerall oltae an fro source to o : A A o o s L s G + I G A t s Lecture 09-25

26 Input esstances n2 x x G n G Input resstance ( n2 ) lookn nto the ate ternal s nfnte. Input resstance ( n ) lookn nto the coupln capactor Lecture 09-26

27 Output esstance s 0. Output resstance lookn nto the output coupln capactor: out x x D r o D As r o >> D. Lecture 09-27

28 C-S Aplfer Wth Source esstor AC Equalents Lecture 09-28

29 Lecture Ternal Voltae Gan Ternal oltae an: Voltae an s less senste to after addn S. S L o CS t L d o S d S d d S d s s d A ) ( Note: body effect and r o hae been nored.

30 Lecture Input Snal ane ) 0.2( 1 TN V GS V S s + ) )(1 0.2( S TN V GS V + Input snal rane: antude of s ust be less than 0.2(V GS - V TN ) Presence of S ncreases nput rane. S s S S S d s S d Q

31 n and Oerall oltae an Input resstance lookn nto the ate ternal: CS n Oerall oltae an: A CS A CS t G + I G Lecture 09-31

32 Lecture Output esstance + S r o CS out 1 Output resstance: ) (1 ) ( )] ( [ S o S o o S d d S d d o S d d s d o s d S d s r r r r r for S << r o Include r o n the odel S + s - s r o d d

33 Suary of Coon Source Aplfer Lare and Inertn oltae an Infnte nput resstance lookn nto the Gate ternal Lare output resstance Input snal oltae rane depends on source resstance Sutable for nternal oltae an stae Need a oltae buffer to dre low load resstance. Lecture 09-33

34 Topcs to coer MOSFET crcuts DC analyss Buldn sall snal odel for MOSFET Snle-stae MOSFET aplfers Coon-source aplfer Coon-dran aplfer Coon-ate aplfer Lecture 09-34

35 CD Aplfer / Source Follower AC equalent: G 1 2 L 4 7 nmos sall-snal odel Lecture 09-35

36 Sall Snal Analyss Input resstance lookn nto Gate: ( ) o Ternal oltae an: A CD o L t + 1+ L o For ost cases, L >>1, ternal oltae an s close to 1. Hence the nae source follower. L A CD CD n Oerall oltae an: s A CD t G + I G Input snal rane: 0.2( V V ) 1+ GS TN L 0.2( V V )(1+ GS TN L ) Lecture 09-36

37 Output esstance (nore the r o ) x Output resstance: ( ) x s x x out x x 1 Note: n the analyss for CD aplfer the body effect has be nored. More accurate analyss should nclude the body effect. Lecture 09-37

38 Suary of Source Follower Unty oltae an Infnte nput resstance (excludn the bas resstors) Low output resstance (1/G) Lare nput snal oltae rane Sutable for oltae buffer Lecture 09-38

39 Topcs to coer MOSFET crcuts DC analyss Buldn sall snal odel for MOSFET Snle-stae MOSFET aplfers Coon-source aplfer Coon-dran aplfer Coon-ate aplfer Lecture 09-39

40 Coon Gate Aplfer L 3 7 AC equalent nmos sall-snal odel Lecture 09-40

41 Lecture Sall Snal Analyss CG n 1 Ternal oltae an: Input resstance lookn nto Source: Oerall oltae an: (sae as the out of CD) L A CG t + The an s non-nertn I L A CG ) 4 ( I I L CG n I CG n A CG t o o A CG For I >> 4, ) L ( s L s o

42 Input Snal ane Input snal rane: s I I + 4 1/ + 1/ 1 1+ (1/ (1/ 4 I ) ) for 1/ >> 4 0.2( V V )(1+ GS TN I elate sze of and I deterne snal-handln lts. ) Lecture 09-42

43 Output esstance Output resstance: x s ( ) x th x 0 and thus out th I 4 Includn the r o n the transstor, x ( s ( s ) + ( x + 1/ r o s ) + ) / r x o / r o s out th r o x x x r o ( 1+ ( + 1/ r )) ( 1+ ) th th o Lecture 09-43

44 Current Gans Ternal current an: Snce I D I S, the ternal current s unty. Oerall current an: A I 4 + 1/ 4 1 Lecture 09-44

45 Suary of Coon Gate Aplfer Unty Current Gan Lare Non-nertn oltae an Low nput resstance (1/G) Lare output resstance Input oltae rane depends on I Sutable for current buffer Lecture 09-45