Bipolar Junction Transistor (BJT)

Transcription

1 polar Juncton Transstor (JT) Lecture notes: Sec. 3 Sedra & Smth (6 th Ed): Sec * Sedra & Smth (5 th Ed): Sec * * Includes detals of JT dece operaton whch s not coered n ths course F. Najmabad, EE65, Wnter 212

2 A JT conssts of three regons NPN transstor Smplfed physcal structure An mplementaton on an I ece s constructed such that JT does NOT act as two dodes back to back (when oltages are appled to all three termnals). ece constructon s NOT symmetrc o Thn base regon (between E & ) o Healy doped emtter o Large area collector F. Najmabad, EE65, Wnter 212

3 JT characterstcs ncludes four parameters NPN transstor Sx crcut arables: (3 and 3 ) Two can be wrtten n terms of the other four: KL : KL : E + E E rcut symbol and onenton for current drectons (Note: E E ) JT characterstcs s the relatonshp among (,, E, and E ) It s typcally dered as f ( E ) g (, ) E F. Najmabad, EE65, Wnter 212

4 JT operaton n the acte mode E juncton s forward based ( E ) As Emtter s healy doped, a large number of electrons dffuse nto the base (only a small fracton combne wth holes) The number of these electrons scales as e E / T If the base s thn these electrons get near the depleton regon of juncton and are swept nto the collector f ( : juncton s reerse based!) I S e E / T E Acte mode: I S e I S e E F. Najmabad, EE65, Wnter 212 / T E / T In ths pcture, c s ndependent of (and E ) as long as E E E E ase current s also proportonal to e E / T and therefore, : /

5 JT operaton n saturaton mode E juncton s forward based ( E ) Smlar to the acte mode, a large number of electrons dffuse nto the base. For juncton s forward based and a dffuson current wll set up, reducng. 1. Soft saturaton: E.3 (S)*.4 (S), dffuson current s small and s ery close to ts acte-mode leel. F. Najmabad, EE65, Wnter 212 eep Saturaton mode: I S E / T e E < sat 2. eep saturaton regon:.1 < E <.3 (S) or E.2 sat (S), s smaller than ts acte-mode leel ( < ). o alled saturaton as s set by outsde crcut & does not respond to changes n. 3. Near cut-off: E.1 (S) oth & are close to zero. * Sedra & Smth ncludes ths n the acte regon,.e., JT s n acte mode as long as E.3.

6 JT characterstcs ncludes four parameters NPN transstor Smplfed physcal structure rcut symbol and onenton for current drectons (Note: E E ) JT characterstcs s the relatonshp among (,, E, and E ) It s typcally dered as f ( ) g ( E, E ) F. Najmabad, EE65, Wnter 212

7 JT characterstcs: f( E ) & g(, E ) Saturaton: E s forward based, s forward based 1. Soft saturaton: 2. eep saturaton: 3. Near cut-off:.3.7, E.1.3, < E E.1, Acte: E s forward based s reerse based F. Najmabad, EE65, Wnter 212 ut-off : E s reerse based,

8 Early Effect modfes characterstcs n the acte mode s NOT constant n the acte regon. Early Effect: Lnes of s E for dfferent (or E ) concde at E A I e + / T E S A E 1 F. Najmabad, EE65, Wnter 212

9 NPN JT equatons Lnear model ut-off : E s reerse based, E, < Acte: E s forward based s reerse based I S e E I S e / T E / T 1 + E A E,, E (eep) Saturaton: E s forward based s reerse based E I S e sat E, / T < E E sat,, < For S,.7, sat.2 F. Najmabad, EE65, Wnter 212

10 PNP transstor s the analog to NPN JT PNP transstor Lnear model ut-off : E s reerse based E, < Acte: E s forward based s reerse based E,, E ompared to a NPN: 1) urrent drectons are reersed 2) oltage subscrpts swtched (eep) Saturaton: E s forward based s reerse based E E,, sat < F. Najmabad, EE65, Wnter 212

11 Notatons esstors: Use subscrpt of JT termnal:,, E. oltages: Use ouble subscrpt of JT termnal:,, EE. oltage sources are dentfed by node oltage! F. Najmabad, EE65, Wnter 212

12 Transstor operates lke a ale: & E are controlled by ontroller part: rcut connected to E sets ontrolled part: & E are set by transstor state (& outsde crcut) ut-off ( ): ale losed Acte ( > ): ale partally open Saturaton ( > ): ale open < lmted by crcut connected to E termnals, ncreasng does not ncrease F. Najmabad, EE65, Wnter 212

13 ecpe for solng JT crcuts (State of JT s unknown before solng the crcut) 1. Wrte down E-KL and E-KL: 2. Assume JT s OFF, Use E-KL to check: a. JT OFF: Set, use E-KL to fnd E (one!) b. JT ON: ompute 3. Assume JT n acte. Set. Use E-KL to fnd E. If E, Assumpton orrect, otherwse n saturaton: 4. JT n Saturaton. Set E sat. Use E-KL to fnd. (ouble-check < ) NOTE: o For crcuts wth E, both E-KL & E-KL hae to be soled smultaneously. F. Najmabad, EE65, Wnter 212

14 Example 1: ompute transstor parameters (S JT wth 1). E - KL : E - KL : E E Assume ut - off : and 3 E - KL : E 4 > E E < E Assumpton ncorrect E ON : E - KL : E and µ A > Assume Acte: E - KL : E > 3 6 and ma 3 E + E.7 E.7 Assumpton correct 3.75 F. Najmabad, EE65, Wnter 212

15 JT Transfer Functon (1) E - KL : E - KL : + E + E ut - off : and E < E - KL : + E - KL : E + E For < JT n utoff,, E E E F. Najmabad, EE65, Wnter 212 E ON : E - KL : E and +

16 JT Transfer Functon (2) F. Najmabad, EE65, Wnter 212 E E + E - KL : and ON : E E E E E c - / E - KL : and Acte: + + JT n acte / For +

17 JT Transfer Functon (3) E ON : E and E - KL : + E Saturaaton : E - KL : c < E > IH sat + and sat c < + / sat - sat For / + < JT n saturaton F. Najmabad, EE65, Wnter 212

18 JT Transfer Functon (4) F. Najmabad, EE65, Wnter 212 JT n deep saturaton / JT n acte / JT n utoff < + + < sat

19 JT transfer functon on the load lne Saturaton : < IH ncreases but unchanged Load Lne (E - KL) E Acte: IH & ncrease together ut off < : F. Najmabad, EE65, Wnter 212

20 JT as a swtch Load s placed n collector crcut Use: Logc gate can turn loads ON (JT n saturaton) or OFF (JT n cut-off) c s unquely set by E crcut (as ce sat ) s chosen such that JT s n deep saturaton wth a wde margn (e.g.,.2 c /) F. Najmabad, EE65, Wnter 212 *Lab 4 crcut Soled n Lecture notes (problems 12 & 13)

21 JT as a gtal Gate esstor-transstor logc (TL) TL NOT gate ( L sat, H ) TL NO gate* TL NAN gate* Other arants: ode-transstor logc (TL) and transstor-transstor logc (TTL) JT logc gates are not used anymore except for hgh-speed emtter-coupled logc crcuts o Low speed (swtchng to saturaton s qute slow). o Large space and power requrements on Is F. Najmabad, EE65, Wnter 212 *Soled n Lecture notes (problems 14 & 15)

22 JT ares substantally Our JT model ncludes three parameters:, sat and o and sat depend on base semconductor: o For S,.7, sat.2 Transstor depends on many factors: o Strongly depends on temperature (9% ncrease per o ) o epends on (not constant as assumed n the model) o of smlarly manufactured JT can ary (manufacturer spec sheet typcally ges a range as well as an aerage alue for ) o We wll use the aerage n calculatons (PSpce also uses aerage but ncludes temperature and dependence). o mn s an mportant parameter. For example, to ensure operaton n deep saturaton for all smlar model JTs, we need to set / < mn F. Najmabad, EE65, Wnter 212