ELCT 503: Semiconductors. Fall 2014

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1 EL503 Semconductors Fall 2014 Lecture 09: BJ rcut Analyss Dr. Hassan Mostafa د. حسن مصطفى EL 503: Semconductors

2 ntroducton npn transstor pnp transstor EL 503: Semconductors

3 ntroducton Symbol EL 503: Semconductors

4 D Models npn BEJ BJ EL 503: Semconductors

5 D Models B characterstcs for common-base confguraton EL 503: Semconductors

6 D Models E characterstcs for common-emtter confguraton ( A = Early oltage) EL 503: Semconductors

7 D Models (npn) ransstor OFF ( BE < 0.7) and ( B < 0.4) B = 0 = 0 E = 0 ransstor n Acte regon ( BE >= 0.7) and ( B < 0.4) E >=0.3 = S exp ( BE / ) = β B E = + B = (β+1) B = E β = / (1- ) and β >> 1 = β / (β+1) and <= 1 EL 503: Semconductors

8 D Models (npn) ransstor n Saturaton regon ( BE >= 0.7) and ( B >= 0.4) E =0.2 sat = β forced B E = + B = (β forced +1) B EL 503: Semconductors

9 D Models (pnp) Same equatons as before but after changng letters order: BE EB B B E E EL 503: Semconductors

10 Example1 β = 100 BE = 0.7 at = 1 ma Desgn the crcut such that: = 2 ma = +5 EL 503: Semconductors

11 Example1 Soluton 15 5 R 5k 2mA ransstor works n the acte regon BE B 0.7 B EL 503: Semconductors

12 Example1 Soluton E R BE BE E E mA 0.7 *ln( ) mA E / *2mA 100 ( 15) 7.07k E B E E 2.02mA EL 503: Semconductors

13 Example2 β = 100 Fnd, B, E, B,, and E Assume Acte regon BE = 0.7 EL 503: Semconductors

14 Example2 heck: ( BE >= 0.7) ( B = -1.3 < 0.4) orrect EL 503: Semconductors

15 Example3 β = 100 Fnd, B, E, B,, and E Assume Acte regon heck: ( BE >= 0.7) ( B = 3.52 > 0.4) ncorrect EL 503: Semconductors

16 Example3 Assume Saturaton regon heck: ( BE >= 0.7) ( B = 0.5 > 0.4) orrect EL 503: Semconductors

17 BJ n Logc Gates RL (Resstor ransstor Logc) o o When When E S E BE BE *exp( ncreasng BE decrease o BE Assume Acte S * R 0.5 OFF 0 o *exp( 0.5 ON ) BE ) * R EL 503: Semconductors

18 BJ n Logc Gates When BE ncreases such that B becomes larger than 0.4 ransstor enters Saturaton Regon 0. o E 2 Whch Logc gate ths rcut mplements? EL 503: Semconductors

19 BJ n Logc Gates hnk Whch Logc gate ths rcut mplements? EL 503: Semconductors

20 EL 503: Semconductors Small Sgnal Models Deraton : BJ must be n acte regon to use the small sgnal model be c m g be c c be be be be BE S be BE S BE S c ) *(1 ) exp( ) )exp( exp( ) exp( ) exp( B m b be be c b c b B B g r r

21 Small Sgnal Models -model g r r o m B A g m EL 503: Semconductors

22 Small Sgnal Models -model g r r e o m E A g m EL 503: Semconductors

23 ommon Emtter Amplfer Why t s called common emtter? Bypass capactors Open crcut at D Short crcut at small sgnal How to draw the small sgnal equalent crcut? EL 503: Semconductors

24 ommon Emtter Amplfer EL 503: Semconductors

25 ommon Emtter Amplfer Amplfer parameters: oltage gan (A ) = o / <Unts /> nput resstance (R n ) = / <Unts > Output resstance (R out ) = o / o s=0 <Unts > EL 503: Semconductors

26 ommon Emtter Amplfer oltage gan (A ) = o / = - g m *(r o //R // R L ) / = - g m *(R // R L ) when r o >> R and R L = - g m *(R ) when r o >> R and R L = EL 503: Semconductors

27 ommon Base Amplfer A = ro = oltage gan (A ) = o / = (R //R L )/ r e = +g m (R //R L ) = (R )/ r e = +g m (R ) when R L = EL 503: Semconductors

28 ommon ollector Amplfer (Emtter follower) A = ro = oltage gan (A ) = o / = R L / (R L + r e ) = 1 when R L = Why t s called Emtter follower? EL 503: Semconductors

Common Base Configuration

Common Base Configuration ommon Base onfguraton nput caracterstcs: s. B wt B const Output caracterstc: s. B wt const Pcture from ref [2] S. Lneykn, ntroducton to electroncs Slde [53] ommon Base Termnal caracterstcs [2] α BO FB