Review of Electronic I. Lesson #2 Solid State Circuitry Diodes & Transistors Chapter 3. BME Electronics II J.Schesser

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1 Review f Electrnic I Lessn #2 Slid State Circuitry Dides & Transistrs Chapter 3 ME Electrnics II 55

2 Dides Typical Dide VI Characteristics Frward ias Regin Reverse ias Regin Reverse reakdwn Regin v d 5 4 i d i d v d Reverse 2 breakdwn Reverse bias Frward bias regin regin regin ME Electrnics II 56

3 Ideal Dide asically, a switch Frward ias: any current allwed, dide n Reverse ias: zer current, dide ff N reverse breakdwn regin Dide ff v d i d Dide n ME Electrnics II 57

4 Hw D We Use Dides Rectifier circuits Halfwave: nly ne (psitive r negative) side f a wavefrm is passed Fullwave: wavefrm is made single sided Pwer Regulatin Wave Shaping Clipping Circuits: wavefrms are limited in amplitude Clamping Circuits: the extreme values f a wavefrm is clamped t a set value Lgic Circuits AND and OR gates ME Electrnics II 58

5 asic Semicnductr Electrnics Atmic Structure f Valence4 elements like Carbn, Silicn, Germanium, etc. have 4 valence electrns in its uter atmic shell these atms frm cvalent bnds with 4 ther atms in a lattice When the energy levels f these electrns are raised several f these bnds may becme randmly brken and a free electrn is created as a result these electrns are free t mve abut in the material similar t electrn cnductin ccurs in a metal in additin t the free electrn, a negative particle, a hle which is a psitive particle is created which als mves freely within the material. As electrns and hles mve thrugh the material, they may encunter each ther and recmbine and, thereby, becme electrically neutral This type f material is called an intrinsic semicnductr ME Electrnics II 59

6 Dped Semicnductr Material If we incrprate a small impurity f five r three valence band materials int a 4 valence band lattice, we have created an extrinsic semicnductr which is dped with an impurity ntype semicnductr Dping with five valence material (e.g. Arsenic) t create additinal free (dnr) electrns and a static psitive charged in in the cre lattice Majrity carriers are electrns; minrity carriers are hles The cncentratin f electrns in a ntype semicnductr = cncentratin f the dnr electrns the cncentratin f free hles (which is the same as the number f electrns which have randmly brken their valence bnds) ptype semicnductr Dping with three valence material (e.g., Gallium) t create additinal free (dnr) hles and a static negative charged in in the cre lattice Majrity carriers are hles; minrity carriers are electrns The cncentratin f hles in a ptype semicnductr = cncentratin f the dnr hles the cncentratin f free electrns (which is the same as the number f hles which have randmly brken their valence bnds) ME Electrnics II 60

7 PN Junctin When a ptype semicnductr is fused with a ntype, the fllwing ccurs at the junctin. ecause the cncentratin f electrns is greater n ntype side, hles frm the ptype diffuse acrss the junctin t the ntype side Likewise electrns diffuse acrss the junctin frm the ntype t the p type material These carriers recmbine and what remains are the negatively charged ins n the ptype side and psitively charged in n the ntype side. The ins which are tied t the lattice frm an electric field which prhibits the flw f carriers acrss the junctin. The area where these ins and their assciated electric field are situated is called the depletin regin since it is depleted f hles and electrns The electric field which prhibits the flw f carriers is called the barrier ptential ME Electrnics II 61

8 Reverse ias PN Junctin When an external vltage is a applied t a PN junctin such that the n type is mre psitive than the ptype, then we say that the PN junctin is reversebiased and the fllwing happens: The external vltage creates an electric field which enhances the barrier ptential and the depletin regin becmes wider since the majrity carriers are pulled away frm the junctin (e.g., the electrns in the ntype material are attracted away frm the junctin by the psitive vltage). Hwever, this applied field supprts the flw f minrity carriers acrss the junctin (e.g., the hles in the ntype material are attracted acrss the junctin by the enhanced electric field f the widened depletin regin) and when they crss the junctin they becme majrity carriers (e.g., the minrity carrier ntype hles nw becme majrity carriers nce they crss the junctin t the ptype) and are attracted away frm the junctin as described abve. Since the flw acrss the junctin is due t minrity carriers the current flw is small (this is smetimes called the reversebased leakage current). ME Electrnics II 62

9 Frward ias PN Junctin When an external vltage is a applied t a PN junctin such that the n type is mre negative than the ptype, then we say that the PN junctin is frwardbiased and the fllwing happens: The external vltage creates an electric field which ppses the barrier ptential and the depletin regin becmes smaller prvided it is larger than the vltage barrier f the depletin regin (typically, a few tenths f a vlt) This allws fr the further flw f majrity carriers acrss the junctin As the majrity carriers crss the junctin, the becme minrity carriers and then recmbine the majrity carriers n the ther side Since the flw acrss the junctin is due t majrity carriers the current flw is large. ME Electrnics II 63

10 p Depletin Regin PN Junctins Summarized Unbiased PN Junctin p n Hles Depletin Regin p Electrns Electrns n Depletin Regin Hles Reversebiased PN Junctin n Frwardbiased PN Junctin ME Electrnics II 64

11 i I D andv V S T = PN Junctins Shckley Equatin ( e 1) where i and v Shckley Equatin is called the reverse bias saturatin current, = I S T kt q v V D T v d is the called the thermal vltage and is where k is the bltzman cnstant, T is the temperature f the D i d D junctin in degrees Kelvin, i D µ amps v D vlts are the dide current and vltage, Jule/ Kelvin, and q is the magnitude f electric charge f an electrn, culmbs ME Electrnics II 65

12 iplar Junctin Transistrs Tw junctins npn r pnp Cllectrase and Emitterase iasing v E Frward iased v C Reverse iased ase i v E Cllectr C vce E Emitter npn i C i E ME Electrnics II ase i v E Cllectr C i C v CE i E E Emitter pnp 66

13 npn (pnp) JT Semicnductr Physical characteristics: ase is narrwer than the emitter Emitter is dped mre than the base Free electrn (hle) cncentratin in the emitter greater than the hle (electrn) cncentratin in base aseemitter junctin is frward biased There is a flw f electrns (hles) frm the emitter t base and hles (electrns) frm the base t emitter; hwever since the cncentratin f emitter electrns (hles) are greater than the base hles (electrns), this current is primarily made f electrns (hles) These emitter electrns (hles) becme minrity carriers in the base; hwever, since the base is narrw very little electrnhle recmbinatin ccurs in the base and these electrns (hles) are drawn twards the cllectrbase junctin Cllectrbase junctin is reverse biased When these emitter electrns (hles) reach the cllectrbase junctin, they are pulled acrss the junctin int the cllectr by the electric field due t the depletin regin ins. The rati f the electrns (hles) reaching the cllectr t the electrns (hles) prvided by the emitter is knw as α. ME Electrnics II 67

14 npn JT Electrns Electrns n p n i C Hles i E i C A small amunt f recmbinatin ccurs with the bases hles and emitter electrns C ME Electrnics II 68

15 i = α = i i E C = = β = i i i C C E i (1 α) i α i 1 α α 1 α E = JT Equatins βi ase i Cllectr C vce v E E Emitter i c =β i =α i E i E ME Electrnics II 69

16 JT Characteristics R C Vin R 50k 2k VCC 10V VCC i C amps 7.E03 6.E03 5.E03 VCC RC = 5 ma i =50 µa 40 µa I Q V 1.6V i µ amps 0 V E v E vlts I CQ = 2. 5 ma 4.E03 3.E03 2.E03 1.E03 0.E00 i V V = R V V VE DC value f i = I Q = = 20µ amps R E 30 µa Q POINT 20 µa 10 µa 0 µa v CE vlts in VCC = 10 v ME Electrnics II 70

17 Saturatin JT Regins f Operatin Active 7.E03 6.E03 5.E03 4.E03 3.E03 2.E03 1.E03 0.E00 i C amps i =50 µa 40 µa 30 µa 20 µa 10 µa 0 µa v CE vlts Cutff Cutff: bth junctins are reverse biased, i =0, v E <V E,v C = v E v CE, i C =0, v CE =VCC Active: Emitterase junctin frward biased, Cllectr ase junctin reverse biased, i >0, v E =V E, i C =βi >0, v CE =VCCi C R L Saturatin: bth junctins are frward biased, i >0, v E =V E, v C = v E v CE, v CE 0<v E, i C =VCC/R L ME Electrnics II 71

18 Small Signal Equivalent Circuits and Parameters fr the JT When the AC Prtin f the input is small arund the Q pint (<<V T in value) then we can apprximate the peratin f transistr by an equivalent circuit cnsisting f a resistr, r π =V T /I Q and a current surce, βi b, where i b is the small signal cmpnent f the base current: r π βi b C E ME Electrnics II 72

19 The JT as a Digital Switch Operating between cutff and saturatin (i.e., bypassing the active regin), the JT acts like an inverter. Frm this behavir, lgic circuits such as NOR gates can be develped ME Electrnics II 73

20 Hmewrk Prbs. 3.2, 3.3, 3.5, 3.15, 3.16, 3.17, 3.65, 3.73 Prbs. 4.4, 4.5, 4.8, 4.10, 4.20, 4.21, 4.22, 4.42 ME Electrnics II 74

Introduction to Optical Detectors (Nofziger)

Introduction to Optical Detectors (Nofziger) 1 Intrductin t Optical Detectrs (Nfziger) Optical detectrs are at the heart f mst mdern-day ptical systems. They have largely replaced the human eye r tgraic film as the detectin medium. They may be categrized