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Home , Breakdown voltage, Leakage (electronics)

CO2005: I

The Bipolar Junction (BJT)

張大中 中央大學 通訊工程系 [email protected]

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 1 Bipolar Transistor Structures

19 17 N D 10 N P 10 15 N D 10

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 2 Forward-Active Mode in the NPN Transistor

Because of the large concentration gradient in the base region, injected from the emitter diffuse across the base into the BC space-  charge region, where the E-field e sweeps them into the collector region.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 3 Currents in Emitter, Collector, and Base  Emitter Current: Exponential function of the BE  Collector Current: Ignoring the recombination in the base region (the base width is very tiny, micrometer), the collect current is proportional to the emitter injection current and is independent of the reverse-biased BC voltage. Hence, the collector current is controlled by the BE voltage.  Base Current:  BE forward-biased current iB1 N D,E N P,B  Base recombination current iB2 iC iB1,

iE iB iC iB1 iC

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 4 Common-Emitter Configuration

i C  Common-emitter current gain iB The power supply voltage Vcc iE iB iC (1)iB must be sufficiently large to keep BC junction reverse  i  i biased. C (1) E

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 5 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 6 Forward-Active Mode in the PNP Transistor

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 7 Circuit Symbols and Conventions

The arrowhead is always placed on the emitter terminal, and it indicates the direction of the emitter current.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 8 Common-Emitter Circuits

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 9 Current-Voltage Characteristics for CB Voltage  The collector current is nearly independent of the CB voltage as long as the BC junction is reverse biased.

iC  F   1 iE 1

Emitter is like a constant-current source.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 10 Current-Voltage Characteristics for CE Voltage  For forward-active mode, the BC junction must be reverse biased, which means that Vce must be greater than approximately Vbe(on). There is a finite to the curves.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 11 Early Voltage  When the current-voltage characteristic curves are extrapolated to zero current, they meet at a point on the negative voltage axis at Vce=-Va, the early voltage.  The slope of the curves indicates that the output resistance looking into the collector is finite. The resistance is not critical in the dc analysis.

1 i  C ro vCE vBE const.

VA ro  , IC

IC : the quiescent collector current

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 12 Leakage Currents

ICBO : the normal leakage current in the reverse-biased BC pn junction

ICEO : the BE current which is is induced by the forward-biased BE pn junction

ICEO ICEO ICBO I I  CBO (1)I CEO 1 CBO

Open-emitter Open-base configuration configuration

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 13  Common-Base Characteristics ForthecurvesinwhichiE 0 , breakdown beginsearlier. The carriers flowing across the junction initiates the breakdown avalanche process at somewhat lower .

Emitter is open.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 14 Breakdown Voltage  Common-Emitter Characteristics

BVCEO BVCBO ,

BVCBO BVCEO  ,n 3 ~ 6 n 

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 15 DC Analysis of Common-Emitter Circuit for NPN

VBB VBE (on) I B  and IC I B RB

VCC IC RC VCE  VCE VCC IC RC

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 16 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 17 DC Analysis of Common-Emitter Circuit for PNP

VBB VEB (on) I B  and IC I B RB

VEC VCC IC RC

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 18 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 19 Load Line

VCE VCC IC RC

VCC VCE VCE IC   5  RC RC 2

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 20 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 21 Bipolar DC Analysis Technique

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 22 Voltage Transfer Characteristics

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 23 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 24 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 25 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 26 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 27 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 28 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 29 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 30 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 31 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 32 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 33 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 34 Transistor Circuit Application:  Cutoff and Saturation Cutoff:

vI VBE (on), iB iC 0

vO VCC Saturation:

vI VCC , RB / RC 

vO VCE (sat)

vI VBE (on) iB  RB

VCC VCE (sat) ic IC (sat)  RC

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 35 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 36 Transistor Circuit Application: Digital Logic  Bipolar Inverter

 Multiple-input NOR gate

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 37 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 38 Transistor Circuit Application: Digital Logic

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 39 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 40 Single Base Resistor

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 41 Q-Point  Using the same values of the resistances, the shift of Q-point is significant due to the variation of the value of .

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 42 Voltage Divider Biasing

RTH R1 // R2 VTH I BQ RTH VBE (on) (1)I BQ RE V V (on) R2 TH BE V  V I BQ  TH CC R (1)R R1 R2 TH E

ICQ I BQ

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 43 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 44 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 45 Bias Stability

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 46 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 47 Positive and Negative Voltage Biasing

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 48 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 49 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 50 Integrated Circuit Biasing  For integrated circuits, we would like to eliminate as many resistors as possible since, in general, they require a larger surface than .

 0 I1R1 VBE (on) V

 (VBE (on) V ) I1  Reference current R1

I1 IC1 I B1 I B2 IC1 2I B2 2I 2 I  C 2 (1 )I C 2   C 2 2 I I (1 ) I C 2 1  1

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 51 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 52 Multistage Circuits

5 V  C1 I 1.12 5 B2 5 V 0.7  I  C1 B2 1012

 IB2 0.0237mA, IE2 2.39mA

VC1 0.48V, VE2 5 2 2.39 0.22V

VC2 5 1.5 2.37 1.445V 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 53 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 54 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 55