1. Submittted To: S.D MISHRA ASST.PROF CSE DEPT. Submitted By: SHIKHA KUMARI III rd SEM CSE B.E LAB

2. Three Possible Configurations of BJT Biasing the transistor refers to applying voltages to the transistor to achieve certain operating conditions. 1. Common-Base Configuration (CB) : input = V EB & I E output = V CB & I C 2. Common-Emitter Configuration (CE): input = V BE & I B output= V CE & I C output= V CE & I C 3. Common-Collector Configuration (CC) :input = V BC & I B (Also known as Emitter follower) output = V EC & I E (Also known as Emitter follower) output = V EC & I E

3. I E I C In common base configuration the base is common to both input and output hence, it is called common base configuration or CB configuration. Since base is grounded it is also called grounded base configuration. In this configuration, emitter current(I E ) is the input current and collector current(I C ) is the output current. The input signal is applied between the emitter and base whereas output is taken out from the collector and base. The ratio of collector current to the emitter current is called dc alpha of a transistor. I C /I E Therefore,  dc =-I C /I E, I c = αI E + I CBo We have, I c = αI E + I CBo, I CBo Since, I CBo is negligibly small in most practical situations,, I c = αI E We can approximately write, I c = αI E  = I C /I E or,  = I C /I E I E = I B + I C for a transistor I E = I B + I C I E = I B +(αI E + I CBo ) I E = I B +(αI E + I CBo ) I B = I E –(αI E + I CBo ) I B = I E –(αI E + I CBo ) I B = (1- α) I E – I CBo I B = (1- α) I E – I CBo I CBo I B = (1- α) I E Neglecting I CBo we can write, I B = (1- α) I E

4. Common-Base BJT Configuration Circuit Diagram: NPN Transistor +_+_ ICICICIC IEIEIEIE IBIBIBIB V CB V BE EC B V CE V BE V CB Region of Operation ICICICIC V CE V BE V CB C-B Bias E-B Bias Active IBIBIBIB =V BE +V CE ~0.7V  0V Rev.Fwd. SaturationMax~0V~0.7V -0.7V<V CE <0 Fwd.Fwd. Cutoff~0 =V BE +V CE  0V  0V Rev. None /Rev. The Table Below lists assumptions that can be made for the attributes of the common-base BJT circuit in the different regions of operation. Given for a Silicon NPN transistor.

5. I E V BE V CB input characteristics of CB configuration is plotted between input current I E and input voltage V BE with output voltage V CB can constant. I E V BE V CB the pictorial or graphical representation of input current I E with variation in input voltage V BE and different values of V CB is called input characteristics or static emitter characteristics of common base configuration.

6. ICICICIC 2 mA 4 mA 6 mA 8 mA 0.2V V BE 0.4V I E I E V BE V BE This characteristics may be used to find the input resistance of transistor. Its value is given by the reciprocal of its slope. in V BE I E R in = V BE / I E V CB constant SiGe V BE - I c (output) Characteristic Curves

7. I C V CB I E Output characteristics of CB configuration is plotted between output current I C and output voltage V CB keeping input current I E constant. I C V CB I E To pictorial or graphical representation of variation in collector current I C with output voltage V CB as different values of I E is called output characteristics of common base configuration.

8. Saturation Region IEIEIEIE ICICICIC V CB Active Region Cutoff I E = 0 0.8V2V4V6V8V mA 2 4 6 I E =1mA I E =2mA Breakdown Reg. V CB - I c (output) Characteristic Curves