![]() Go back to equation of vo and calculate the gain vo / vs = vbe / vbe vo / vs = / vo / vs = AV = vo / vs =Ģ4 Current Gain Output side: io = vo / RC = vo / 6 Go back to equation of vo and calculate the gain vbe in terms of vs use voltage divider: vbe = * vs = vs so vs = vbeĢ3 5. Equation of vo : vo = - ( ro || RC ) gmvbe= ( 5.677) vbe = vbe 3. Vbe gmvbe RTH RC = 6 k RS = 0.5 k vS vO 5.9 k 2.74 k 105.37 k Follow the steps 1. Off - becomes short circuit off - becomes short circuit CC becomes short circuit during AC vS RTH RC voĢ2 Follow the steps 1. VCC = 12 V RC = 6 k 93.7 k 6.3 k 0.5 k β = 100 VBE = 0.7V VA = 100 V Voltage Divider biasing: Change to Thevenin Equivalent RTH = 5.9 k VTH = VĢ0 Perform DC analysis to obtain the value of ICīE loop:ĕ.9IB – = 0 IB = IC = βIB = mA Calculate the small-signal parameters r = 2.74 k, ro = k and gm = 36.5 mA/VĢ1 Emitter Grounded β = 100 VBE = 0.7V VA = 100 V vo RC RTH vS ![]() Go back to vo equation and calculate the voltage gainġ9 Emitter Grounded β = 100 VBE = 0.7V VA = 100 V the gain is a negative value Three types of common emitter Emitter grounded With RE With bypass capacitor CEġ8 STEPS OUTPUT SIDE Get the equivalent resistance at the output side, ROUT Get the vo equation where vo = - gm vbeROUT INPUT SIDE Calculate Ri Get vbe in terms of vs – eg: using voltage divider. The output is measured at the collector terminal. Determine the collector current, ICQ and then find r and ro ANSWERS: ICQ = 5.2 mA, r= k and ro = 38.5 kġ5 Voltage Gain, AV = vo / vs Current Gain, Ai = io / isĬALCULATION OF GAIN Voltage Gain, AV = vo / vs Current Gain, Ai = io / isġ7 Remember that for Common Emitter Amplifier, It is connected between Base and Emitter terminals The term gm is called a transconductance rO = small signal transistor output resistance VA is normally equals to , hence, if that is the case, rO = open circuit ro = VA / ICQ Hence from the equation of the AC parameters, we HAVE to perform DC analysis first in order to calculate them.ġ4 EXAMPLE The transistor parameter are = 125 and VA=200V. The resistance rπ is called diffusion resistance or B-E input resistance. Then:ĭC ANALYSIS AC ANALYSIS Turn off DC SUPPLY = short circuit Turn off AC SUPPLY = short circuitĩ IDQ VDQ = V + - rd id DC equivalent AC equivalentġ0 CALCULATE DC CURRENT, ID CALCULATE AC CURRENT, idĭC ANALYSIS AC ANALYSIS DIODE = MODEL 1 ,2 OR 3 CALCULATE rd DIODE = RESISTOR, rd CALCULATE DC CURRENT, ID CALCULATE AC CURRENT, idġ2 AC equivalent circuit – Small-Signal Hybrid-π Equivalent Response – sum of responses of the circuit for each input signals alone So, for linear amplifier, DC analysis is performed with AC source turns off or set to zero AC analysis is performed with DC source set to zeroĥ EXAMPLE iC, iB and iE, vCE and vBE Sum of both ac and dc componentsĦ Graphical Analysis and ac Equivalent Circuitįrom the concept of small signal, all the time-varying signals are superimposed on dc values. If the time-varying output voltage is directly proportional to and larger than the time-varying input voltage, then the circuit is a linear amplifier.Ĥ The linear amplifier applies superposition principle ![]() If a time-varying signal is superimposed on the dc input voltage, the output voltage will change along the transfer curve producing a time-varying output voltage. To use the circuit as an amplifier, the transistor needs to be biased with a DC voltage at a quiescent point (Q-point) such that the transistor is biased in the forward-active region. Presentation on theme: "Recall Last Lecture Biasing of BJT Three types of biasing"- Presentation transcript:ġ Recall Last Lecture Biasing of BJT Three types of biasingįixed Bias Biasing Circuit Biasing using Collector to Base Feedback Resistor Voltage Divider Biasing CircuitĢ Chapter 5 basic bjt amplifiers (AC ANALYSIS)īipolar transistors have been traditionally used in linear amplifier circuits because of their relatively high gain.
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