DC Biasing Of BJTsDC Biasing Of BJTs DC Biasing - Hacettepe
DC Biasing of BJTsContentsDC Biasing of BJTsDC BiasingDC Biasing of BJTsDC Biasing of BJTsThree States of OperationBJT DC AnalysisDC Biasing CircuitsBiasing refers to the DC voltages applied to the transistor to put it into active mode, sothat it can amplify the AC signal.The DC input establishes an operating point or quiescent point called the Q-point.Proper DC biasing should try to set the Q-point towards the middle of active region, e.g.,Point B in the gure below.Fixed-Bias CircuitEmitter-Stabilized Bias CircuitVoltage Divider Bias CircuitDC Bias with Voltage FeedbackVarious Di erent Bias Circuitspnp TransistorsBias StabilizationStability FactorsStability of Transistor Circuits with Active ComponentsPractical ApplicationsRelay DriverTransistor SwitchTransistor Switching NetworksLogic GatesCurrent MirrorVoltage Level IndicatorDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-20171 / 59Three States of OperationIActive: Operating state of the ampli er: IC βIB .Base-Emitter (BE ) junction: forward-biased (ON).Base-Collector (BC ) junction: reverse-biased (OFF).ICut-O : The ampli er is basically o . There is no current, i.e., ICBase-Emitter (BE ) junction: reverse-biased (OFF).Base-Collector (BC ) junction: reverse-biased (OFF).ISaturation: The ampli er is saturated. Voltages are xed, e.g., VCE VCE(sat) 0 V.Output is distorted, i.e., not the same shape as the input waveform.Base-Emitter (BE ) junction: forward-biased (ON).Base-Collector (BC ) junction: forward-biased (ON).DC Biasing of BJTs15-Mar-20172 / 59BJT DC AnalysisBJT DC AnalysisProper DC biasing sets the BJT transistor into the active state, so that it can amplifythe AC signal. Let us remember the states of the transistor:ELE230 Electronics IELE230 Electronics IDC Biasing of BJTsThree States of OperationDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.) IB IE 0 A.15-Mar-20173 / 59DC Biasing Circuits1. Draw the DC equivalent circuit (signal frequency is zero, i.e., f 0)a) Capacitors are open circuit, i.e., XC .b) Kill the AC power sources (short-circuit AC voltage sources and open-circuit ACcurrent sources).c) Inductors are short circuit or replaced by their DC resistance (winding resistance) ifgiven, i.e., XL 0.2. Write KVL for the loop which contains BE junctiona) Take VBE VBE(ON ) to ensure the transistor is ON (or not in the cut-o state).Note: For a pnp transistor, VEB VBE(ON ) .b) Determine the base current IBQ (or emitter current IEQ ).3. Write KVL for the loop which contains CE terminalsa) Assume the transistor is in the active state and take ICQ βIBQ (or ICQ αIEQ ).b) Calculate VCEQ .c) If VCEQ VCE(sat) then the transistor is in the saturation (SAT) state (i.e., ICQ 6 βIBQ ), so take VCEQ VCE(sat) and recalculate ICQ .NOTE: Normally, a BJT should not be in the saturation state if it is used as anampli er.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTsDC Biasing Circuits15-Mar-20174 / 59DC Biasing CircuitsFixed-Bias CircuitFixed-bias circuit is given belowMost common four common-emitter biasing circuits are given below1. Fixed-Bias Circuit2. Emitter-Stabilized Bias CircuitLet us start DC analysis by drawing the DC equivalent circuit as shown below3. Voltage Divider Bias Circuit4. DC Bias with Voltage FeedbackDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-20175 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-20176 / 59
DC Biasing of BJTsDC Biasing CircuitsDC Biasing of BJTsBase-Emitter LoopDC Biasing CircuitsCollector-Emitter LoopLet us continue with the CE loop shown belowLet us continue with the BE loop shown belowWriting KVL on the BE loopWriting KVL on the CE loop (i.e., DC load-line equation)VCC IC RC VCE 0VCC IB RB VBE 0and given (assuming BJT is in active state)and given VBE VBE(ON ) , we obtain IBQ asIBQ Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ICQ βIBQVCC VBE(ON )RBELE230 Electronics IDC Biasing of BJTswe obtain VCEQ asVCEQ VCC ICQ RC15-Mar-20177 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)DC Biasing CircuitsDC Biasing of BJTsSaturationELE230 Electronics IDC Biasing of BJTs15-Mar-20179 / 5915-Mar-20178 / 59DC Biasing CircuitsFor the xed-bias con guration shown below, the resulting saturation current (i.e.,maximum current) IC(sat) is given byThe term saturation is applied to any system where levels have reached their maximumvalues. A saturated sponge is one that cannot hold another drop of water. For atransistor operating in the saturation region, the current is a maximum value for theparticular design.Note that it is in a region where the characteristic curves join and the collector-to-emittervoltage is at or below VCE(sat) . If we approximate the curves of the left gure by thoseappearing in the right gure, then the saturation voltage VCE(sat) is assumed to be 0 V,i.e,VCE(sat) 0VDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IIC(sat) IC(max) Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)DC Biasing CircuitsVCC VCE(sat)RCELE230 Electronics IDC Biasing of BJTsVCC RC15-Mar-201710 / 59DC Biasing CircuitsDC Load LineDC load line equation comes from KVL equation in the CE loop (i.e., output loop). Forthe xed-bias circuit, DC load line equation is given byVCE VCC IC RCLet us draw the load line over output characteristics curve as shown below. Theintersection of the load-line with the output characteristics curve (determined by the basecurrent IBQ ) is the operating point, i.e., Q-point.Example 1: For the gure above, calculate all DC currents and voltages.Solution: Let us nd IBQ , ICQ and VCEQ as followsIBQ VCC VBE(ON )RB 12 0.7 47.08 µA,240kICQ βIBQ (50)(47.08µ) 2.35 mA,VCEQ VCC ICQ RC 12 (2.35m)(2.2k) 6.83 V.As VCEQ VCE(sat) 0 V, transistor is in the active state. Let us also prove it byshowing VBCQ VBC(ON ) 0.7 V as followsVBCQ VBQ VCQ VBEQ VCEQ 0.7 6.83 6.13 V 0.7 V.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-2017I11 / 59The Q-point is the operating point where the value of RB sets the value of IBQ thatcontrols the values of VCEQ and ICQ .Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201712 / 59
DC Biasing of BJTsDC Biasing CircuitsDC Biasing of BJTsDC Biasing CircuitsThe E ect of IB on the Q-PointMovement of the Q-point with increasing level of IB (or decreasing level of RB ) is shownbelow.Fixed-bias load line equation: VCE VCC IC RCThe load line end points are the SATURATION and CUTOFF points, i.e.,I IC(sat)end point (on the current axis):IC VCC /RCI VCE(cutoff )VCE 0 Vend point (on the voltage axis):VCE VCCIC 0 mADr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201713 / 59DC Biasing CircuitsDC Biasing of BJTs15-Mar-201714 / 59DC Biasing CircuitsThe E ect of VCC on the Q-PointE ect of an increasing level of RC on the load line (slope decreases with increasing RC )and the Q-point is shown below.ELE230 Electronics IELE230 Electronics IDC Biasing of BJTsThe E ect of RC on the Q-PointDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)15-Mar-201715 / 59DC Biasing CircuitsE ect of an decreasing level of VCC on the load line (end points gets smaller withdecreasing VCC ) and the Q-point is shown below.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201716 / 59DC Biasing CircuitsEmitter-Stabilized Bias CircuitAdding a resistor to the emitter circuit stabilizes the bias circuit, as shown below.Example 2: For the xed-bias load line above, calculate VCC , RC and RB .Solution: From the gure, IBQ 25 µA. So, let us nd VCC , RC and RB as followsLet us start DC analysis by drawing the DC equivalent circuit as shown belowVCC VCE(cutoff ) 20 V,RC RB VCC20 2 kΩ,IC(sat)10mVCC VBE(ON )Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)IBQ 20 0.7 772 kΩ.25µELE230 Electronics I15-Mar-201717 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201718 / 59
DC Biasing of BJTsDC Biasing CircuitsDC Biasing of BJTsBase-Emitter LoopDC Biasing CircuitsSimilarly, we can obtain IEQ directly from the gure below, or dividing the denominatorof the IBQ by (β 1)Let us continue with the BE loop shown belowas followsWriting KVL on the BE loopIEQ VCC IB RB VBE IE RE 0. . . as VBE VBE(ON )VCC IB RB VBE(ON ) (β 1)IB RE 0,IE (β 1)IBwe obtain IBQ asandin active modeIIBQ Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)VCC VBE(ON )VCC VBE(ON )RB REβ 1It is generally better to calculate IEQ directly to reduce the number of calculations,especially when there is an emitter resistor RE is connected.RB (β 1)REELE230 Electronics IDC Biasing of BJTs15-Mar-201719 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)DC Biasing CircuitsELE230 Electronics IDC Biasing of BJTsCollector-Emitter Loop15-Mar-201720 / 59DC Biasing CircuitsDC Load LineLet us continue with the CE loop shown belowDC load line equation comes from KVL equation in the CE loop (i.e., output loop). Forthe emitter-stabilized bias circuit, DC load line equation is given byVCE VCC IC (RC RE )Let us draw the load line over output characteristics curve as shown below.Let us write down the KVL equation on the CE loopVCC IC RC VCE IE RE 0. . . as IC αIE IEVCC IC RC VCE IC RE 0As ICQVCC IC (RC RE ) VCE 0 βIBQ IEQ in active mode, weobtain. . . DC loadVCEQ asin active modeline equationELE230 Electronics IDC Biasing of BJTsVCCRC REthe value of RBIC(sat) VCEQ VCC ICQ (RC RE )Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Here, VCE(cutoff ) VCC and IC(sat) is given byI15-Mar-201721 / 59The Q-point is the operating point wherethat controls the values of VCEQ and ICQ .Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)DC Biasing Circuitsand RE sets the value of IBQELE230 Electronics IDC Biasing of BJTs15-Mar-201722 / 59DC Biasing CircuitsImproved Biased StabilityStability refers to a condition in which the currents and voltages remain fairly constantover a wide range of temperatures and transistor beta (β ) values.IAdding RE resistor to the emitter improves the stability of a transistor.Example 3: For the gure above, calculate all DC currents and voltages.Solution: Let us nd IBQ , ICQ and VCEQ as followsIBQ VCC VBE(ON )RB (β 1)RE 20 0.7 40.13 µA,430k (50 1)(1k)ICQ βIBQ (50)(40.13µ) 2.01 mA, VCC ICQ (RC RE ) 20 (2.01m)(2k 1k) 13.97 V.VCEQ As VCEQ 0 V (VCE(sat) ), transistor is in the active state.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201723 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201724 / 59
DC Biasing of BJTsDC Biasing CircuitsDC Biasing of BJTsVoltage Divider Bias CircuitBase-Emitter Loop (Exact Analysis)Voltage divider bias circuit is given belowLet us transform the BE loop circuit shown on the left below to the Thévenin simpli edcircuit on the right belowwhere the Thévenin voltage VBB and Thévenin resistance RBB are calculated as followsLet us start DC analysis by drawing the DC equivalent circuit as shown belowDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTsDC Biasing Circuits15-Mar-201725 / 59R2VCCR1 R2 R1 R2VBB . . . fromthe gure on the left belowRBB. . . fromthe gure on the right belowDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)DC Biasing CircuitsELE230 Electronics IDC Biasing of BJTs15-Mar-201726 / 59DC Biasing CircuitsBase-Emitter Loop (Approximate Analysis)IEQ VBB VBE(ON )RBB /(β 1) REIf we look at the IEQ equation above, we see that if REIEQ Writing KVL on the Thévenin equivalent BE loop shown abovewhere VBB VBB IB RBB VBE IE RE 0VBB IB RBB VBE(ON ) (β 1)IB RE 0,we obtain IBQ asIBQ . . . as VBE VBE(ON )andIE (β 1)IB in active modeIDC Biasing of BJTsRE.Assuming R1 R2 , we know that (R1 R2 ) R2 . So, the condition above can befurther simpli ed toβRE 10R2 .VBB VBE(ON )RBB REβ 1ELE230 Electronics IVBB VBE(ON )(β 1)RE 10(R1 R2 ).RBB (β 1)REIEQ , equation simpli es toApproximate approach can be used when (β 1)RE RBB . Approximate analysiscondition can be rewritten asVBB VBE(ON )Similarly, we obtain IEQ asDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)R2VR1 R2 CCRBBβ 1I15-Mar-201727 / 59DC Biasing CircuitsSatisfying this condition means that we can safely ignore the base current IB in the DCequivalent circuit and apply the voltage divider rule between R2 and R1 .Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201728 / 59DC Biasing CircuitsCollector-Emitter Loop and DC Load LineIAnalysis on the CE loop (i.e., output loop), is the same as the CE loop analysis of theemitter-stabilized circuit. So, VCEQ is given byVCEQ VCC ICQ (RC RE )where ICQ IEQ .ISimilarly, DC load line analysis is also the same as the DC load line of theemitter-stabilized circuit. So, DC load line equation is given byVCE VCC IC (RC RE )Example 4: For the gure above, calculate all DC currents and voltages using both exactand approximate analysis.Solution: Let us rst nd the Thévenin voltage VBB and resistance RBB as followsR23.9kVCC 22 2 V,R1 R239k 3.9k R1 R2 3.9k 39k 3.55 kΩ.VBB RBBDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201729 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201730 / 59
DC Biasing of BJTsDC Biasing CircuitsDC Biasing of BJTsDC Biasing CircuitsDC Bias with Voltage FeedbackAnother way to improve the stability of a bias circuit is to add a feedback path fromcollector to base as shown belowNow, let us calculate IBQ , ICQ and VCEQ as followsIEQ VBB VBE(ON ) RBB /(β 1) RE2 0.7 0.85 mA,3.55k/(140 1) 1.5kICQ IEQ 0.85 mA, VCC ICQ (RC RE ) 22 (0.85m)(10k 1.5k) 12.23 V.VCEQ Let us start DC analysis by drawing the DC equivalent circuit as shown belowAs βRE 10R2 (i.e., 210 kΩ 39 kΩ), we can use the approximate analysis and ignoreIB and RBB as followsIEQ VBB VBE(ON )RE 2 0.7 0.87 mA,1.5kICQ IEQ 0.87 mA,VCEQ VCC ICQ (RC RE ) 22 (0.87m)(10k 1.5k) 12 V.We see that approximate analysis provides close values to the exact analysis. Thedi erences in ICQ and VCEQ are only 0.02 mA and 0.23 V, respectively.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201731 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)DC Biasing CircuitsELE230 Electronics IDC Biasing of BJTsBase-Emitter Loop15-Mar-201732 / 59DC Biasing CircuitsCollector-Emitter LoopLet us continue with the BE loop shown belowLet us continue with the CE loop shown belowWe can write KVL equation on the BE loop noting that IC0 IC IB IELet us write down the KVL equation on the CE loop noting that IC0 IC IB0VCC ICRC IB RF VBE IE RE 0VCC IE RCIE RF VBE(ON ) IE RE 0,β 1and we obtain IEQ asIEQ Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.). . . as VBE VBE(ON )VCC VBE(ON )RF (RC RE )β 1ELE230 Electronics IDC Biasing of BJTsIBIE β 1in active mode. . . as IC IEVCC IC RC VCE IC RE 0AsVCC IC (RC RE ) VCE 0. . . DC IEQ in active mode, we obtain VCEQ asICQ 0and IC in active mode ICload line equationVCEQ VCC ICQ (RC RE )15-Mar-201733 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)DC Biasing CircuitsELE230 Electronics IDC Biasing of BJTsDC Load LineI0VCC ICRC VCE IE RE 0and15-Mar-201734 / 59DC Biasing CircuitsVarious Di erent Bias CircuitsNote that IC0 IE , andIC IEin active mode (and β is high).ISo, DC load line analysis is the same as the DC load line of the emitter-stabilized circuit.So, DC load line equation is given byVCE VCC IC (RC RE )Example 5: For the gure above, calculate all DC currents and voltages.Solution: Let us nd IEQ , ICQ and VCEQ as followsIEQ 0 VBE(ON ) VEERB /(β 1) RE 20 0.7 4.16 mA,240k/(90 1) 2kICQ IEQ 4.16 mA,VCEQ 0 IEQ RE VEE 20 (4.16m)(2k) 11.68 V.As VCEQ VCE(sat) 0 V, transistor is in the active state.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201735 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201736 / 59
DC Biasing of BJTspnpDC Biasing CircuitsDC Biasing of BJTsDC Biasing CircuitsTransistorsThe analysis for pnp bias transistor circuits is the same as that for npn transistor circuits.The only di erences are that1. Currents are owing in the opposite direction.2. Voltages have opposite polarity, e.g., VEB VBE(ON ) 0.7 V in the active mode.Example 6: For the gure above, calculate all DC currents and voltages.Solution: As βRE 10R2 , i.e., 132 kΩ 100 kΩ, we can ignore the base current IB anduse the approximate approach. Thus, we can nd VBB , IEQ , ICQ and VCEQ as followsR210kVCC ( 18) 3.16 VR1 R247k 10k0 0.7 ( 3.16)2.460 VEB VB 2.24 mA, RE1.1k1.1k IEQ 2.24 mA, VB IEQICQVECQ 0 ICQ (RC RE ) VCC (2.24m)(2.4k 1.1k) ( 18) 10.16 V.As VECQ VCE(sat) 0 V, transistor is in the active state.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201737 / 59Bias Stabilization β15-Mar-201738 / 59Bias StabilizationVariation of the transistor parameters with temperature causes a shift in the operatingpoint (i.e., Q-point).Variation of three BJT (Si) parameters (ICO , β and VBE(ON ) ) with temperature aresummarized belowICOELE230 Electronics IDC Biasing of BJTsBias StabilizationT Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ICO β Figures below (at 25 C on the left and at 100 C on the right) show the shift of theQ-point (or DC bias point) due to temperature change for a xed-bias circuit.VBE(ON ) (reverse saturation current)doubles in value for every 10 C(transistor current gain) increases with increasing temperatureVBE(ON ) (forward bias potential of the base-emitter junction)decreases about 2.5 mV per 1 C increase in temperatureDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201739 / 59at 25 CDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Bias StabilizationELE230 Electronics IDC Biasing of BJTsStability FactorsStability of the collector current IC depends on the stability of several parameters likeICO , β , VBE(ON ) , VCC , RB , RC , etc.at 100 C15-Mar-201740 / 59Bias StabilizationDerivation of Stability Factors (Voltage-DividerBias Circuit)A stability factor S is de ned for each of the parameters a ecting bias stability as follows:SICO Sβ SVBE(ON ) IC IC ICO ICO IC IC β β IC VBE(ON )β,VBE(ON ) ,.constantICO ,VBE(ON ) ,.constant IC VBE(ON )ICO ,β,.constantLet us write down the active mode collector current and BE -loop KVL equations for thecircuit shown above,We know that di erential dIC is given by the linear map of parameter di erentials asfollowsdIC IIC βIB (β 1) ICO IC IC ICdICO dβ dVBE(ON ) · · · ICO β VBE(ON )VBB IB RBB VBE(ON ) (IB IC )REThus, we obtain the collector-current change IC using the stability factors as follows IC SICO ICO Sβ β SVBE(ON ) VBE(ON )Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-2017Combining the two equations above, we obtain the expression for IC asIC 41 / 59 (β 1) (RBB RE )βVBB VBE(ON ) ICORBB (β 1) RERBB (β 1) REDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201742 / 59
DC Biasing of BJTsIC Bias StabilizationDC Biasing of BJTsBias StabilizationUsing the simpli ed IC equation we can express IC1 and IC2 as follows (β 1) (RBB RE )βVBB VBE(ON ) ICORBB (β 1) RERBB (β 1) RE β1VBB VBE(ON )RBB (β1 1) RE β2 VBB VBE(ON ) RBB (β2 1) REIC1 1. From the IC equation above, let us derive SICO SICO IC ICOSVBE(ON ) IC βIC IC2RBB RE (β 1)RBB (β 1) RE2. From the IC equation above, let us derive SVBE(ON ) 3. In order to derive Sβ as IC VBE(ON )Thus, using the equations above, let us obrain the ratio βRBB (β 1) REFrom the equation above, we can obtain the ratio β β2 β1 asELE230 Electronics IThus, as Sβ DC Biasing of BJTs43 / 59SICO (β 1)β 1(β 1) RE1 RB45 / 59ICOβ0.02 nA200.85 V25 C0.1 nA500.65 V100 C20 nA800.48 V175 C3.3 µA1200.30 V1 1(β2 1) RCERF15-Mar-201746 / 59Bias Stabilizationa. Let us calculate the stability factors for the xed-bias circuitVBE(ON )SICO β 1 51IC12m 0.04 mAβ150 β 50 0.21 mΩ 1RB240kSβ SVBE(ON )a. Fixed-bias with RB 240 kΩ and IC1 2 mA,b. Voltage-divider bias with RE 4.7 kΩ, RBB /RE 2 and IC1 2 mA. IC (51)(19.9n) (0.04m)(30) ( 0.21m)( 0.17) 1.02µ 1.2m 0.036mRBBSICO 1 2 3 1 RE IC1RBB2m Sβ 1 (1 2) 1.5 µAβ1 β2RE(50)(80) 1 1 1SVBE(ON ) 0.21 mΩRE4.7k ICO ICO2 ICO1 20n 0.1n 19.9 nA β β2 β1 80 50 30 VBE(ON ) VBE(ON )2 VBE(ON )1 0.48 0.65 0.17 VWe are goiung to calculate IC using IC SICO ICO Sβ β SVBE(ON ) VBE(ON )15-Mar-2017Thus, IC is given by 1.236 mAThat means, for the xed-bias circuit IC increases to 3.236 mA at 100 C from 2 mA.b. Let us calculate the stability factors for the voltage-divider bias circuitSolution: From the table above, let us rst calculate ICO , β and VBE(ON )ELE230 Electronics Iβ 1(β 1) RCERFELE230 Electronics IDC Biasing of BJTsExample 7: Find and compare the collector current change IC when the temperaturerises from 25 C to 100 C for the transistor de ned by the table above for the followingbias arrangements.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Bias Stabilization 65 C1 βRF (β 1) RCEIC1IC1RF RCE Sβ β1 RF (β2 1) RCEβ11(β2 1) RE1 RBTemperatureRF RCE RF (β 1) RCESVBE(ON ) SVBE(ON ) DC Biasing of BJTsBias StabilizationD. For the voltage-feedback bias circuit, i.e., RBB RF , replacing RE withRCE RC RE and RF RCE , the stability factors are given byB. For the emitter-stabilized bias circuit, i.e., RBB RB and RB RE , the stabilityfactors are given by15-Mar-201744 / 59RBB RE 1 RBB RBB (β 1) RERE β 1 SVBE(ON ) RBB (β 1) RERE IC1IC1RBB RERBB Sβ 1 β1 RBB (β2 1) REβ1 β2RE βRBIC1Sβ β1ELE230 Electronics I15-Mar-2017SICO (β 1)SICO β 1 βRB (β 1) REIC1RB RE IC1Sβ β1 RB (β2 1) REβ1ELE230 Electronics IDC Biasing of BJTsSVBE(ON ) Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)IC 1RBB REβ1 RBB (β2 1) REC. For the voltage-divider bias circuit with (β 1)RE 10RBB , the stability factors aregiven byA. For the xed-bias circuit, i.e., by substituting RE 0 and RBB RB , the stabilityfactors are given byRB RE RB (β 1) REby using IC IC2 IC1 and IC β Bias StabilizationStability Factors for Other Bias CircuitsSICO (β 1) IC βSβ 15-Mar-2017 IC βIC 1RBB RE IC ββ1 RBB (β2 1) RE βVBB VBE(ON ) (β 1) REDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)asIC2 IC1β2 β1RBB RE IC1β1RBB (β2 1) REas, let us rst simplify IC equation by letting ICO 0RBBIC2 IC1IC147 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201748 / 59
DC Biasing of BJTsBias StabilizationDC Biasing of BJTsStability of Transistor Circuits with ActiveComponentsThus, IC is given by IC (3)(19.9n) (1.5µ)(30) ( 0.21m)( 0.17) 0.060µ 0.045m 0.036mVBE 0.081 mAThat means, for the voltage-divider bias circuit IC increases to 2.08 mA at 100 C fromMost of the improvement comes from the reduction in Sβ .2 mA.IBias Stabilization compensationby using a reverse-biased diode at the emitterThese two results show that voltage-divider bias circuit is much more stable than thexed-bias circuit. In other words, adding RE resistor to the emitter leg of the transistorstabilizes the bias circuit.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTsICO 15-Mar-201749 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Bias StabilizationELE230 Electronics IDC Biasing of BJTs15-Mar-201750 / 5915-Mar-201752 / 59Practical ApplicationsPractical Applicationscompensationby replacing R2 with a reverse-biased diodeRelay DriverTransistor SwitchTransistor Switching NetworksLogic GatesCurrent MirrorICcompensation (without RE ) Voltage Level Indicatorby using a current mirrorDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201751 / 59Practical ApplicationsDr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTsRelay DriverPractical ApplicationsTransistor SwitchA transistor can be used as a switch to control the ON and OFF states of the light-bulb inthe collector branch of the circuit as shown below.When the transistor turns OFF, a high voltage (given by vL L (diL /dt)) is inducedacross the coil as shown above. If its magnitude exceeds the maximum ratings of thetransistor, then the semiconductor device will be permanently damaged.This destructive action can be subdued by placing a diode across the coil as shown below.Now, when the transistor turns o , the voltage across the coil will reverse and willforward-bias the diode, placing the diode in its ON state (hence protecting the transistor).Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201753 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201754 / 59
DC Biasing of BJTsPractical ApplicationsDC Biasing of BJTsTransistor Switching NetworksPractical ApplicationsThe total time required for the transistor to switch from the OFF to the ON state isdesignated as ton , and he total time required for a transistor to switch from the ON tothe OFF state is referred to as toff as shown below. ton and toff are de ned byton tr tdtoff ts tf10% to 90% of the output, tdwhere tr is the rise time fromis the delay time between thechanging state of the input and the beginning of a response at the output, ts is thestorage time and and tf the fall time from 90% to 10% of the output.Transistors can also be used as switches for computer and control applications. Thecircuit shown above can be employed an inverter in computer logic circuitry.Inversion process requires that the Q-point switch from cuto (Vo VCE(cutoff ) 5 V)to saturation (Vo VCE(sat) 0 V) along the load line depicted below.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201755 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)Practical ApplicationsELE230 Electronics IDC Biasing of BJTsLogic Gates15-Mar-201756 / 59Practical ApplicationsCurrent MirrorThe current mirror shown below is a DC circuit in which the current through a load iscontrolled by a current at another point in the circuit. That is, the current through theload is indepedent of the load.The gure above shows a BJT logic OR gate, and similarly The gure below shows a BJTlogic AND gate.Homework 1: For the gure above, show that the load current is equal to the loadcontrol current and given byIL Icontrol VCC VBE(ON )Rwhere the transistors are identical (Q1 Q2 ), i.e., VBE1 (ON ) VBE2 (ON ) VBE(ON )and β1 β2 β , and current gain β is high, e.g., β 100.Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics IDC Biasing of BJTs15-Mar-201757 / 59Practical ApplicationsVoltage Level IndicatorThe voltage level indicator circuit uses a green LED to indicate when the source voltage isclose to its monitoring level of 9 V. The potentiometer is set to establish 5.4 V at thepoint indicated below. The result is su cient voltage to turn on both the 4.7 V Zener andthe transistor and establish a collector current through the LED su cient in magnitude toturn on the green LED. The LED will immediately turn o , revealing that the supplyvoltage has dropped below 9 V or that the power source has been disconnected (i.e., whenthe voltage set up by the voltage divider circuit drops below 5.4 V).Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201759 / 59Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-201758 / 59
DC Biasing Circuits Most common four common-emitter biasing circuits are given below 1.Fixed-Bias Circuit 2.Emitter-Stabilized Bias Circuit 3.Voltage Divider Bias Circuit 4.DC Bias with Voltage Feedback Dr. U. Sezen & Dr. D. Gökçen (Hacettepe Uni.)ELE230 Electronics I15-Mar-2017 5 / 59 DC Biasing of BJTsDC Biasing Circuits Fixed-Bias Circuit
DC Biasing of BJTsDC Biasing of BJTs DC Biasing Biasing refers to the DC voltages applied to the transistor to put it into active mode , so that it can amplify the AC signal. The DC input establishes an operating point or quiescent point called the Q-point . Proper DC biasing should try to set the Q-point towards the middle of active region, e.g.,
predefined DC sources and rest of the design are related with these sources i.e., global biasing. Our method separates the nonlinear components from the limitations of global biasing [3]. Verhoeven [6] presents a method for biasing amplifiers and in this method, biasing design is performed linearly until the end except for the transistors.
What is transistor DC biasing ? Biasing is selec3on of opera3ng point (Quiescent point) to operate a transistor in a desired region (Ac3ve, cutoff, satura3on) Biasing Circuit: The circuitry which provides the necessary condi3ons of transistor biasing is known as biasing circuit.
Chapter 4 DC Biasing-BJTs. Biasing Biasing: TThe DC voltages applied to a transistor in order to turn it on so that it can amplify the AC signal. . DC Bias with Voltage FeedbackDC Bias with Voltage Feedback Another way to improve the stabilityimprove the stability of a bias circuit is to
Biasing Circuit Biasing Circuit Biasing circuit uses same V . Very practical methods for biasing the BJTs (or MOSFETs) can be used . 4. Common Emitter with R E / Common Source with R S 5. Cascode (actually CE:CB or CS:CD cascade) 6. Darlington (special CE:CE or CS:CS cascade)
19 Transistor Biasing and Stabilization - Operating point, DC & AC load lines, Summarize Operating point, DC & AC load lines 20 Biasing - Fixed Bias Illustrate fixed bias 21 Self Bias Illustrate self bias 22 Bias Stability Illustrate stability 23 Problems and revision on biasing methods. Solve different biasing methods
sizing, adaptive body biasing, and adaptive supply voltage biasing. Because joint timing-leakage optimization is ofprimary concern, adaptive body bias may be the most useful tool. It has been demonstrated [7, 11] that body biasing can be employed as an extremely effective knob to perform post silicon optimization and
Akuntansi manajemen mempunyai peranan besar dalam perusahaan, yaitu membantu pihak pihak internal (direktur utama dan masing masing tingkatan manajer dalam setiap unit/departemen) dalam pengambilan keputusan. Oleh karena itu, akuntansi manajemen yang akan kita pelajari dalam buku ini akan membahas hal hal sebagai berikut: 1. Konsep dan fungsi biaya Pihak manajemen dapat memahami berbagai .
