Practical Biasing Design For Analog Circuits - IJERT
International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 7, July - 2014Practical Biasing Design for Analog CircuitsRohith Krishnan R1 & S. Krishnakumar 2School of Technology & Applied SciencesMahatma Gandhi University Regional CentreEdappally, Kochi, IndiaAbstract—A new method for the biasing design of analogcircuits is presented in this article. In this method, theproperties of operational amplifiers are well exploited, and it isuseful for the biasing design of circuits containing non-linearcomponents like diodes, BJTs, FETs etc. The method uses acombination of fixators, norators and nullators, whereoperational amplifiers are used as nullator plus norator (orsimply nullor). As examples, a diode circuit, a BJT circuit anda JFET circuit are shown which are designed using theproposed method for some given critical specs. Application ofcurrent mirror as a current source, and its design using theproposed method are also discussed in this paper.I.currentsources;INTRODUCTIONfixators;The design of analog circuits involves two steps, viz.the AC performance design and DC biasing design. Inperformance design, active devices are replaced with theirsmall signal model at the desired operating conditions. Afterthe completion of AC design, DC biasing design should bedone, which defines the DC supply values keeping operatingconditions of the non-linear components and the circuitperformance unchanged [1]. The proposed method is to easethe task of second step, which is biasing design.The main point of biasing design is to fix those criticalspecs [1] at some required values. Critical specs means thoseparameters, which decide the operation of a circuit. Forexample operating point of a common emitter configurationis determined by collector current IC and collector to emittervoltage VCE [2]. Therefore, in the case of a common emitteramplifier, IC and VCE are the critical specs. However, theselections of critical design specs are purely depend on thecircuit used. That is, in a multistage amplifier, more than onetransistor has to be used and not all of them may be criticalcomponents. Therefore, the number of critical specs pertransistors may not be two. All that is important is to decidewhich specs are critical and which are not. Knowledge andefficiency of the designer are checked at this stage. We havea number of critical specs while we are starting a circuitdesign. However, not all of them are bias based. Thoseparameters, which can avoid signal distortion and deal withnonlinearity, are considered as bias based specs.Once we find the operating points or critical specs for aparticular circuit operation, the next step is biasing design.Traditionally, the biasing design includes approximationsand sometimes we have to neglect certain parameters,otherwise we require a number of iterations to reach at thefinal design. This is because traditional methods take theIJERTV3IS070787Verhoeven [6] presents a method for biasing amplifiersand in this method, biasing design is performed linearly untilthe end except for the transistors. Biasing of transistor isdone separately at the last stage of the designing process.Controlled sources are used to isolate non-linear parts fromrest of the circuit. There is a time consuming iterations toreach at the final design, and controlled sources are removedat this stage.In the method proposed by Hashemian [3,4], non-lineardevices are DC isolated and locally bias them for the desiredoperating conditions. It results in larger number of scatteredDC sources. Voltage dividing, current mirroring and othersource transformation techniques are used to reduce theirnumber to one or two sources, but it is a time consuming andtedious task. Hashemian [1,7] introduced a new technique tocut down the number of steps for a targeted biasing and ituses Fixator-Norator pairs. Fixators and norators aretheoretical two terminal devices and are used in pairs. Idealcontrolled sources with very high gain are used to model thepairs.IJERTKeywords—Biasing design;nullors; operational amplifiers.circuit as a whole with no separation between linear and nonlinear components; therefore, the design becomes complex[1], [3-5]. In addition, traditional methods use one or twopredefined DC sources and rest of the design are related withthese sources i.e., global biasing. Our method separates thenonlinear components from the limitations of global biasing[3].In our method, operational amplifiers are used insteadof ideal controlled sources. Two important tools used hereare voltage fixator and current fixator using op-amp. We canmodel the non-linear device partially or completely [1,7]. Forpartial modeling, the non-linear device is placed in the circuitand using our tools, we fix those critical specs; after thedesign process, our tools are removed to obtain the finalcircuit. In this process, we actually freeze those port values atthe desired level. For some applications, all the operatingconditions of a non-linear device, viz. transistor theparameters such as VCE, VBE, IC, and IB are critical. In suchcases, we have to remove the transistor (i.e., non-lineardevice) from the circuit and instead place its fixator model.As the biasing design is completed, our tools are removedand they are replaced with original transistor. This iscomplete modeling. A mixture of partial and completemodeling is also possible.The proposed method eliminates all the theoreticalcomponents and it does not require any circuit simulator.Circuits can be designed as simple as we do practical worksin our electronics lab with familiar components. The addedbenefit is that we design the circuit using the actualwww.ijert.org910
International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 7, July - 2014components we like to use in our circuit and at the actualroom temperature. So our design becomes more accurate.Operational amplifiers play the main role in the proposedmethod, which can represent nullator and norator (i.e.nullor). Operational amplifiers act as placeholders for biassupporting components. For each critical spec, there shouldbe a bias-supporting component (DC current source, DCvoltage source or power conducting components likeresistors) in the circuit, which can control that parameter.That means we can vary a parameter by simply adjusting thevalue of corresponding bias-supporting component.Sometimes more than one component has effect on the sameparameter but the designer has to select the proper one basedon the circuit requirements. The designer can select onecomponent and adjust its value with the help of proposedmethod to meet the required design. As discussed, he/she hasmany other options than the selected one. However, thedifference is that each component affects the ACperformance design differently. The operational amplifiersand its supporting components are added in our method fordesigning only. They are removed as the design has beencompleted.II.DESIGNING TOOLSIn our method, operational amplifier is used as nullor.If it is used in a circuit, the circuit around the op-amp(nullor) determines the output of op-amp such a way that itsinput forced to zero. That means nullor output can take anyvalue so that its input equals zero.Using the basic structures of fixators in Fig.1, we candevelop two new tools, voltage fixator and current fixatorusing op-amp. The usage of these tools in a circuit is asshown in Fig.3. These tools are based on the properties ofop-amp and that of nullor [6]. The two properties of op-amp[8] that are the key factors of our tools are, The proposed method uses the concepts based onfixators, norators and nullators.Fixators: These are theoretical two terminal deviceswith both, the current through and voltages across thecomponents are specific. Thus, fixators can be a voltagesource, a current source or a combination of both along witha series or parallel nullator. Nullators are theoretical twoterminal components with both, the current through andvoltage across them are equal to zero.Norators: They are theoretical two terminalcomponents with both, the current through and voltageacross the components are unspecific.Nullor : They are theoretical two port network with anullator at its input port and norator at its output port.Fig.1. Fixators; (a)&(b) voltage fixators ; (c)&(d) current fixators; (e)symbol of a fixator.IJERTV3IS070787Nullor represents an ideal amplifier with infinite gain[6] and its input output behavior is,IJERTSection 2 introduces the proposed tools – voltagefixator and current fixator using op-amp. Their circuitarrangements and usage are shown with some discussions.Section 3 contains a diode circuit, a BJT circuit and a simpleJFET circuit as examples. Section 4 explains how to usecurrent mirrors as current sources in our method and itsdesign. Section 5 checks the future scope of the proposedmethod and finally section 6 concludes the proposed method.Fig.2. (a) nullator; (b) norator; (c) nullor; (d) nullor model of op-amp. The input terminals of op-amp draw negligiblecurrent.The differential input voltage between its inputterminals is close to zero.The tool in Fig.3 (a) can be used to fix the voltagebetween two nodes. In addition, this tool helps us to find thevalue of bias supporting component that satisfies the targeteddesign. For example, to fix 5 V between X and Y, we haveto set Vdc 5 V, and remove the existing bias supportingcomponent, if any. Resistor R is optional and it has noparticular function at all. It is just a placeholder for one of thetwo terminals of bias supporting component. If it is using, itsvalue must be 10 MΩ to make sure that the current flowingthrough it is close to zero. As mentioned earlier in thisarticle, for every critical spec, there is a controlling voltagesource, current source or power-conducting component inthe circuit. In our method, op-amp output does exactly thesame function what a bias-supporting component do. That isin this example; op-amp output takes the value to make itsinput equal to zero. By analyzing the output, we can easilyfind the value of required bias-supporting component, that ifused in the actual circuit will satisfy the design, i.e., in ourexample fix 5 V between X and Y. Use of these tools aretemporary. They are removed when the final design isobtained and instead place the appropriate bias-supportingcomponent.www.ijert.org911
International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 7, July - 2014Fig.3. Usage of (a) Voltage fixator; (b) current fixator.R3 (1.763-0.673)/1.135 mA 960.35 Ω.IJERTIn Fig.3 (a), value of resistor R 10 MΩ, therefore inthis example, the circuit is source isolated. Thus, the solutionobtained from our method can be used for calculating thevalue of bias-supporting component for any given biassource, providing the value of that source. That is, in thisexample, if the bias source is a 12 V DC voltage source, thesolution of our method is useful even if the source voltage ischanged to a different value. In Fig.3 (b), usage of a currentfixator is shown and it fixes current between nodes X and Y.Rest of the arrangement is similar to that of Fig.3(a).original circuit (Fig.5 (a)), current entering R3 must be 1.135mA to get a diode current of 1 mA. Now place a currentfixator of 1.135 mA to the output of L.H.S network as shownin Fig.5 (c). Analyzing the circuit, current to and voltage atnode A’ are 1.135 mA and 1.763 V respectively. Now wehave enough data to calculate value of R3.Another usage of the proposed method is shown below.Fig.4. Network 1 and network 2 connected through port P1.In Fig.4, network 1 contains the bias source andnetwork 2 contains the non-linear device. Network 1provides the required biasing for the non-linear device innetwork 2. Port P1 separates the two networks. Usingfixators, we can nullify [3] port P1. Network 2 can beseparated from network 1 without altering the operatingpoint of non-linear device by adding Fx(V1, I1) to input ofnetwork 2. If we want to preserve both the networksunchanged, we should add a similar fixator to output ofnetwork 2. Using this theory, a diode circuit is solved for agiven design and is shown below.In Fig.5 (a), a diode circuit is shown with unknownresistor R3. We have to find value of R3 such that currentflowing through the diode must be 1 mA. If we remove R3,we get two sub circuits, L.H.S is a powered network andnetwork in R.H.S is an unpowered one. A powered networkshould contain one or more sources. In the next step, addcurrent fixator of 1 mA to R.H.S network (Fig.5 (b)) to biasthe diode D1 at the desired operating condition. Analyze thecircuit to find voltage at and current entering node A’. Itshould be 0.673 V and 1.135 mA. This means, in ourIJERTV3IS070787Fig.5. (a) A diode circuit; (b) Inserting current fixator to fix diode current at1 mA; (c) Finding node 2 voltage for the required design.III.IMPLEMENTATION OF THE TOOLS WITH EXAMPLESa).Consider a simple diode circuit as depicted in Fig.6(a). Here the design is to find the value of voltage source V1so that the current flowing through diode D1 is 1 mA. Nowthe design process starts by inserting current fixator to thecircuit, in such a way that the current flowing through thediode will freeze at 1 mA. The circuit arrangement is asshown in Fig.6 (b). The next step in our design procedure isto set up the circuit in a breadboard as in Fig.6 (b) andanalyze the voltage and current values at all nodes. Theresistor R in the above arrangement must be sufficiently highto get acceptable result. Results of the analysis are shown intables 1.1 and 1.2.www.ijert.org912
International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 7, July - 2014Fig.6. (a) A simple diode circuit; (b) Current fixator is added to fix currentthrough diode at 1mA.TABLE 1.1.Fig.8. (a) finding value of R2 using current fixator for a diode current of1mA. (b) Value of R2 changed to 2.28 KΩ.TABLE 2.1. ANALYSIS RESULTS OF DIODE CIRCUIT IN Fig.8(a)ANALYSIS RESULTS OF DIODE CIRCUIT IN Fig.6(b)VoltageNode 1Node 2Node 3VoltageNode 1Node 2Node 3Value (V)2.2651.0430.573TABLE 1.2. ANALYSIS RESULTS OF DIODE CIRCUIT IN Fig.6(b)Value (mA)1.220.221.00TABLE 2.2. ANALYSIS RESULTS OF DIODE CIRCUIT IN Fig.8(a)IJERTCurrentNode 1-2Node 2-0Node 3-0The analysis indicates a voltage drop of 2.265 V acrossA’B’ when 1 mA current flows through the diode. The laststep in our design process is to remove current fixator andinstead place V1 2.265 V and the final circuit is as in Fig.7.Analyzing the circuit in Fig.7 with V1 2.265 V, we canobserve that diode current is 1 mA.Fig.7. A voltage source of 2.265 V is placed as V1.b).Next, make some modifications to the arrangementin Fig.6 (a). Let V1 2.5 V and still we needs the diodecurrent fixed at 1 mA. As discussed previously in this article,for cases like this, we have to alter the value of one of theresistor but the selection of the resistor depends on the circuititself. In this case, we are altering the value of resistor R2.The selection of R2 is only one of the choices we have madein our design and selections of any other resistors are alsovalid. Proceeding with the design steps, set up the circuit asshown in Fig.8 (a) and analyze. Analysis results are shown intable 2.1 and 2.2. Thus, we can calculate the value of R2.Final circuit is shown in Fig.8 (b).IJERTV3IS070787Value (V)2.5001.0430.573CurrentNode 1-2Node2-0(i.e. IR2)Node 3-0(i.e. ID1)Value (mA)1.4570.4571.000R2 (1.043/0.457 mA) 2.28 KΩ.c). Consider the common emitter amplifier as shown inFig.9 (a). The design criteria for this amplifier requires IC 1mA, maximum output voltage swing 8 VP-P and have asupply voltage VCC 12 V. In other words the operatingpoint must be such that IC 1 mA and VCE 4 V. In thiscase, we have to fix two parameters; VCE and IC. So we haveto use two fixators in this circuit; a current fixator is used tofix IC 1 mA and a voltage fixator to keep VCE fixed at 4 V.Next step is similar to what we have done in previous cases.We have to choose two resistors such that they are thecontrollers of our targeted parameters. In this case, IC is acritical spec. We know that IC βIB, where β is the currentgain of the transistor. Resistor R1 controls IB and hence IC. Inthe case of collector to emitter voltage, collector resistor RCmust take into consideration. As discussed earlier, selectionof any other option (DC source or power-conductingcomponent) is also acceptable, but the difference is that eachcomponent responds to AC design differently. The circuitarrangement for biasing design is as in Fig.9 (b). Add resistorRE as per the required VE. Here a 1.2 KΩ resistor is added atthe place of RE which gives VE 1.2 V. Value of resistor R2is taken as 10 KΩ. Setup the circuit as shown in Fig.9 (b)and analyze the circuit. The result of analysis is shown intables 3.1 and 3.2.www.ijert.org913
International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 7, July - 2014Fig.9. (a) Common emitter amplifier; (b) Fixing IC and VCE using current fixator and voltage fixator.TABLE 3.1.ANALYSIS RESULTS OF Fig. 9(b)VoltageVC VAVEVB VA’Value (V)5.211.211.86CurrentIC IRCIEIR1Value (mA)1.0001.0080.192IJERTTABLE 3.2. ANALYSIS RESULTS OF Fig. 9(b)From the results, we can calculate values of R1 and RC,as,Fig.9.1. Complete modeling using fixators.TABLE 4.1(a). ANALYSIS RESULTS OF COMPLETE MODELINGR1 (12-1.86)/192 µA 52.8 KΩ.RC (12-5.21)/1 mA 6.79 KΩ.VoltageNow in Fig.9 (a) put RC 6.79 KΩ and R1 52.8 KΩ.Again, analyze the circuit. Results of the analysis are shownbelow in table 4.Fixators can also be used for complete modeling of nonlinear devices. As mentioned earlier, complete modeling isemployed when all the parameters of a device are seen to becritical. That means for a transistor used in Fig.9 (a), if IC,VCE, VBE and IB are critical, complete modeling can be used.The complete modeled circuit is shown in Fig.9.1.Here wefix IC at 1 mA, IB at 4 µA, VBE at 0.65 V and VCE at 4 V. Ifwe setup a circuit as shown in Fig. 9.1 and measure thevarious voltages and currents, it gives measurements asshown in tables 4.1(a) and 4.1(b).Value (V)VE1.207VB1.857VC5.207TABLE 4.1(b).CurrentANALYSIS RESULTS OF COMPLETE MODELINGValue (mA)IC1.0010IE1.0060IB0.0049IR10.1897Using the readings in tables 4.1(a) and 4.1(b), we cancalculate RC and R1 as,Rc (12-5.207)/1.001 mA 6.786 KΩ and,R1 (12-1.857)/189.7 µA 53.468 KΩTABLE 4 RESULTS OF ANALYSIS WITH CALCULATED VALUES OFRESISTORSParameterValueVE1.21 VVC5.19 VIC1.003 mAIE1.009 mAIJERTV3IS070787These are close to the values of RC and R1 obtained forcircuit in Fig.9 (b).d). Next example is a fixed biased JFET network asshown in Fig.10 (a). In this case, the only requirement of ourdesign is to get a drain current of 5 mA. Therefore, we needa current fixator and which will determine the value of drainresistor RD. We cannot choose RG because gate current ofwww.ijert.org914
International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 7, July - 2014source are node 1 ( ) and collector of Q1 (-). The currentsource in Fig.11 (a) makes use of the fact that as long as thetransistor is operating in the active region, the collectorcurrent is relatively independent of collector voltage [8].Current IRC ( IC) flowing through Q results in a particularbase emitter voltage. The base and emitter terminals of thetwo identical transistors (Q and Q1) are interconnected sothat a similar current flows through Q1 (i.e. IC1).Fig.10. (a) JFET fixed biased circuit; (b) Fixing drain current using currentfixator.FET is theoretically zero. If we need to fix more parameters,we can add a source resistor or vary DC supply voltage VDDusing fixators. Gate resistor RG 10 MΩ because IGapproximately equal to zero under DC conditions. Thecircuit arrangement for the biasing design is shown in Fig.10(b).The value of output current can be controlled usingRC. We may think how to fix output current of the currentsource at a desired value. Again, fixator comes into usage.The difference from previous case is that here we employs avoltage fixator instead of a current fixator. The process startswith inserting a resistor with proper value R’. Then usevoltage fixator to fix the voltage across resistor R’ at a valueV1 such that V1/R’ IC1, which is the required current. Forexample, the designing process for a current source for anoutput current of 1 mA is shown in Fig.11 (b). Here we useR’ as 100 Ω resistor and we need a voltage fixator to fix 100mV across R’.Setup the circuit as shown in Fig.11 (b) and analyze.Results of the analysis are shown in table 6. Based upon thisobservation, we can calculate RC as,Setup and analyze the circuit in Fig.10 (b). Analysisresults are shown in table 5.TABLE 5. ANALYSIS RESULTS OF JFET FIXED BIASED CIRCUITValueVD0.734VVG4.6µVID5mAIS5mAWe can verify the correctness of our current source byusing it in circuit shown in Fig.6 (b). The new circuitobtained will be as shown in Fig.12. Setup the circuit(Fig.12) and analyze, we get the readings as shown in tables7.1 and 7.2.IJERTParameterRC (12-0.642)/880 µA 12.9 KΩ.From table 5, we can calculate RD as,RD (10-0.734)/5 mA 1.85 KΩ.Next put RD 1.85 KΩ in Fig.10 (a) and analyze thecircuit, we can observe that ID 5 mA.IV.CURRENT SOURCESFor biasing designs using the current fixator, we needconstant current sources. Voltage sources are easily availablebut current sources are not like that. The proposed tools aredesigned to do biasing designs easily, so there is a need for acommonly available current source. Current mirror can beused as a current source [1,8] and it needs only two BJT anda resistor (for the basic current mirror circuit). The value ofcurrent can be set using this resistor. The circuit for a currentmirror arrangement is shown in Fig.11 (a).Fig.11. (a) Current mirror circuit; (b) Designing current source usingvoltage fixator.TABLE 6.In Fig.11 (a), Q and Q1 are matched transistors. Thebase terminals and emitter terminals of both are connectedtogether; it makes the same VBE. Q is operating as a diodesince its base is connected to its collector. This circuit worksas a constant current source as long as the transistor operatesin the active region [8], where the output terminals of currentIJERTV3IS070787www.ijert.orgDESIGNING CURRENT SOURCE USING VOLTAGE FIXATOR:ANALYSIS RESULParameterValueVC0.642 VIC880 µAIC11 mAIE11.006 mA915
International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 7, July - 2014Fig.12. Current mirror is used as Current Source.storage elements. The success of such tests depends on theway we use these tools and where we use them.TABLE 7.1. CURRENT MIRROR IS USED AS CURRENT SOURCE:ANALYSIS RESULTSValue (V)Node 12.268Node21.044Node30.573VI.A new method for biasing design of analog circuit withpractical components has been presented. The key elementsof the method are voltage fixator and current fixator usingop-amp. Advantage of this method is that it does not needany theoretical parts and any simulation software, but thedesigning can be done in our electronics lab with the originalcomponents, which we like to use in the circuit. This avoidsneeds for approximations and is very useful for designers.This method allows us to handle the non-linear device in aneasier way and it avoids complexities associated with thebiasing design of circuits containing non-linear devices. Inaddition, the proposed tools are able to bias the non-lineardevice individually and it provides the DC sources at thedesired locations of the circuit. The scopes of the proposedtools are unlimited.CURRENT MIRROR IS USED AS CURRENT SOURCE:ANALYSIS RESULTSCurrentValue (mA)IR11.224IR20.222IR31.002ID11.002The readings obtained using circuit in Fig.12 are verymuch close to values in tables 1.1 and 1.2. This test provesthe efficiency of current mirror in our design.V.ACKNOWLEDGMENTAuthors are thankful to Dr. Reza Hashemian, LifeSenior Member, IEEE for his valuable suggestions,comments and inspiration in this research work.DISCUSSIONSREFERENCESAt present, biasing designs depend upon someapproximations and sometimes we need to neglect certainfactors. Why we take such approximations and why weavoid those small factors. It is just to make the designprocess easier and to minimize the number of iterations. Ifwe can do those designs without taking any approximationsand without avoiding any factors, it is advantageous. This iswhy the proposed tools have relevance in the presentscenario.[1]Use of fixators for biasing design is a new concept. Thescope of fixators is tremendous. This article presents theiruse in biasing design only. Fixators can be used to solveperformance problems of amplifiers, oscillators, feedbacknetworks, gain control of amplifiers and even to work with[4]IJERTV3IS070787CONCLUSIONSIJERTTABLE 7.2.Voltagewww.ijert.org[2][3][5]Reza Hashemian, “Application of Fixators-Norator Pairs inDesigning Active Loads and Current Mirrors in AnalogIntegrated Circuits”, IEEE Transactions On Very Large ScaleIntegration (VLSI) Systems, Vol. 20, No. 12, December 2012.NN Bhargav, DC Kulshreshtha and SC Gupta, Basic ElectronicsAnd Linear Circuits, Tata McGrew-Hill Publishing CompanyLimited,42nd reprint 2006.R. Hashemian, “Local biasing and the use of nullator-noratorpairs in analog circuits designs,” VLSI Design vol. 2010, 83.htmlR. Hashemian, “Use of Local Biasing in Designing AnalogIntegrated Circuits,” presented at the IEEE Int. Conf.Electro/Inform. Technol. (EIT), Ames, Iowa, 2008.Reza Hashemian,”A linear like biasing technique for nonlineardevices”.Presented in International Conference On IntegratedCircuit Design & Technology, ICICDT 2007.916
International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 7, July - 2014[6][7]IJERT[8]C. J. Verhoeven, A. van Staveren, G. L. E. Monna, M. H. L.Kouwenhoven, and E. Yildiz, Structured Electronic Design:Negative-Feedback Amplifiers, Kluwer Academic Publishers,Dordrecht, The Netherlands, 2003.E. Tlelo-Cuautle, Advances in Analog Circuits, 1st ed. India:InTech,2011, ch. 2, 3.D.Roy Choudhury and Shail B.Jain, Linear IntegratedCircuits,3rd edition, New Age International Publishers,chapter2,3 and 4.IJERTV3IS070787www.ijert.org917
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.
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.,
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.
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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)
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
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
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