SINGLE STAGE BJT AMPLIFIERABSTRACTTheoryA bipolar transistor consists of a three-layer “sandwich” of doped (extrinsic) semiconductormaterials, either P-N-P in Figure (b) or N-P-N at (d).. The schematic symbols as shown inFigure (a) and (d).BJT transistor: (a) PNP schematic symbol, (b) physical layout (c) NPN symbol, (d) layout.The functional difference between a PNP transistor and an NPN transistor is the properbiasing (polarity) of the junctions when operating. For any given state of operation, thecurrent directions and voltage polarities for each kind of transistor are exactly opposite eachother.Bipolar transistors work as current-controlled current regulators. In other words, transistorsrestrict the amount of current passed according to a smaller, controlling current. The maincurrent that is controlled goes from collector to emitter, or from emitter to collector,depending on the type of transistor it is (PNP or NPN, respectively). The small current thatcontrols the main current goes from base to emitter, or from emitter to base, once againdepending on the kind of transistor it is (PNP or NPN, respectively).
The are three types of configurations: 1) Common Emitter ConfigurationHere the emitter terminal is common to both the input and output signal. The arrangement isthe same for a PNP transistor. Used in this way the transistor has the advantages of amedium input impedance, medium output impedance, high voltage gain and high currentgain. 2) Common Base ConfigurationHere the base is the common terminal. Used frequently for RF applications, this stage hasthe following properties. Low input impedance, high output impedance, unity (or less) currentgain and high voltage gain. 3) Common Collector ConfigurationThis last configuration is also more commonly known as the emitter follower. This isbecause the input signal applied at the base is follow quite closely at the emitter with avoltage gain close to unity. The properties are a high input impedance, a very low outputimpedance, a unity voltage gain and a high current gain. This circuit is also used extensivelyas a buffer converting impedances or for feeding or driving long cables or low impedanceloads.Characteristic Common Base Common Emitter Common CollectorVoltage Gain,Av High Medium UnityCurrent Gain,Ai Less than unity Medium HighPower Gain Low High MediumInput impedance,Zin Low Medium HighOutput impedance,Zout High Medium LowThe main objectives of this experiment are 1) To differentiate the BJT configuration 2) To measure the dc and ac parameters of BJT
3) To observe the differences of voltage gain by common emitter and common collector circuit 4) To observe the waveform differences between the voltage output and voltage inputList of equipment was used in this experimentEquiment Component 1) DC Power supply 1) Breadboard 2) Oscilloscope 2) Transistor:BC 109 3) Digital multimeter 3) Resistor:1kΩ,3.3kΩ,27kΩ,120kΩ 4) Function generator 4) Capacitors:10µF,47 µF,22 µF 5) Connecting wires and clippersEXPERIMENT PROCEDURE 1) The Circuit was constructed as shown in Figure 6.2. 2) The Value of VB,VC,VE,VBE and VCE was recorded and measured in Table 6.2.The Amplifier was designed to function with the following bias:VBE~0.7V and VC 0.5Vcc. 3) A 1kHz,20mVp-p signal was applied from signal generator to the amplifier and the input and output signals on the oscilloscope was observed.The input voltage,Vin was slowly increased until the output voltage achieves maximum value without distortion.The input and output waveform was drawed to identify of configuration being used,in Figure 6.4(a) and Figure 6.4(b) respectively. 4) The voltage output,Vo was measured and the voltage gain,Av was calculated by using Equation 6.1 (Equation 6.1) 5) Step 3 and 4 for the circuit shown in Figure 6.3 was repeated,The input and output waveform was drawed in Figure 6.5(a) and Figure 6.5(b) respectively.
DiscussionIn the Figure 6.2 the type of configuration was used is the common emitter configuration andin the Figure 6.3 the type of configuration was used is common collector configuration.Fromour result it clearly indicate that circuit which is use common emitter configuration amplifiedthe circuit and the circuit which is used common collector configuration does notamplified.So the experiment that was be done agreed with the theory which are voltage gainby the common emitter circuit is high and voltage gain by the common collector circuit isunity.From the result which in table 6.2.It show us that got differences in value between thetheoretical and measured.By using theoretical we was using DC Analysis to find out thevalue VB,VC,VE,VCE by assume B=380 and VBe=0.7.By using digital multimeter we wasmeasured the value VB,VC,VE,VCE,VBE by constructing same circuit in the Figure 6.2 andFigure 6.3.The value slightly differences .So we expect that some error was interrupted ourexperiment value.One of the error is the instrument error.Each component that we used gotsome resistance .So it can affect our measured value.
References 1) Charles K.Alexander & Mattgew N.O.Sadiku (2009).Fundamentals Of Electrical Circuit Fourth Edition:McGRAW HILL. 2) Norsabrina Sihab (2011), Chapter 4 : DC Analysis of BJT notes