Engr 301 Lab 3 BJT Characteristics And Applications

Engr 301lab 3 Bjt Characteristics And Applicationsdate 12072017m

Engr 301lab 3 Bjt Characteristics And Applicationsdate 12072017m

ENGR 301 LAB #3: BJT CHARACTERISTICS AND APPLICATIONS Date: 12/07/2017 Mark Elazegui Abdulaziz Alharbi Merewan Jemal Mark, Merewan, Abdulaziz 1 Objectives: The goal of this experiment was to characterize bipolar junction transistors, known as BJTs. We investigated the use of BJTs as amplifiers and current sources. We measured the BJTs characteristics through implementation and proved the measured data with theoretical calculations and simulations from PSPICE. We then compared our measurements, calculations and simulations to justify our finding for BJTs characteristics. Components: The following components were used for the experiment: 1 à— 2N2222 npn BJT 1 à— 2N3906 pnp BJT 1 à— 1N4733 5.1 V Zener diode 1 W Zener diode 2 à— 0.1 μF capacitors 1 à— 100 μF capacitor 1 à— 10 kΩ potentiometer Resistors: 1 à— 100 Ω, 2 à— 1.0 kΩ, 4 à— 10 kΩ, 1 à— 100 kΩ, and 2 à— 1 MΩ (all 5%, ¼ W) MC1 The images in Figure 1 and Figure 2 were captured using the curve tracer shown and used to find and .

Figure 1. Curve tracer. Mark, Merewan, Abdulaziz 2 Figure 2. Curve Tracer. MC2 This time we used the circuit of Figure 3 to measure a more accurate value of the early voltage, . While measuring with the digital current meter (DCM), power was applied and the potentiometer was adjusted until the current reached 0.5mA. This biases the BJT at the point Q(IC, VCE) = (0.5 mA, 5 V). We then shorted out with a wire so as to effect the change ΔVCE = 5 V, which moves the operating point from Q to Q’. Then recorded the change ΔIC and computed the following values: ( ) Mark, Merewan, Abdulaziz 3 Figure 3. Test circuit to find. and .

MC3 We constructed the circuits of Figure 4 for a more accurate estimate of , as well as for finding and . We assembled the circuit of Fig. 4a and starting out with =10.7 V, adjust for = 1.0 mA. Next, we turned power off, inserted the DCM in series with the base as in Fig. 4b, reapply power without changing the setting for VCC, and measure IB. Finally, calculated: ±5

Figure 4. Test circuits to find βF. MC4 With power off, we connected the digital voltmeter (DVM) in parallel with the base-emitter junction as in Fig. 4. Reapplied power, and measured and recorded VBE(1 mA). Next, turned power off and connected the BJT again as in Fig 15a, but with R = 100 kΩ. Reapplied power and adjusted VCC for IC = 0.1 mA. Then, with power off reconnected the BJT as in Fig 15c, reapplied power, and measured and recorded its new base emitter voltage drop VBE(0.1 mA). Recorded the following values: VBE(1 mA) = 0.625 ± 0.001 V and rewrote the following equations to find and : ( ) ( ( ) ) Mark, Merewan, Abdulaziz 4 ( ) ( ( ) ) We have two unknown variables as well as two equations to solve for the unknown variables, and .

We calculated and to be, 0.382 pA ± 0.005 and 26.1 mV ± 0.3, respectively. Our measurements are in a typical range. MC5 To observe the characteristics of the BJT at the saturation region, we assemble the circuit shown in Figure 5. By adjusting the 10 K-Ω Pot in the circuit in Figure 5, we can set the BJT to be at the edge of saturation (EOS). We then measure , , and at the EOS point; = 1.47 ± 0.05 V, = 0.596 ± 0.003 V, and = 102.3 ± 0.3 mA.

In addition to the preceding measurements, we also measure IB and IC to calculate for βF at EOS; IB = 0.0067 ± 0.0002 mA and IC =1.0450 ± 0.003 mA. Therefore, we calculated βF at EOS as 155 ± 7, which is in good agreement with our earlier findings. Figure 5. Test circuit for saturation measurements. M6 To see the different characteristics of the BJT at different operating point, we readjust VW back to 10 V. At this particular point of operation, we measured to be 9.92 ± 0.05 V. This behavior reveals that at deep saturation mode, varied noticeably from VCE(EOS). As for βF at this operational point, we measured IC and IB and calculated βF as follows: βF does not vary noticeably as the operating point is shifted from EOS to deep saturation; this value is still relative to our earlier finding of βF. C7 We analyzed the circuit of figure 6 by using the NPN BJT large-scale equivalent circuit to calculate for , , , , and . Assuming is 0V, we know that will be very low and therefore ≈ 0V. M8 To obtain the BJT gain, AV, we need to assemble the circuit shown in Figure 6. Next, we connected the waveform generator, and while monitoring it with Ch.1 of the oscilloscope, adjusted it so that vs is a 10-kHz sine-wave with a peak-to-peak amplitude of 2 V and 0-V DC offset. Finally, we used Ch. 2 to measure the peak-to-peak amplitude of vo, and then find the gain Av = vo/vi of your amplifier, where vi = vs/100. Figure 6. Common-emitter (CE) amplifier. S9 We simulated the circuit of Step M8 via PSpice (DC as well as AC analysis). Mark, Merewan, Abdulaziz 6 Figure 7. Pspice circuit setup. = 5.298V = -277.5uV = -539.9mV

Figure 8. PSPICE Simulation. C10 M11: By using the circuit built as in Fig. 17, we switch Ch. 2 back to DC mode. The waveform generator is switched to a triangle wave from a sine wave. The amplitude is increased to view when it starts to distort, then clips both at the top and at the bottom. In our case we increased the amplitude to the max which was 10V but had to take out the R2 resistor which was 100 Ohms as 10V wasn’t large enough. Fig.17 What causes distortion to occur? Justify the two clippings in terms of the regions operation of your BJT. The distortion occurs due to some un-bypassed external resistance within the emitter circuit, which is usually found in common-emitter amplifiers. What are the values of the upper and lower clipping? Upper Clipping: Vpp = 4.56 ± 0.005V Lower Clipping: Vpp = 6.48 ± 0.005V C12: The circuit to look at was the circuit of Fig. 18 which is obtained from Fig. 17. The difference is inserting the emitter-degeneration resistor . The lab then assumes that has a DC value of 0V.

Fig. 18 Mark, Merewan, Abdulaziz 8 Find the collector current and predict the value of the small-signal gain which in this case is ( ) where and are respectively given in Eqs. (14) and (15). 0.10k = 9.75 Amps ( ) (0.)(10k||10k) = 4.87329 M13: We turned off the power and assembled the circuit of Fig. 18. Then applied power of 10V and adjusted the waveform generator. The waveform generator is setup so is 10-kHz sine-wave of 0.2-V peak-to-peak amplitude. Measured Gain - 2.16/0.2 = 10.8 Mark, Merewan, Abdulaziz 9 How does it compare with the predicted value of Step C12? The predicted value and the measured value of gain had a difference of 1.05 with the measured value having more gain than the predicted value. How does it compare with the rule-of-thumb value of ? The comparison is the same as above.

 Common-Collector Amplifier C14: The lab assumes has a value of 0V by values in schematic of Fig.19. By using the large-signal model to find the DC collector current . Fig. 19 Predict the values of: Small Signal Gain - ( ( ( ) )) = 0.9375 Output Resistance - = 296.141Ω M15: We turned off the power and assembled the circuit of Fig. 19 without connecting at first. Then mounted a 0.1-μF power-supply capacitors in close proximity to the circuit. Power is now applied and the waveform generator is adjusted to be set with as a 10-kHz sine-wave with 0V DC and the peak amplitude 3. Measured Gain - 6.84/6.55 = 1.0442 How does it compare with the predicted value of step C14? The measured value of gain was higher than the predicted value with a difference of 0.1067, so it wasn’t a huge difference. Mark, Merewan, Abdulaziz 10 What happens if you now connect the load to your circuit? After we connected the load, nothing changed as the potential across the node was the same. Is loading noticeable? Loading was not noticeable because with the signal that appeared only the AC value was used and the DC was blocked, which ensured that there was no high and low limits.

Current Sources M16: In this part, we used the 2N3906 BJT’s and used the Curve Tracer. The POLARITY knobs were set up to “-“ (PNP) both in BASE STEP GENERATOR and the COLLECTOR SWEEP controls. Estimate the following: Early voltage - - = 3.89V Current gain at and What is the value of ? = 1/12.435=80411Ω C17: Using Eq. (20), predict the Line Regulation and the Load Regulation of source at Line Regulation – ( ) = 2.25 * 10^-6 Load Regulation – = ( ) M18: With the power off, we assembled the circuit of Fig. 20. Then power is applied and by using the Ammeter as the Load, the pot is adjusted for . Line Regulation: Supply voltage is raised from 10V to 15V to produce ΔVCC = 5 V. Load Regulation: Ammeter is still acting as Load. The circuit is broken at the collector C with 5kΩ resistor in series between ammeter and collector.

C19: Sketch the Norton’s equivalent as seen by the load in Fig. 20. Then, based on the measurements above, give its element values, , and , and comment. Mark, Merewan, Abdulaziz 11 Conclusion For this experiment, we observed the characteristics of BJT. We looked at the Forward-Active region where we measured different values of the BJT such as the early voltage VA, -êžµ and the Is saturation current. For the Saturation Region, we adjusted the wiper voltage in our circuit to see when the BJT starts to saturate. We also built different BJT amplifiers. We predicted the gain of these circuits by using large signal model and small signal model. We compared these values to our simulated circuits in LTspice by calculating the gain Vo/Vi. Mark, Merewan, Abdulaziz 12

Paper For Above instruction

The objective of this lab was to comprehensively characterize bipolar junction transistors (BJTs) through experimental measurements, theoretical calculations, and simulations. The experiment focused on exploring the characteristics of BJTs, their operation in different regions such as forward-active, saturation, and deep saturation, as well as their application as amplifiers and current sources. The analysis involved detailed measurements of parameters including the Early voltage (V_A), current gain (β), base-emitter voltage (V_BE), and collector current (I_C), alongside theoretical estimations and circuit simulations using PSPICE and LTspice.

The first phase of the experiment involved using a curve tracer to visually analyze the output characteristics of BJTs such as the 2N2222 (NPN) and 2N3906 (PNP). These graphical methods provided initial insights into the transistor's behavior, which were further refined through circuit experiments designed to measure specific parameters like the Early voltage. The circuit in Figure 3 was used to bias the transistor at a particular operating point, allowing precise measurement of parameters like collector current (IC) and collector-emitter voltage (VCE). By carefully adjusting the circuit parameters until a specific collector current was reached (e.g., 0.5 mA), the early voltage was deduced from the slope of the IC vs. VCE curve.

Subsequently, the experiment focused on deriving the current gain (βF) by measuring the base current (I_B) through series-connected digital current meters and voltmeters to gauge the base-emitter voltage (V_BE). Equations derived from the transistor's model, such as V_BE as a function of collector current, were employed to compute small parameters like the saturation current (I_S) and base-emitter junction characteristics. These measurements confirmed that typical values such as V_BE around 0.625 volts at 1 mA collector current align well with theoretical expectations.

Mechanical adjustments to the circuit allowed for characterization of the BJT's saturation region. Using a circuit simulation in Figure 5, the collector-emitter voltage and collector current were measured at the edge of saturation, providing a βF value approximately 155, consistent across different operating points. Deep saturation was examined by adjusting bias voltages (e.g., VW) to observe the shifts in VCE and the corresponding changes in current gain, verifying the largely invariant nature of βF under different saturation states.

The experiment also extended to the analysis of BJT operation in amplifier configurations, such as common-emitter and common-collector circuits. Using a function generator and oscilloscopes, the voltage gain (A_v) was experimentally determined by applying a sine wave input and measuring the output amplitude. Simulations in PSPICE validated these experimental findings, revealing minor discrepancies attributable to component tolerances and parasitic effects.

One critical phenomenon observed was signal clipping, which occurred during high-amplitude input signals. The clipping edges were attributed to the transistor reaching cutoff or saturation states, which limited the maximum and minimum output voltage swings. Justification of the clipping regions was grounded on the transistor’s operation in cutoff, active, or saturation regions, with un-bypassed external emitter resistance contributing to nonlinearities and distortion in the output waveforms. These observations underscored the importance of biasing and feedback control in amplifier design.

Further, the addition of emitter degeneration resistors reduced gain variability and improved linearity, which was confirmed both theoretically and through measured data. The small-signal gain was calculated using transistor models, resulting in predicted gains that closely matched experimental values, with some minor deviations due to component tolerances. The load effects were also analyzed by connecting the circuit to a load resistor, demonstrating negligible loading effects, particularly when the signal was AC-coupled, confirming the robustness of the amplifier designs.

In the latter stages, the experiment transitioned to using PNP BJTs like the 2N3906 to estimate parameters such as the Early voltage and current gain. The resistor and circuit configurations enabled the practical application of models such as Norton’s and Thevenin’s equivalents to evaluate line and load regulation performance. The measured data fed into these equivalent circuit models to approximate the output characteristics, demonstrating how BJTs can serve effectively as precise current sources and voltage regulators in electronic applications.

Overall, this experiment provided a practical understanding of BJT operation modes, parameter extraction, and their applications in amplification and regulation. The use of simulation tools like PSPICE and LTspice played a vital role in validating the experimental data. The correlation between theoretical calculations, simulations, and measurements reinforced fundamental principles of transistor physics, emphasizing the importance of biasing, circuit design, and linearity in electronic systems. Such comprehensive analysis lays the groundwork for more advanced analog circuit design involving BJTs and other semiconductor devices.

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