EEE2146 Microelectronics Circuit Analysis and DesignExperiment MIC2
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MIC2: Investigation of Amplifier Parameters of a Common-Collector Amplifier
Total Percentage: 5% (From 40% Coursework Mark)
1.Objective
a)To investigate the voltage gains, current gains, input impedance and output impedances with respect to different operating conditions (biasing, load and frequency) of a common-emitter amplifier.
b)To determine the transistor parameters β, rπ and rovalues at different biasing conditions.
2. Lists of Equipments and Components
Equipments / Qty. / Components / Qty.Adjustable DC power supply / 1 / BJT 2N2222A / 1
Function generator / 1 / Capacitor 10 µF (16 V) / 2
Digital multimeter / 1 / Resistors (0.25 W) / Ω: 10, 100, 4.7k, 10k, 6.2k, 100k / Each one
Dual-channel oscilloscope / 1
Breadboard / 1 / Resistors (0.25 W) /Ω: 510, 1k, 5.1k / 2
3. Introduction
Figure 1 and Figure 2 shows a common-collector amplifier circuit and its small-signal equivalent circuit. Because of the capacitors in the amplifier circuit, the voltage gain, current gain, input impedance and output impedance are functions of frequency, therefore, they are vectors or complex numbers. The valuesof , , and and their magnitudes can be determined in experiment with the below equations.
The equation for is derived according to Figure 3. is unloaded voltage gain (RL = ∞), is equal to unloaded output voltage . , where is the complex conjugate of .
At mid-band frequencies, where the effect of the capacitors, i.e. reactance, is negligible, , , and are almost independent of frequency, i.e. they are close to real numbers, Av, Ai, Riand Ro. The equations to find the values of Av, Ai, Riand Roare given below, where all the currents and voltages are almost independent of frequency.
For further information, you can refer to lecture notes or any microelectronics books.
Figure 1:A common-collectoramplifier. The voltages, currents and impedances (except VCC) have magnitude and phase. It is the same for those in Figure 2 and Figure 3.
Figure 2: Small-signal equivalent circuit of the CC amplifier
Figure 3: Circuit illustration for measuring output resistance/impedance, RO/ZO
In Figure 3 above, Zo is the internal output impedance of the network to be measured. The term network is a general term, as the circuit could be anything, an amplifier, filter, oscillator, etc. The network is drawn as a Thevenin source.
To find the output impedance the output voltage is measured first with no load resistor, then with a fixed load (purely resistive).
First, the load resistor RL is removed and output voltage (V) measured and recorded. Then RL is placed back in circuit and the output voltage under load (VL). The output impedance, Zo is now found by Ohm's Law for AC circuits.
As the load is purely resistive Z=V/I, where "V" is voltage drop across the output impedance: ( V - VL ), and "I" the output current, VL/RL. Thus:
Zo = / ( V-VL)VL/RL
or re-arranging:
Zo = / RL ( V-VL)VL
BJT pin layout:
General Guidelines:
-Plan to carry out your experiments systematically and efficiently (e.g. table for recording data, measuring points, load connections).
-Use tables to record data & calculated values.
-Use graphs to analyze recorded data and calculated values in Section 6.
-Tables and graphs are useful tools to observe the changes of variables or parameters and to compare the same variable or parameter at different operating conditions.
-Graph is more suitable than table when the total number of values involved is large. You may use MS Excel or equivalent to plot graphs.
4. Preparation before the Lab
Please refer to Appendix 1.
5. Experiments
Please record the information in a table form.
(a)Construct the circuit as shown in Figure 1, where VCC = 12 V, R1 = 4.7 kΩ, R2 = 6.2 kΩ, RE = 510 Ω, RS = 5.1 kΩ, RL = 10 Ω, C1 = C2= 10 µF. Record voltages VCC, VB and VE.From the values you have recorded here, determine the operating region for this transistor to ensure your circuit construction is correct.
(b)With 0.2 V peak-to-peak (p-p) sine-wave for vs, record p-p voltages vi, vb, ve, vc and vo at several frequencies. You have to determine the frequency values to record. Keep in mind that you are going to use the information you record here for the analysis part in 6(b). Take at least 10 data points. Use CH1 to measure vi, vbve and CH2 to measure vcvo.
(c)With f = 10 kHz (vs = 0.2 V p-p), record p-p voltages viand vo for RL = 100Ω, 510Ω, 1 kΩ, 5.1 kΩ, 10 kΩ, 100 kΩ and ∞ (no load).
(d)Change RE to 1kΩ. Record voltages VCC, VBand VE.
(e)From Part (d), with f = 10 kHz (vs = 0.2 V p-p), record p-p voltages vi, ve and vo for RL = 1 kΩ and ∞ (no load).
6. Analysis
Calculate the items below:
(a)DC current, IC and IB, the DC current gain, β (hFE) and base-emitter resistance, rπ values from Part 5(a).
(b)Overall voltage gain,, voltage gain,, current gain, and input resistance, values for each recorded frequencyfrom Part 5(b). Put the calculated values in a table form and then, plot them in a graph. (x-axis : frequency)
(c)Overall voltage gain,, voltage gain, and current gain, values for each RLfrom Part 5(c). Put the calculated values in a table form and then, plot them in a graph. (x-axis: RL)
(d)DC current, IC and IB, the DC current gain, β (hFE) and base-emitter resistance, rπ values from Part 5(d).
(e)Overall voltage gain,, voltage gain, and current gain, values for each RLfrom Part 4(e). Put the calculated values in a table form .
(f)The output resistance, Ro value from Part 4(c). Use RL= 1kΩ.
(g)The output resistance, Ro value from Part 4(e).
Note: There are many calculations in Section 6, hence you need to show deriving equation work and describing calculation work (each repeated calculation work is not required to be shown).
7.Discussions
Discuss on the below:
(a)The calculated results in Part 5(b).What is the trend on , , , and as frequency changes?
(b)The calculated results in Part 5(c).What is the trend on , , andwhen RL changes?
(c)The calculated results in Part 5(c) and Part 5(e) by comparison.What can you see to, and when REis doubled in Part 5(e) (i.e. at 10kHzcompare at the same RL)?
(d)Is there any change to the Ro from Part 5(f) to Part 5(h)? Why?
Note: When you do the discussion, try to compare the measured results with the theoretical explanation. If it is differ, justify your results.
8. Conclusions
Please re-visit the objectives of this experiment and please make necessary conclusions.
9.Report
Write a lab report consisting of experimental results, analysis, discussions and conclusions. The report should be done individually. The experimental results may be the same among the members in the group but the analysis, discussions and conclusions should be unique.
Warning:Plagiarism (copying) will be deducted 1% from the total marks for ALLSTUDENTS’sreports that are EXACTLY THE SAME. LATE submission will be deducted another 1% from the total marks.
10.Evaluation (Based on Rubrics as attached)
References: Lecture notes or any microelectronics books
~ End of Lab sheets ~~
Updated by: Zubaida Yusoff, December 2017
Appendix 1: Preparation before the lab
Name and Student ID: ______
- What is the amplifier configuration that we like to investigate in this MIC1 experiment?
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- What are the objectives of this experiment?
- ______
- ______
- Ideally, what is the voltage gain for this type of amplifier configuration?
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- Why do we use this type of amplifier configuration as a voltage buffer?
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Please bring this Appendix 1 during the lab session and submit to the lecturer-in-charge.
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