# bjt (frequency response)

```UNIVERSITI MALAYSIA PERLIS
ANALOG ELECTRONIC CIRCUITS I
EKT 104
LABORATORY EXPERIMENT 2
BJT COMMON EMITTER AMPLIFIER
(VOLTAGE GAIN VS FREQUENCY RESPONSE)
BJT COMMON EMITTER AMPLIFIER
(VOLTAGE GAIN VS FREQUENCY RESPONSE)
Introduction
Frequency domain analysis is best considered graphically via the use of frequency response
plots. The expressions used to describe frequency response are complex numbers.
G(jω ) = Re (G(jω )) + j Im (G(jω )), ω= 0,….,∞
Thus for any system G(s), frequency responses can be generated by plotting on an
argand diagram. AR = Amplitude Ratio G(jω) and φ = Phase-shift ∠G(jω )
Frequency responses show how the amplitude ratio and phase-shift change with different
frequencies. Thus frequency responses plots are plots of amplitude ratios and phase-shifts
as a function of frequency. Frequency responses are commonly plotted using either:
(a)
Polar/Nyquist plots, or
(b)
Bode diagrams
Plotting the values of the pair (AR, φ ) over some frequency range ω will give Polar Plot
of the frequency response. Nyquist Plots are also polar plots of frequency responses. The
difference between Nyquist plots and the Polar plot is that the Nyquist plots include a plot
of AR and φ as a function of -ω. However, it is usually sufficient to plot the simpler polar
representation.
Bode diagrams are frequency responses of systems where the amplitude ratio and phase-shift
properties are presented as distinct plots. That is, Bode diagrams comprise a set of 2 plots:
(a)
Amplitude Ratio versus frequency
(b)
Phase-shift versus frequency
They can then be plotted on the same graph.
1.0
The objective of this laboratory experiment is to construct a common emitter
amplifier circuit and
1.1
1.2
1.3
To measure the amplifier voltage gain low frequency response, and compare
the practical performance with the theoretical low frequency Bode plots.
To observe and record the effect of low frequency on the amplifier output
voltage – input voltage phase shift response.
To observe and record any high frequency effects on the amplifier voltage
gain and phase shift.
2.0
3.0
Measure, record all the results and discuss on the following:
2.1
What is the effect of the input coupling capacitor and bypass capacitor, on
the voltage gain frequency response?
2.2
Does the signal generator source affect the frequency response? Explain why.
2.3
How is the high frequency gain of an amplifier limited?
2.4
What can you observed at high frequencies?
Make your overall conclusion by referring to the objective of this experiment. Please
conclude in simple notes the finding from your total experiments results. (5M)
Remember that the lab report is due 1 week from today.
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