Electronics 245
Practical 3 Report
Name:
SUID:
Introduction
In this practical a simple common emitter transistor amplifier is used to demonstrate the principles of
bias stability and ac output swing. Each student must work individually and must upload an individual
report onto SunLearn.
SPICE models of the components will be available on the course webpage. You must make use of the
provided models.
Follow the Instructions below and only provide what is asked for. You must make use of this template.
N.B. You can plot the waveforms directly in SPICE for this practical. Please ensure that waveforms and
axes are legible.
A BJT Amplifier with Bias Stability
The amplifier is shown in the sketch. A 2N2219 npn transistor is provided. The transistor SPICE model
is available on SunLearn.
Design the amplifier with bias stability in mind, with quiescent (𝑄) values of 𝐼𝐶𝑄 = 1 mA and 𝑉𝐶𝐸𝑄 =
5 V. Assume 𝛽 = 100 and 𝑉𝐵𝐸(𝑜𝑛) = 0.65 V.
Sketch the amplifier load line (𝑣𝐶𝐸 versus 𝑖𝐶 ) by hand. Show the Q-point of the amplifier on the load
line sketch.
How well is your amplifier designed in terms of symmetrical output swing? Give reasons for your
answer.
A sinusoidal input waveform (𝑣𝑆) with an amplitude, 𝑉𝑝𝑘 , of 100 mV and a frequency of 1 kHz is now
applied.
Do a SPICE-simulation of the circuit and plot the output and input voltage waveforms versus time on
the same graph. Assume that the resistor values you calculated are available.
Determine the voltage gain (𝐴𝑣 = ∆𝑣𝑂 /∆𝑣𝑆 ) of the amplifier from these waveforms.
Provide your SPICE code
Increase the amplitude of the input signal, 𝑉𝑝𝑘 , to 500 mV and plot the output and input
voltage waveforms versus time on the same graph.
What is now observed?
Why is this observed?