<^< Simple Transistor Amplifier | Course Index | Improved Transistor Amplifier >^>
| Objective:
| To investigate the operation of a simple transistor amplifier.
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| Underpinning knowledge:
| Semiconductors. Transistors. Current gain. Amplifiers. Waveforms.
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| Apparatus:
| TINA circuit file, or apparatus to make the following circuit.
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| TINA Circuit File:
| Click here to download circuit file
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| Initial Settings:
| Input signal = 10mV peak, sine wave at 1kHz. Supply voltage = 10V. C1 = 1mF. RB = 100kΩ. RL = 1kΩ.
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| Requires:
| Paper, Linear graph paper, pen or pencil.
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| Instructions:
(a) Use the oscilloscope to display two or three cycles of the voltage waveforms at the base and collector of the transistor. Sketch the waveforms in and include labelled axes.
(b) Measure, as accurately as you can, the peak-peak amplitude of the input (base) and output (collector) waveforms and use this to determine the voltage gain of the amplifier.
(c) Measure and record the voltage at the collector of the transistor with respect to common (0V). Note that, for optimum operation this voltage should be approximately half that of the collector supply (i.e. about 5V).
(d) Repeat steps (a) to (c) with RB = 50kΩ and RB = 200kΩ.
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Observations:
Comment on the shape of the output waveform. Is this exactly the same as the input? If not, how does it differ? What is the phase difference between the input and output waveforms? Comment on the voltage gain produced by the stage. What is the effect of increasing and decreasing the value of base bias current?
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| Further work:
Replace the transistor with one or two common types of transistor using models available within TINA (you may have to make changes to RB or reduce the input signal amplitude to cater for different values of current gain). Determine the new voltage gain.
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<^< Simple Transistor Amplifier | Course index | Improved Transistor Amplifier >^>
