ce amplifier lab3a
Figure 1. Common-emitter amplifier schematic

1. Lab goals

Topics
  • Transistor (DC) bias condition solution.

  • Experience using PNP transistors.

  • Amplifier AC gain prediction, measurement, and calculation.

Your task is to match amplifier gain of Common-emitter amplifier schematic obtained from:

  • Measurements of a prototype build of the circuit.

  • Predictions of amplifier gain using the Bipolar transistor amplifier types table.

  • Calculations from the small-signal circuit analysis of the circuit.

2. DC bias solution and setup

Find a coin or some other binary random number generator. Flip the coin to set your values of power supplies Vpp and Vnn:

  • Heads: Vpp = 10 V and Vnn = 0 V.

  • Tails: Vpp = +5 V and Vnn = -5 V.

From Common-emitter amplifier schematic, ignore (remove) both Ce and L1 and find the values required of each end of part of the potentiometer Rtop and Rbottom (Rtop + Rbottom =10kΩ) so that Vout = (Vpp + Vnn) / 2.

  • Build this circuit (still omitting Ce and L1). Adjust the potentiometer to yield the proper output voltage.

  • Measure the resulting potentiometer resistances.

  • Compute the minimum value of C1 required so that the input high-pass RC filter’s -3 dB frequency is less than 100 Hz. Select a greater value than this for C1.

Add one or two power supply bypass capacitors (about 10 μF). These are placed physically close to your circuit and between the power supply nodes. Use one if using a single +10 V supply. If using dual ±5 V supplies, place one capacitor between +5 V and the reference node and a second between the reference node and -5 V.

3. AC measurements

  • Measure the signal gain vout / vin at frequencies of 100 Hz, 1 kHz, and 10 kHz.

Add capacitor Ce to the circuit and verify that the DC bias point remains the same.

  • Again, measure the signal gain vout / vin at frequencies of 100 Hz, 1 kHz, and 10 kHz.

Add inductor L1.

  • Measure the resulting DC bias point. Does the collector current stay the same? What about VOUT (DC)? Does this make sense?

  • Finally, measure the signal gain vout / vin at frequencies of 100 Hz, 1 kHz, 10 kHz, and also 100 kHz.

4. References