ce mirror lab3b
Figure 1. Common-emitter current mirror amplifier schematic

1. Lab goals

  • 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 current mirror 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 the values of your power supplies Vpp and Vnn:

  • Heads: Vpp = 10 V and Vnn = 0 V.

  • Tails: Vpp = +5 V and Vnn = -5 V.

From Common-emitter current mirror amplifier schematic, ignore (remove) L1 and find the values required of each end of part of the potentiometer Rtop and Rbottom (Rtop + Rbottom =10kΩ) so that the collector current of Q1 is about 5 mA and Vout = (Vpp + Vnn) / 2.

  • Build this circuit (still omitting 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) to your built circuit. These are placed physically close to your circuit and across 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 inductor L1.

  • Measure the resulting DC bias point. Does the collector current of Q1 stay the same? What about VOUT (DC)? What can you say about the collector current of Q3? Doe these make sense?

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

4. References