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22.4: Procedure

  • Page ID
    37305
  • 22.4.1: AC Circuit Voltages

    1. Consider the circuit of Figure 22.3.1 using Vcc = 15 volts, Vee = −12 volts, Rs = 10 k\(\Omega\), Rb = 33 k\(\Omega\), Re = 22 k\(\Omega\), Rsw1 = 220 \(\Omega\), Rsw2 = 1 k\(\Omega\), Rc = 15 k\(\Omega\), Rload = 20 k\(\Omega\), Cin = Cout = 10 \(\mu\)F and Ce=470 \(\mu\)F. Using the approximation of a negligible DC base voltage, determine the DC collector current and \(r’_e\), and record these in Table 22.5.1. Using the \(r’_e\), calculate the expected \(Z_{in}\), \(Z_{in(base)}\), and \(A_v\) for the X, Y and Z connection points for Ce (shown at position X in the schematic). Record these in Table 22.5.2. If a transistor curve tracer or beta checker is not available to get an approximate value of beta for the transistor, estimate it at 150.

    2. Build the circuit of Figure 22.3.1 using Vcc = 15 volts, Vee = −12 volts, Rs = 10 k\(\Omega\), Rb = 33 k\(\Omega\), Re=22 k\(\Omega\), Rsw1 = 220 \(\Omega\), Rsw2 = 1 k\(\Omega\), Rc = 15 k\(\Omega\), Rload = 20 k\(\Omega\), Cin = Cout = 10 \(\mu\)F and Ce=470\(\mu\)F. Connect Ce to postion X. Disconnect the signal source and check the DC transistor voltages to ensure that the circuit is biased correctly (note, the DC equivalent circuit is very similar to the ones used in the Emitter Bias Exercise and should exhibit similar DC voltage readings).

    3. Using a 1 kHz sine wave setting, apply the signal source to the amplifier and adjust it to achieve a load voltage of 2 volts peak-peak.

    4. Measure the AC peak-peak voltages at the source, the base, and the load, and record these in Table 22.5.3. The load waveforms may exhibit some asymmetry due to distortion so be sure to record the peak-peak voltage not the peak. If asymmetry is observed between the positive and negative peaks, make a note of it. Also, capture images of the oscilloscope displays (\(V_s\) with \(V_b\) and \(V_b\) with \(V_{load}\)).

    5. Set the distortion analyzer to 1 kHz and % total harmonic distortion (% THD). Apply it across the load and record the resulting reading in the final column of Table 22.5.3.

    6. Remove the distortion analyzer and connect Ce to position Y instead of X. Repeat steps 3, 4 and 5.

    7. Remove the distortion analyzer and connect Ce to point Z instead of Y. Repeat steps 3, 4 and 5.

    8. Using the measured base and load voltages from Table 22.5.3, determine the experimental gain for the transistor. Using the measured source and base voltages along with the source resistance, determine the effective input impedances via Ohm’s law or the voltage divider rule. Record these values in Table 22.5.4. Also determine and record the percent deviations.

    22.4.2: Computer Simulation

    9. Build the circuit in a simulator and run three sets of simulations, one for each of the three Ce positions. For each trial, set the AC source voltage to the value measured in Table 22.5.3 (\(V_{S Exp}\)). Run a Transient Analysis and inspect the voltages at the base and load. The AC source voltage may have to be adjusted slightly to achieve the desired the desired 2 volt peak-peak load voltage. Record these values in Table 22.5.5. Add the Distortion Analyzer instrument at the load and record the resulting value.

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