To calculate the small-signal output conductance of a common-collector (CC) bipolar junction transistor (BJT) amplifier, also known as the emitter follower configuration, you can follow these steps:
Draw the small-signal equivalent circuit:
Replace the BJT with its small-signal model, which includes the transconductance (gm), output conductance (g0), and input capacitance (Cπ). The small-signal output conductance (g0) is the parameter we are interested in calculating.
Identify the small-signal output current (Iout):
In the common-collector configuration, the output current is primarily the collector current (Ic) of the BJT. So, Iout ≈ Ic.
Apply voltage excitation at the output:
Apply a small-signal voltage (Vout) at the output terminal while keeping the input terminal grounded (or at a small-signal AC ground). This small-signal voltage will cause a small-signal output current (Iout') to flow through the load.
Find the change in output current:
Calculate the change in output current (ΔIout) due to the small-signal voltage Vout.
Calculate the output conductance:
The output conductance (g0) is the ratio of the change in output current to the small-signal voltage applied at the output terminal:
g0 = ΔIout / Vout
It's important to note that in practical amplifier circuits, the output conductance (g0) can also be influenced by other parasitic elements, such as capacitances and resistances in the circuit, which can affect its overall behavior.
To get more specific calculations for a particular common-collector BJT amplifier circuit, you would need to know the circuit values, BJT parameters, and any additional parasitic elements present in the circuit. Then, you can use small-signal analysis techniques like Kirchhoff's current law (KCL) and Ohm's law to find the small-signal output conductance.