"An inverter using a BJT (like an NPN transistor) is configured in a common-emitter setup. The input signal is applied to the base through a base resistor (R1), while the output is taken from the collector. A collector resistor (R2) is connected between the collector and the power supply (Vcc). When the input is low, the transistor is off, and the output is pulled high. When the input is high, the transistor turns on, and the output is pulled low. This creates an output that is the logical opposite of the input."