BJT XNOR lamp

BJT implementation of XNOR logic gate. Switch input for observing the behavior in Interactive Simulation. Switches SW1 and SW2 provides the desired voltage levels to the input of the XNOR gate. The output is at the junction of Rc and the collectors of Q1 and Q2. When the input voltages are at different logic levels one of the transistors will have its base driven positive and its emitter near ground potential. This causes that transistor to turn on and pull the output to logic low. When the input voltages are at the same logic level both transistors are off (base and emitter are both driven positive or base and emitter are both near ground potential), the output is pulled-up through resistor Rc. Note: Depending on the transistor used and the level of input voltages, the transistors may need protection against reverse breakdown of the base-emitter junction.