Copy of BJT XNOR Gate (Quadrature Square Wave Test Signals)

BJT implementation of XNOR logic gate. Vin1 and Vin2 are the input signals. The output is at the junction of Rc and the collectors of Q1 and Q2. I intend to have the two input signals to be equal in frequency but in quadrature for observing the behavior in Transient Analysis. However I cannot configure the phase of a clock source so I used a sine wave input and applied it to a zero crossing detector to produce the equivalent quadrature signal. 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.