Introduction to Logic Gates
XNOR
Contents
XNOR stands for exclusive NOR and is an XOR gate with its output inverted. So, its output is at “1” when the inputs have the same value and “0” when they are different. XNOR operation is represented by the symbol (·). So Y = A (·) B. You can see XNOR logic gate symbol in Figure 20 and its truth table right below it.
Figure 20: XNOR logic gate.
| A | B | Y |
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
So its output will only be at “1” when all its inputs have the same value. Otherwise its output will be “0”.
If you need more than two inputs, you will need to add an AND gate like shown in Figure 21. Another way is to use the circuit shown in Figure 18 adding an inverter on its output.
Figure 21: Expanding XNOR inputs.
As an example of integrated circuit with XNOR gates we have 747266 and you can check its pinout in Figure 22.
Figure 22: 747266 integrated circuit provides four two-inputs XNOR gates.