Lapenko 20

This circuit is a two-input XNOR gate built from inverters, AND and OR gates. The inverters produce the complements of the input signals A and B. The upper AND gate performs the AND logic function of the input signals A and B. The lower AND gate performs the AND logic function of the complements of the input signals A and B. The output of the two AND gates are ORed together to produce the final output. The 1 MΩ load resistor is not part of the AND circuit, its purpose is to provide a wiring point to the output of the OR gate so that the state of the output can be probed.