C-MOS 3 inputs AND gate


Even though we've been playing with digital circuits that have just two inputs, that doesn't mean we can't have more than two inputs. Here's a C-MOS AND gate that has three inputs. Try and figure out how 3 inputs produce a 1 output from the schematic.

After you've finished the wiring, turn power ON. You know by now how AND gate works, so we won't go into detail here. But can you look at the schematic and figure out the setting for the three keys so that you get a 1 output?

Try it... and then see if you were right. Here's how this circuit works: S1 and S2 are connected to one NAND. When they are both 1, the NAND outputs a 0. This 0 then makes up the input of another NAND, causing its output to become 1. This 1 output then goes to another NAND gate (see it on the schematic?).

There it makes up one input, along with the input from S3 making up the other. When these are both 1, the NAND's output goes to 0. This output is used for both inputs of the second NAND, causing it to become 1 ... and the LED lights. Seems simple, doesn't it?

Believe it or not, even complex computers operate by using the same basic principles we're using with the digital circuits in this kit.








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