# How does this inverter make the AND-gate better?

I am very new to electronics and just started learning about logic gates.

I read about the AND gate and learned about its boolean algebra, but I also wanted to make one myself using MOSFETs which I learned about earlier. The AND-gate I made was pretty much identical to the one in picture 1. The only difference is that mine was implemented in an entire circuit. But I will use this picture because it's simpler and illustrates the problem more clearly.

Not sure if this was a good (or best) way to create an AND-gate using MOSFETs I started looking on the web for optimal constructions. Then I found this earlier post on engineering exchange which is very much a similar question to mine. However, it did not help me because I did not actually understand the explanations. This is because the explanation was meant for people with more advanced knowledge.

There is a picture of the AND-gate with the inverter below:

Here are my questions:

1. Could you explain to a less knowledgeable person in electronics why the AND-gate is improved by adding the inverter?

2. Is this inverter trick normally used in other types of logic-gates?

3. Is this AND-gate design using the inverter considered the "best AND-gate design" or are there multiple different designs for different use cases?

4. This is somewhat similar to question 3: Is there a generally considered best design for all the different logic gates? Is there a way to prove logic-gate design x is more efficient than all the other ones? Or does it mostly come down to price when producing them as long as it gets the job done?

• What are you referring to as the "inverter component"? There is a part of that circuit that I would call an inverter, but it's not made of "two resistors". Sep 6, 2023 at 21:01
• @Hearth, The author of the post-question I linked asked why there was "an additional inverter part" in the logic gate. I thought I was referring to the two resistors. Am I incorrect? Sep 6, 2023 at 21:05
• You've mistakenly identified what part of this is the inverter. The inverter is not the two resistors at the top; the inverter is the resistor and MOSFET on the right. "Inverter" here means the same thing as "NOT gate." As far as I know, that's an ordinary NMOS NOT gate. Sep 6, 2023 at 21:06
• Yes, and AND gate is made using a NAND gate plus a NOT gate. NOT gates are also called inverters. Sep 6, 2023 at 21:09
• The problem with your AND gate is the output voltage is lower than the input voltage. If you connected the output to another gate, the second gate's output would be even lower. After a few gates the voltage would always be 0 so the gates wouldn't work. A good gate has to make sure the output voltage is at least as good as the input voltage (closer to Vcc when high, closer to 0V when low). Sep 6, 2023 at 21:09