# What's the opposite of a NOT gate?

1. Jun 4, 2010

### golmschenk

I essentially need the opposite of a NOT gate. I know that sounds silly, but what I'm really looking for is something that will provide the current based on the signal sent to it so that the more sensitive circuitry sending the signal doesn't have to run higher current levels. I've found I could do this using two NOT gates in a row or an AND gate and just using both the inputs on the AND gate to be the same, but I'm guessing there must be a circuit piece already built for this. One that I can provide a signal and supply voltage to and it will provide the output current. For what I'm doing the signal voltage and supply voltage need not be the same. I just need to make sure the circuitry sending the signal doesn't have to send the higher current with the signal itself. Thanks!

2. Jun 4, 2010

### jambaugh

What you are describing is called a http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/buffer.html" [Broken].

Last edited by a moderator: May 4, 2017
3. Jun 4, 2010

### CompuChip

Are you looking for a relay?

Edit: Jambaugh looks more capable at this, I'd look at his suggestion first :)

4. Jun 4, 2010

### minerva

OK, so you want a buffer.

Using two NOT gates, or an AND gate, or some other form of buffer made from whatever logic gate chips you have available should be fine.

Alternatively, maybe use an opamp voltage follower? Or investigate buying dedicated buffer chips.

5. Jun 5, 2010

### lostinxlation

A buffer is made of 2 inverters internally. If you need to drive a long distance and need 2 (or any even number) buffers, using a series of even number of inverters is a better solution.

If you don't care about the difference in rise time and fall time, you can use pretty much any combinational logic gate to make it a buffer.

Last edited: Jun 5, 2010
6. Jun 7, 2010

### golmschenk

Awesome. Thanks for the help!

7. Jun 28, 2011

### mhearne

So the natural progression is "AND, OR, NAND, NOR, NOT, BUFFER"? Sorry, but that just doesn't sound right to me (linguistically). Let me do some research.

8. Jun 28, 2011

### KingNothing

Also called a follower.

9. Jun 28, 2011

### Jiggy-Ninja

What "progression"?

Buffers aren't really considered a logic function, since they don't really do anything to the signal, logically speaking. They just help it drive higher loads.