Help please. I built my NOR gate schematic

[fckiri]

Hey guys? I am building a simple 2 input NOR gate schematic but the wave form that it outputs is completely wrong. I attached 2 screen shots. On the plot one, the top one is the output and the two others are inputs.
Any help will be apreciated

 

[TBennettcc]

I'm afraid I don't understand why you used four devices instead of two...

See these links:

http://en.wikipedia.org/wiki/NOR_gate#Implementations

http://en.wikipedia.org/wiki/NMOS_logic

And it would help to specify whether what devices you're using (MOSFETs? BJT?) and label the part numbers and the types of components in your first picture there.

 

[fckiri]

I am using MOSFET. I am building a NOR gate from scratch, i.e starting from 2 pmos in series and 2 nmos in parallel.

 

[TBennettcc]

Your circuit does not look like either of the examples I linked to. Why don't you try building one of those, and see what happens?

http://en.wikipedia.org/wiki/File:NMOS_NOR.png

 

[jackorocko]

Your circuit does not look like either of the examples I linked to

You must have missed this enormous picture? http://en.wikipedia.org/wiki/File:Cmosunbuff.png

I would say you where on the right track fckiri

 

[TBennettcc]

Perhaps I don't understand, then...

The OP said he was using MOSFETs. The pictures I linked to with two MOSFET gates are NOR gates using "NMOS logic circuitry". The picture jackorocko linked to has a caption describing it as using CMOS logic. I figured the OP should try using the diagrams I linked to using only two gates instead of four. If he doesn't want to, that's fine.

The picture jackorocko linked to has the p-channel MOSFETs on the top in series, and the n-channel MOSFETs on the bottom in parallel, at least according to this diagram here:

http://en.wikipedia.org/wiki/MOSFET#Circuit_symbols

The symbols you have used in your simulation are backwards from what you describe you did. I am new to transistors, so I can't tell you why an NPN BJT has the arrow pointing out, but the n-channel MOSFET has the arrow pointing in. But from the diagram, it looks like that's the way the cookie crumbles.

 

[(*steve*)]

I am new to transistors, so I can't tell you why an NPN BJT has the arrow pointing out, but the n-channel MOSFET has the arrow pointing in.

The way I remember it is that the arrow points to N (same as a map).

So the arrow points in (to the N channel) of an N channel mosfet (or away from the channel if its a P channel device).

For BJT transistors the arrow points out for NPN because it's pointing to one of the N's, and in for PNP because the N is in the middle.

Sort of visual, sort of mnemonic, and also tells you something about the construction of the device.

 

[jackorocko]

http://en.wikibooks.org/wiki/Electronics/CMOS

CMOS has an advantage over a typical NMOS type gate. I guess the real question is why he chose to design that NOR gate with complimentary mosfets and why he decided to ask here how it looked. He does have the transistors switched around though That would switch the wave form that he says is wrong.