The physical representation of logic gates

[seriously disabled]

What is the physical representation of logic gates on the electronic circuit? Are they simply abstract or do they have a physical existence on the electronic circuit?

[YT2095]

do you mean in terms of chips, like the 74 (TTL) or 4000 (CMOS) series for instance?

[seriously disabled]

do you mean in terms of chips, like the 74 (TTL) or 4000 (CMOS) series for instance?

 

Yes. What i meant is how they manifest themselves in the physical world and not just abstractly.

[YT2095]

well, each chip has a number, and that number tells you what is inside it.

a 7400 will have 4 NAND gates on it for instance:

 

this will give you a visual idea of what I mean: http://en.wikipedia.org/wiki/7400_series

[seriously disabled]

well, each chip has a number, and that number tells you what is inside it.

a 7400 will have 4 NAND gates on it for instance:

 

this will give you a visual idea of what I mean: http://en.wikipedia.org/wiki/7400_series

 

That's not completely what I meant.

 

Logic gates are abstract right? So I wondered what their physical or material counterpart is. In what electronic components do they manifest themselves on the electronic circuit? How does the electronic circuit know whether it's a NOT gate, OR gate or AND gate for example? What is their physical or material manifestation on the circuit?

[YT2095]

it`s the doping pattern on a silicon substrate that determines it`s function.

[jian]

The logic gates are not that abstract that they consist of electronic elements. The most basic ones are made of diodes. Unlike resistors, diodes only allow the current go through the positive direction provied that the voltage across it is not high eough to damage them. Because of this property, they are used to control the current in a circuit. Logic values are assigned on the output depends whether there is current or not. When we are not concern about the circuit, we can simply call them logic gates. They give us cirtain output when the input is injected. They are the ancestor of the computer chips.

[seriously disabled]

So if I understood correctly computers can only work with numbers of 1 and 0. Still what I don't get is how does the transistor know that say 5V is 1 and 0V is 0 without you telling him what voltage represents 1 and what 0?

Edited January 18, 2009 by Uri

[insane_alien]

its easy, a voltage is one and no voltage is zero.

 

the basic unit of a computer is the transistor, if you apply a sufficiently high voltage(to use your numbers 5V) then it will allow current/voltage to pass through it causing another one down the line. and so on like that.

[bascule]

You might want to read about transistor-transistor logic

[Alasian]

It is set up so when it is above 5V it is a 1. If it is below for example 1.5V it is a 0. In between 1.5V and 5V it is an invalid state. This is how CMOS work and a chip which holds some gates is feeding the input of the gates whatever the CMOS translates to it, either 1 or 0.