Logic gate input?

Question

Is a negative input or output into or out of a logic gate generally considered 0 and no input or a positive pull considered 1? Also are PNP or NPN transistors generally used to make logic gates?

Answer 1

Hi,

For a logic gate, Boolean algebra is used. Therefore, there are two levels, 0 or 1. For low level, usually lower voltage (either negative or ground) is used while for high level, higher voltage is used.

However, there is exception and it depends on the circuit design. Here shows the implementation of a NOR gate using pnp transistors. You can either define high voltage to be 1 or 0 but the circuit has to be changed accordingly.

http://www.kodkodkod.com/files/transistor_level_diagram.htm

pnp and npn are bipolar transistors. They are widely used to construct logic gates. However, nowadays, CMOS is more common due to its lower power consumption. CMOS are made of MOSFETs and their counterparts to pnp and npn are pMOS and nMOS respectively. Here describes how MOSFETs works.

http://www.kodkodkod.com/files/MOSFETs.htm

Please let us know if you have further questions:

http://www.kodkodkod.com/index_files/submitquestion.htm

Regards,

KodKodKod Learning Consulting http://www.kodkodkod.com

Answer 2

It can be different, depending on the circuit design. A logic 0 is generally no voltage input or ground level. A logic 1 is generally a positive voltage input. However, in some cases there are exceptions. A logic 0 is still generally no voltage or ground, but if the device uses a positive ground electrical system, the logic 1 may be a negative input level. The logic 1 level is almost always not ground level, be that positive or negative. I have seen cases where the logic 1 is a positive voltage and the logic 0 is a negative voltage, not using ground level at all.

Discrete transistors can be used to make logic gates, but IC's are much more commonly used.

Answer 3

current flows through a component or it does not.
these states are indicated by 1 and 0.
if there is current flowing through the circuit(irrespective of the direction) the logic is considered as 1.
if there is no current the logic is 0.
generally npn transistors are used to make logic circuits as the flow of electrons is faster than the flow of holes

Answer 4

Not more than 4 inputs per gate.

Answer 5

YES _VE INPUT OR OUT PUT IS CONSIDERED TO B 0AND + OR NO IN/OUT PUT IS 1