The CMOS one is the most commonly used today. I suggest the short description of the NAND gate here The final section gives schematics of a NAND gate in different transistor technologies. It is unfortunate that the same word is used for two purposes when in this context you need both of them to describe how transistors with gate inputs can be used to make logic gates. In that case he appeared to be referring to logic gates which are made up of transistors. Most posters here have focussed on the gate terminal of the MOS transistors, but that does not appear to be the use your instructor intended. Regarding the terminology "gate", it has two uses that need to be distinguished. I suggest you take time and learn more about the Digital System Designing to understand in depth how the transistors play a major role today. It can also be described in Boolean Equations as True (Logic 1) or False (Logic 0) Logic 1 represents 5V and Logic 0 represents 0V in Digital system design. This is now acting as a switch and the main application involves building logic devices. In PMOS, if your Gate voltage is 0V, then input=output and in NMOS if your Gate voltage is 5V, then input=output. Lets call them Input, Output, Gate (These names are just to make it easy to understand in general). Regarding your gates question, A Transistor has 3 terminals. They are different components in general. In MOSFET there are two types, PMOS and NMOS. These signify the configurations in which a transistor is made using P and N type elements We also have Field effect Transistors (MOSFETs) that are voltage controlled in nature We have Bipolar Junction Transistors (BJT) that are current controlled in nature. Some commonly used choices:ĥ V TTL: Any voltage below 0.8 V is '0', any voltage above 2.4 V is '1'ģ V CMOS: Any voltage above 2.1 V is '1', any voltage below 1.5 V is '0'ĥ V ECL: Any voltage between -1.13 and -0.8 V is '1', any voltage between -1.95 and -1.48 V is '0'. You could pick whatever choice of voltages you want, although of course it will be more convenient to make a choice that someone has already designed chips to work with. The voltages involved are how you choose to represent the logic levels, not what the levels represent. Or, of course, they can be combined with other 1's and 0's to form larger numbers, distinguish between wider arrays of choices, etc. Whether to display an 'a' or a 'b' on the screen. What do Logical 0 and 1 really represent? (as voltages) This is a topic for a complete textbook chapter, not a few short paragraphs. Many circuit topologies using PNP, for example, can be adapted with minimal changes to work with PMOS. They are not the same, but there is some analogy between the behavior of PNP BJTs and p-channel MOSFETs, and between NPN BJTs and n-channel MOSFETs. PMOS and NMOS (short for p-channel and n-channel MOS) are two kinds of metal-oxide-semiconductor field effect transistors (MOSFETs). PNP and NPN are two kinds of bipolar junction transistors (BJTs). Whether to map high voltage to 1 or 0 and low voltage to the other is up to the circuit designer - and, these days, to the mob of young engineers with torches and pitchforks who will assemble if you choose anything other than high = 1 and low = 0. Typically, in modern usage, a voltage close to the positive supply is considered a 1 and a voltage close to the negative supply is considered a 0. What do Logical 0 and 1 really represent? (as voltages).Īny two distinct voltages can be labeled as being 0 and 1 (or false and true, or 'apple' and 'orange'). You should look this up - Wikipedia is a good place to start - there is a lot of information out there. (Sorry for all the abstract language - I'm trying to cover both FETs and BJTs here). Transistors work as switches because when you put a low-powered signal on their control terminal (gate for FETs, base for bipolars) the transistor will switch from off to on, and can control orders of magnitude more power at its active terminal than you put into its control terminal. "Gate" is a poor choice of wording, because the control terminal on a FET is called the "gate". How do they actually work as "gates"? how does it relate to the input given and the actual properties of these transistors? An NMOS transistor is analogous to an NPN, but they are by no means the same. PNP and NPN are types of bipolar junction transistors (often shortened to BJT). PMOS and NMOS are types of field-effect transistors (often called FETs, the most common type of which is MOSFET). Is PMOS the same as PNP? (and NMOS same as NPN)?
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