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A CMOS transistor NAND element. V dd denotes positive voltage.. In CMOS logic, if both of the A and B inputs are high, then both the NMOS transistors (bottom half of the diagram) will conduct, neither of the PMOS transistors (top half) will conduct, and a conductive path will be established between the output and Vss (ground), bringing the output low.
Together with the AND gate and the OR gate, any function in binary mathematics may be implemented. All other logic gates may be made from these three. [3] The terms "programmable inverter" or "controlled inverter" do not refer to this gate; instead, these terms refer to the XOR gate because it can conditionally function like a NOT gate. [1] [3]
The NAND gate has the property of functional completeness, which it shares with the NOR gate. That is, any other logic function (AND, OR, etc.) can be implemented using only NAND gates. [2] An entire processor can be created using NAND gates alone. In TTL ICs using multiple-emitter transistors, it also requires fewer transistors than a NOR gate.
A truth-functional approach to logical operators is implemented as logic gates in digital circuits. Practically all digital circuits (the major exception is DRAM) are built up from NAND, NOR, NOT, and transmission gates; see more details in Truth function in computer science.
See also: Diode logic § Active-high OR logic gate. The wired OR connection electrically performs the Boolean logic operation of an OR gate using open emitter or similar inputs (which can be identified by the ⎏ symbol in schematics) connected to a shared output with a pull-down resistor. This gate can also be easily extended with more inputs.
Diagram showing a way of making a logical inverter (NOT gate) from a NAND gate. Date: 22 December 2008: Source: Own work: Author: Inductiveload: Permission (Reusing this file) Own work, all rights released (Public domain)
The 3-input Fredkin gate is functionally complete reversible gate by itself – a sole sufficient operator. There are many other three-input universal logic gates, such as the Toffoli gate . In quantum computing , the Hadamard gate and the T gate are universal, albeit with a slightly more restrictive definition than that of functional completeness.
Schematic of basic two-input DTL NAND gate. R3, R4 and V− shift the positive output voltage of the input DL stage below the ground (to cut off the transistor at low input voltage). Diode–transistor logic (DTL) is a class of digital circuits that is the direct ancestor of transistor–transistor logic.