A quad gate is an IC (integrated circuit or chip) containing four logic gates. The gates can be of any type: AND, OR, XOR, NOT, NAND, NOR, and XNOR. Within any given quad gate, all four of the individual gates are normally of the same type.
A logic gate is an elementary building block of a digital circuit. Most logic gates have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltages. Quad gates can be used in various applications including:
- Flip flops
- Digital switches
- Complex Boolean functions
- Voltage-controlled oscillators
- Waveform generators
The quad NAND gate is of particular interest, because any of the basic logic functions can be derived by connecting multiple NAND gates together. This feature makes the quad NAND gate useful as a "universal digital substitute," and also can help students learn how digital logic circuits work. A CMOS (complementary metal-oxide semiconductor) chip called the 4011 quad NAND gate is one of the most widely used digital ICs in the world.