4/12/2023 0 Comments Transistor and gateIncreasingly, these fixed-function logic gates are being replaced by programmable logic devices, which allow designers to pack many mixed logic gates into a single integrated circuit. CMOS uses complementary (both n-channel and p-channel) MOSFET devices to achieve a high speed with low power dissipation.įor small-scale logic, designers now use prefabricated logic gates from families of devices such as the TTL 7400 series by Texas Instruments, the CMOS 4000 series by RCA, and their more recent descendants. To reduce power consumption still further, most contemporary chip implementations of digital systems now use CMOS logic. As integrated circuits became more complex, bipolar transistors were replaced with smaller field-effect transistors ( MOSFETs) see PMOS and NMOS. Transistor–transistor logic (TTL) then supplanted DTL. For higher speed and better density, the resistors used in RTL were replaced by diodes resulting in diode–transistor logic (DTL). RTL gates were used in early integrated circuits. Unlike simple diode logic gates (which do not have a gain element), RTL gates can be cascaded indefinitely to produce more complex logic functions. The simplest family of logic gates uses bipolar transistors, and is called resistor–transistor logic (RTL). In reversible logic, Toffoli or Fredkin gates are used.Ī functionally complete logic system may be composed of relays, valves (vacuum tubes), or transistors. Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors, which may contain more than 100 million logic gates.Ĭompound logic gates AND-OR-Invert (AOI) and OR-AND-Invert (OAI) are often employed in circuit design because their construction using MOSFETs is simpler and more efficient than the sum of the individual gates. With amplification, logic gates can be cascaded in the same way that Boolean functions can be composed, allowing the construction of a physical model of all of Boolean logic, and therefore, all of the algorithms and mathematics that can be described with Boolean logic. They can also be constructed using vacuum tubes, electromagnetic relays with relay logic, fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements. Today, most logic gates are made from MOSFETs (metal–oxide–semiconductor field-effect transistors). In the real world, the primary way of building logic gates uses diodes or transistors acting as electronic switches. MOSFETs are the most common way to make logic gates.Ī logic gate is an idealized or physical device that performs a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output.ĭepending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device (see ideal and real op-amps for comparison). CMOS diagram of a NOT gate, also known as an inverter. The AND gate with inputs A and B and output C implements the logical expression C = A ⋅ B. It can also be denoted as symbol "^" or "&". For more information see Logic gate symbols article. Additional inputs can be added as needed. There are three symbols for AND gates: the American ( ANSI or 'military') symbol and the IEC ('European' or 'rectangular') symbol, as well as the deprecated DIN symbol. The function can be extended to any number of inputs. If not all inputs to the AND gate are HIGH, LOW output results. A HIGH output (1) results only if all the inputs to the AND gate are HIGH (1). The AND gate is a basic digital logic gate that implements logical conjunction (∧) from mathematical logic – AND gate behaves according to the truth table.
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