The semiconductor logic gates, on the other hand, acts as a high-gain voltage amplifier, which sinks a tiny current at its input and produces a low-impedance voltage at its output. The switch circuit creates a continuous metallic path for current to flow (in either direction) between its input and its output. Also, there is a fundamental structural difference. They are much faster, consume much less power, and are much smaller (all by a factor of a million or more in most cases). CMOS uses complementary (both n-channel and p-channel) MOSFET devices to achieve a high speed with low power dissipation.Įlectronic logic gates differ significantly from their relay-and-switch equivalents. To reduce power consumption still further, most contemporary chip implementations of digital systems now use CMOS logic. As ICs became more complex, bipolar transistors were replaced with smaller MOSFETs. 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 (DTL). RTL gates were used in early integrated circuits (ICs). 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, which is called resistor-transistor logic (RTL). 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 Boolean logic, and therefore, all of the algorithms and mathematics that can be described with Boolean logic.Ī functionally complete logic system may be composed of relays, valves (vacuum tubes), or transistors. Logic gates are primarily implemented using diodes or transistors acting as electronic switches, but can also be constructed using vacuum tubes, electromagnetic relays (relay logic), fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements. Depending 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. A Logic Gate is an idealized model of computation or physical electronic device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output.
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