- Logic Gates Definition: Logic gates are defined as basic components in digital circuits that perform logical operations based on input signals.
- OR Gate Applications: OR gates detect the occurrence of one or more events, making them useful in safety systems to trigger actions when parameters exceed safe limits.
- AND Gate Functions: AND gates can act as Enable gates to allow data passage or Inhibit gates to block data, useful in frequency measurement.
- Parity Generation: Ex-OR and Ex-NOR gates are used in parity generation and checking, crucial for error detection in data.
- Inverter Uses: NOT gates, or inverters, are used to create square wave oscillators for generating clock signals due to their low power consumption and easy interfacing.
A logic gate is a digital circuit whose output follows a Boolean function of its inputs. Earlier pages covered the internals of digital logic gates. This page covers common applications of logic gates that follow from that truth table. OR combines trips. AND acts as an enable or inhibit. XOR and XNOR handle parity. NOT appears in a ring oscillator.
Application of OR gate
An OR gate goes high when any input is high. That makes it a simple way to combine independent trip sources. In a plant, one OR can start a protective action if temperature is too high or if pressure is too high.
If temperature or pressure leaves its safe band, the OR gate can drive a trip command. The following diagram shows this setup.
The figure is a typical schematic: two trip inputs feed an OR, and the OR output is the command that starts the required action.
Application of AND Gate
An AND gate can act as an enable or as an Inhibit gate. With enable high, data can pass. With inhibit asserted, the path is blocked. In a frequency counter, a known-width gating pulse lets the unknown waveform through only while that window is open. The diagram below shows this arrangement.
Application of Ex-OR/Ex-NOR Gate
XOR and XNOR gates generate and check a parity bit. The diagrams below show even and odd parity generators for four data bits.
The same gates also check a received parity bit. The diagrams below show even and odd parity check.
Figure (a) checks with XOR gates. Figure (b) checks with XNOR gates.
Application of NOT gate or Inverters
NOT gates invert a logic level. A ring of CMOS inverters can form a simple square-wave oscillators whose period tracks gate delay. Use it as a teaching and on-chip delay-cell circuit, not the usual production clock source, which is still a crystal or other precision reference. CMOS does keep static power low and the levels are easy to interface to other CMOS logic.
The figure is a ring of inverters used as a square-wave oscillator. The frequency of this generator is given by
Here n is the number of inverters and tp is the propagation delay per gate.
